fix #31 type records for simple types and extern keyword for methods/functions

+collection functions (map, forEach, toList, toSet, isEmpty, etc,)

.gitignore

@@ -13,3 +13,4 @@ xcuserdata
 *.gpg
 .gigaide
 /kotlin-js-store/yarn.lock
+/test.lyng

README.md

@@ -9,6 +9,10 @@ class Point(x,y) {
    fun dist() { sqrt(x*x + y*y) } 
 }
 Point(3,4).dist() //< 5
+
+fun swapEnds(first, args..., last, f) {
+    f( last, ...args, first)
+} 
 ```
 
 - extremely simple Kotlin integration on any platform
@@ -31,16 +35,42 @@ and it is multithreaded on platforms supporting it (automatically, no code chang
 
 ## Integration in Kotlin multiplatform
 
-### Add library
+### Add dependency to your project
 
-TBD
+```kotlin
+// update to current please:
+val lyngVersion = "0.6.1-SNAPSHOT"
+
+repositories {
+    // ...
+    maven("https://gitea.sergeych.net/api/packages/SergeychWorks/maven")
+}
+```
+
+And add dependency to the proper place in your project, it could look like:
+
+```kotlin
+comminMain by getting {
+    dependencies {
+        // ...
+        implementation("net.sergeych:lynglib:$lyngVersion")
+    }
+}
+```
+
+Now you can import lyng and use it:
 
 ### Execute script:
 
 ```kotlin
-assertEquals("hello, world", eval(""" 
-    "hello, " + "world" 
-    """).toString())
+import net.sergeyh.lyng.*
+
+// we need a coroutine to start, as Lyng
+// is a coroutine based language, async topdown
+runBlocking {
+    assert(5 == eval(""" 3*3 - 4 """).toInt())
+    eval(""" println("Hello, Lyng!") """)
+}
 ```
 
 ### Exchanging information
@@ -49,6 +79,8 @@ Script is executed over some `Context`. Create instance of the context,
 add your specific vars and functions to it, an call over it:
 
 ```kotlin
+import new.sergeych.lyng.* 
+
 // simple function
 val context = Context().apply {
     addFn("addArgs") {
@@ -83,22 +115,51 @@ Designed to add scripting to kotlin multiplatform application in easy and effici
 
 # Language 
 
-- dynamic 
-- async
-- multithreaded (coroutines could be dispatched using threads on appropriate platforms, automatically)
+- Javascript, WasmJS, native, JVM, android - batteries included.
+- dynamic types in most elegant and concise way
+- async, 100% coroutines, supports multiple cores where platofrm supports thread
+- good for functional an object-oriented style
 
-## By-stage
+# Language Roadmap
 
-Here are plans to develop it:
+## v1.0.0
 
-### First stage
+Planned autumn 2025. Complete dynamic language with sufficient standard library:
 
-Interpreted, precompiled into threaded code, actually. Dynamic types.
+Ready features:
 
-### Second stage
+- [x] Language platform and independent command-line launcher
+- [x] Integral types and user classes, variables and constants, functions
+- [x] lambdas and closures, coroutines for all callables
+- [x] while-else, do-while-else, for-else loops with break-continue returning values and labels support
+- [x] ranges, lists, strings, interfaces: Iterable, Iterator, Collection, Array
+- [x] when(value), if-then-else
+- [x] exception handling: throw, try-catch-finally, exception classes.
+- [x] multiplatform maven publication
+- [x] documentation for the current state
 
-Will add:
+Under way: 
 
-- optimizations
-- p-code serialization
-- static typing
+- [ ] maps, sets and sequences (flows?)
+- [ ] regular exceptions
+- [ ] modules
+- [ ] string interpolation and more string tools
+- [ ] multiple inheritance for user classes
+- [ ] launch, deferred, coroutineScope, mutex, etc.
+- [ ] site with integrated interpreter to give a try
+- [ ] kotlin part public API good docs, integration focused
+- [ ] better stack reporting
+
+## v1.1+
+
+Planned features.
+
+- [ ] type specifications
+- [ ] source docs and maybe lyng.md to a standard
+- [ ] moacro-style kotlin integration or something else to simplify it
+
+Further
+
+- [ ] client with GUI support based on compose multiplatform somehow
+- [ ] notebook - style workbooks with graphs, formulaes, etc.
+- [ ] language server or compose-based lyng-aware editor

bin/lyng_test

@@ -0,0 +1,3 @@
+#!/usr/bin/env lyng
+
+println("Hello from lyng!")

docs/Collection.md

@@ -0,0 +1,13 @@
+# Collection
+
+Is a [Iterable] with known `size`, a finite [Iterable]:
+
+    class Collection : Iterable {
+        val size
+    }
+
+See [List], [Set] and [Iterable]
+
+[Iterable]: Iterable.md
+[List]: List.md
+[Set]: Set.md

docs/Iterable.md

@@ -1,13 +1,17 @@
 # Iterable interface
 
-The inteface which requires iterator to be implemented:
+Iterable is a class that provides function that creates _the iterator_:
 
-    fun iterator(): Iterator
+    class Iterable {
+        abstract fun iterator()
+    }
+
+Note that each call of `iterator()` must provide an independent iterator.
 
 Iterator itself is a simple interface that should provide only to method:
 
-    interface Iterable {
-        fun hasNext(): Bool
+    class Iterator {
+        abstract fun hasNext(): Bool
         fun next(): Obj
     }
 
@@ -15,19 +19,26 @@ Just remember at this stage typed declarations are not yet supported.
 
 Having `Iterable` in base classes allows to use it in for loop. Also, each `Iterable` has some utility functions available:
 
+## Instance methods
+
+    fun Iterable.toList(): List
+    fun Iterable.toSet(): Set
+    fun Iterable.indexOf(element): Int
+    fun Iterable.contains(element): Bool
+    fun Iterable.isEmpty(element): Bool
+    fun Iterable.forEach(block: (Any?)->Void ): Void
+    fun Iterable.map(block: (Any?)->Void ): List
+    
+
 ## Abstract methods
 
     fun iterator(): Iterator
 
-## Instance methods
-
-### toList()
-
 Creates a list by iterating to the end. So, the Iterator should be finite to be used with it.
 
 ## Included in interfaces:
 
-- Collection, Array, [List]
+- [Collection], Array, [List]
 
 ## Implemented in classes:
 

docs/List.md

@@ -20,11 +20,11 @@ indexing is zero-based, as in C/C++/Java/Kotlin, etc.
     list[1]
     >>> 20
 
-Using negative indexes has a special meaning: _offset from the end of the list_:
+There is a shortcut for the last:
 
     val list = [10, 20, 30]
-    list[-1]
-    >>> 30
+    [list.last, list.lastIndex]
+    >>> [30, 2]
 
 __Important__ negative indexes works wherever indexes are used, e.g. in insertion and removal methods too.
 
@@ -38,7 +38,8 @@ You can concatenate lists or iterable objects:
 
 ## Appending
 
-To append to lists, use `+=` with elements, lists and any [Iterable] instances, but beware it will concatenate [Iterable] objects instead of appending them. To append [Iterable] instance itself, use `list.add`:
+To append to lists, use `+=` with elements, lists and any [Iterable] instances, but beware it will
+concatenate [Iterable] objects instead of appending them. To append [Iterable] instance itself, use `list.add`:
 
     var list = [1, 2]
     val other = [3, 4]
@@ -57,7 +58,28 @@ To append to lists, use `+=` with elements, lists and any [Iterable] instances,
 
     >>> void
 
+## Removing elements
 
+List is mutable, so it is possible to remove its contents. To remove a single element
+by index use:
+
+    assertEquals( [1,2,3].removeAt(1), [1,3] )
+    assertEquals( [1,2,3].removeAt(0), [2,3] )
+    assertEquals( [1,2,3].removeLast(), [1,2] )
+    >>> void
+
+There is a way to remove a range (see [Range] for more on ranges):
+
+    assertEquals( [1, 4], [1,2,3,4].removeRange(1..2))
+    assertEquals( [1, 4], [1,2,3,4].removeRange(1..<3))
+    >>> void
+
+Open end ranges remove head and tail elements:
+
+    assertEquals( [3, 4, 5], [1,2,3,4,5].removeRange(..1))
+    assertEquals( [3, 4, 5], [1,2,3,4,5].removeRange(..<2))
+    assertEquals( [1, 2], [1,2,3,4,5].removeRange( (2..) ))
+    >>> void
 
 ## Comparisons
 
@@ -72,19 +94,44 @@ To append to lists, use `+=` with elements, lists and any [Iterable] instances,
 
 ## Members
 
-| name                              | meaning                             | type     |
-|-----------------------------------|-------------------------------------|----------|
-| `size`                            | current size                        | Int      |
-| `add(elements...)`                | add one or more elements to the end | Any      |
-| `addAt(index,elements...)`        | insert elements at position         | Int, Any |
-| `removeAt(index)`                 | remove element at position          | Int      |
-| `removeRangeInclusive(start,end)` | remove range, inclusive (1)         | Int, Int |
-|                                   |                                     |          |
+| name                          | meaning                               | type        |
+|-------------------------------|---------------------------------------|-------------|
+| `size`                        | current size                          | Int         |
+| `add(elements...)`            | add one or more elements to the end   | Any         |
+| `insertAt(index,elements...)` | insert elements at position           | Int, Any    |
+| `removeAt(index)`             | remove element at position            | Int         |
+| `remove(from,toNonInclusive)` | remove range from (incl) to (nonincl) | Int, Int    |
+| `remove(Range)`               | remove range                          | Range       |
+| `removeLast()`                | remove last element                   |             |
+| `removeLast(n)`               | remove n last elements                | Int         |
+| `contains(element)`           | check the element is in the list (1)  |             |
+| `[index]`                     | get or set element at index           | Int         |
+| `[Range]`                     | get slice of the array (copy)         | Range       |
+| `+=`                          | append element(s)                     | List or Obj |
 
 (1)
-: end-inclisiveness allows to use negative indexes to, for exampe, remove several last elements, like `list.removeRangeInclusive(-2, -1)` will remove two last elements.
+: optimized implementation that override `Array` one
+
+(2)
+: `+=` append either a single element, or all elements if the List or other Iterable
+instance is appended. If you want to append an Iterable object itself, use `add` instead.
+
+It inherits from [Iterable] too.
+
+## Member inherited from Array
+
+| name             | meaning                        | type  |
+|------------------|--------------------------------|-------|
+| `last`           | last element (throws if empty) |       |
+| `lastOrNull`     | last element or null           |       |
+| `lastIndex`      |                                | Int   |
+| `indices`        | range of indexes               | Range |
+| `contains(item)` | test that item is in the list  |       |
+
+(1)
+: end-inclisiveness allows to use negative indexes to, for exampe, remove several last elements, like
+`list.removeRangeInclusive(-2, -1)` will remove two last elements.
 
 
-# Notes
-
-Could be rewritten using array as a class but List as the interface
+[Range]: Range.md
+[Iterable]: Iterable.md

docs/Map.md

@@ -0,0 +1,109 @@
+# Map
+
+Map is a mutable collection of key-value pars, where keys are unique. Maps could be created with
+constructor or `.toMap` methods. When constructing from a list, each list item must be a [Collection] with exactly 2 elements, for example, a [List].
+
+Constructed map instance is of class `Map` and implements `Collection` (and therefore `Iterable`)
+
+    val map = Map( ["foo", 1], ["bar", "buzz"] )
+    assert(map is Map)
+    assert(map.size == 2)
+    assert(map is Iterable)
+    >>> void
+
+Map keys could be any objects (hashable, e.g. with reasonable hashCode, most of standard types are). You can access elements with indexing operator:
+
+    val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
+    assert( map["bar"] == "buzz")
+    assert( map[42] == "answer" )
+    assertThrows { map["nonexistent"] }
+    assert( map.getOrNull(101) == null )
+    assert( map.getOrPut(911) { "nine-eleven" } == "nine-eleven" )
+    // now 91 entry is set:
+    assert( map[911] == "nine-eleven" )
+    map["foo"] = -1
+    assert( map["foo"] == -1)
+    >>> void
+
+To remove item from the collection. use `remove`. It returns last removed item or null. Be careful if you 
+hold nulls in the map - this is not a recommended practice when using `remove` returned value. `clear()` 
+removes all.
+
+    val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
+    assertEquals( 1, map.remove("foo") )
+    assert( map.getOrNull("foo") == null)
+    assert( map.size == 2 )
+    map.clear()
+    assert( map.size == 0 )
+    >>> void
+
+Map implements [contains] method that checks _the presence of the key_ in the map:
+
+    val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
+    assert( "foo" in map )
+    assert( "answer" !in map )
+    >>> void
+
+To iterate maps it is convenient to use `keys` method that returns [Set] of keys (keys are unique:
+
+    val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
+    for( k in map.keys ) println(map[k])
+    >>> 1
+    >>> buzz
+    >>> answer
+    >>> void
+
+Or iterate its key-value pairs that are instances of [MapEntry] class:
+
+    val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
+    for( entry in map ) {
+        println("map[%s] = %s"(entry.key, entry.value))
+    }
+    void
+    >>> map[foo] = 1
+    >>> map[bar] = buzz
+    >>> map[42] = answer
+    >>> void
+
+There is a shortcut to use `MapEntry` to create maps: operator `=>` which creates `MapEntry`:
+
+    val entry = "answer" => 42
+    assert( entry is MapEntry )
+    >>> void
+
+And you can use it to construct maps:
+
+    val map = Map( "foo" => 1, "bar" => 22)
+    assertEquals(1, map["foo"])
+    assertEquals(22, map["bar"])
+    >>> void
+
+Or use `.toMap` on anything that implements [Iterable] and which elements implements [Array] with 2 elements size, for example, `MapEntry`:
+
+    val map = ["foo" => 1, "bar" => 22].toMap()
+    assert( map is Map )
+    assertEquals(1, map["foo"])
+    assertEquals(22, map["bar"])
+    >>> void
+
+
+It is possible also to get values as [List] (values are not unique):
+
+    val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
+    assertEquals(map.values, [1, "buzz", "answer"] )
+    >>> void
+
+Map could be tested to be equal: when all it key-value pairs are equal, the map
+is equal.
+
+    val m1 = Map(["foo", 1])
+    val m2 = Map(["foo", 1])
+    val m3 = Map(["foo", 2])
+    assert( m1 == m2 )
+    // but the references are different:
+    assert( m1 !== m2 )
+    // different maps:
+    assert( m1 != m3 )
+    >>> void
+
+[Collection](Collection.md)

docs/OOP.md

@@ -1,6 +1,168 @@
 # OO implementation in Lyng
 
-Basic principles:
+## Declaration 
+
+The class clause looks like
+
+    class Point(x,y)
+    assert( Point is Class ) 
+    >>> void
+
+It creates new `Class` with two fields. Here is the more practical sample:
+
+    class Point(x,y) {
+        fun length() { sqrt(x*x + y*y) } 
+    }
+
+    val p = Point(3,4)
+    assert(p is Point)
+    assertEquals(5, p.length())
+    
+    // we can access the fields:
+    assert( p.x == 3 )
+    assert( p.y == 4 )
+    
+    // we can assign new values to fields:
+    p.x = 1
+    p.y = 1
+    assertEquals(sqrt(2), p.length())
+    >>> void
+
+
+Let's see in details. The statement `class Point(x,y)` creates a class,
+with two field, which are mutable and publicly visible.`(x,y)` here
+is the [argument list], same as when defining a function. All together creates a class with
+a _constructor_ that requires two parameters for fields. So when creating it with
+`Point(10, 20)` we say _calling Point constructor_ with these parameters.
+
+Form now on `Point` is a class, it's type is `Class`, and we can create instances with it as in the
+example above.
+
+Class point has a _method_, or a _member function_ `length()` that uses its _fields_ `x` and `y` to
+calculate the magnitude. Length is called
+
+### default values in constructor
+
+Constructor arguments are the same as function arguments except visibility
+statements discussed later, there could be default values, ellipsis, etc.
+
+    class Point(x=0,y=0) 
+    val p = Point()
+    assert( p.x == 0 && p.y == 0 )
+    >>> void
+
+## Methods
+
+Functions defined inside a class body are methods, and unless declared
+`private` are available to be called from outside the class:
+
+    class Point(x,y) {
+        // public method declaration:
+        fun length() { sqrt(d2()) }
+
+        // private method:
+        private fun d2() {x*x + y*y}
+    }
+    val p = Point(3,4)
+    // private called from inside public: OK
+    assertEquals( 5, p.length() )
+    // but us not available directly
+    assertThrows { p.d2() }
+    void
+    >>> void
+
+## fields and visibility
+
+It is possible to add non-constructor fields:
+
+    class Point(x,y) {
+        fun length() { sqrt(x*x + y*y) } 
+    
+        // set at construction time:   
+        val initialLength = length()
+    }
+    val p = Point(3,4)
+    p.x = 3
+    p.y = 0
+    assertEquals( 3, p.length() )
+    // but initial length could not be changed after as declard val:
+    assert( p.initialLength == 5 )
+    >>> void
+
+### Mutable fields
+
+Are declared with var
+
+    class Point(x,y) {
+        var isSpecial = false
+    }
+    val p = Point(0,0)
+    assert( p.isSpecial == false )
+
+    p.isSpecial = true
+    assert( p.isSpecial == true )
+    >>> void
+
+### Private fields
+
+Private fields are visible only _inside the class instance_:
+
+    class SecretCounter {
+        private var count = 0
+        
+        fun increment() {
+            count++
+            void // hide counter
+        }
+        
+        fun isEnough() {
+            count > 10
+        }
+    }
+    val c = SecretCounter()
+    assert( c.isEnough() == false )
+    assert( c.increment() == void )
+    for( i in 0..10 ) c.increment()
+    assert( c.isEnough() )
+
+    // but the count is not available outside:
+    assertThrows { c.count }
+    void
+    >>> void
+
+It is possible to provide private constructor parameters so they can be
+set at construction but not available outside the class:
+
+    class SecretCounter(private var count = 0) {
+        // ...
+    }
+    val c = SecretCounter(10)
+    assertThrows { c.count }
+    void
+    >>> void
+
+## Default class methods
+
+In many cases it is necessary to implement custom comparison and `toString`, still
+each class is provided with default implementations:
+
+- default toString outputs class name and its _public_ fields.
+- default comparison compares compares all public fields in order of appearance.
+
+For example, for our class Point:
+
+    class Point(x,y)
+    assert( Point(1,2) == Point(1,2) )
+    assert( Point(1,2) !== Point(1,2) )
+    assert( Point(1,2) != Point(1,3) )
+    assert( Point(1,2) < Point(2,2) )
+    assert( Point(1,2) < Point(1,3) )
+    Point(1,1+1)
+    >>> Point(x=1,y=2)
+
+# Theory
+
+## Basic principles:
 
 - Everything is an instance of some class
 - Every class except Obj has at least one parent
@@ -71,41 +233,6 @@ Regular methods are called on instances as usual `instance.method()`. The method
 2. parents method: no guarantee but we enumerate parents in order of appearance;
 3. possible extension methods (scoped)
 
-# Defining a new class
-
-The class is a some data record with named fields and fixed order, in fact. To define a class,
-just Provide a name and a record like this:
-
-    // creating new class with main constructor
-    // with all fields public and mutable:
-
-    struct Point(x,y)
-    assert( Point is Class )
-    
-    // now we can create instance
-    val p1 = Point(3,4)
-
-    // is is of the newly created type:
-    assert( p1 is Point )
-
-    // we can read and write its fields:
-    assert( p1.x == 3 )
-    assert( p1.y == 4 )
-
-    p1.y++ 
-    assert( p1.y == 5 )
-
-    >>> void
-    
-Let's see in details. The statement `struct Point(x,y)` creates a struct, or public class,
-with two field, which are mutable and publicly visible, because it is _struct_. `(x,y)` here 
-is the [argument list], same as when defining a function. All together creates a class with
-a _constructor_ that requires two parameters for fields. So when creating it with
-`Point(10, 20)` we say _calling Point constructor_ with these parameters.
-
-Such declaration is identical to `class Point(var x,var y)` which does exactly the same.
-
-
 TBD
 
 [argument list](declaring_arguments.md)

docs/Set.md

@@ -0,0 +1,94 @@
+# List built-in class
+
+Mutable set of any objects: a group of different objects, no repetitions.
+Sets are not ordered, order of appearance does not matter.
+
+    val set = Set(1,2,3, "foo")
+    assert( 1 in set )
+    assert( "foo" in set)
+    assert( "bar" !in set)
+    >>> void
+
+## Set is collection and therefore [Iterable]:
+
+    assert( Set(1,2) is Set)
+    assert( Set(1,2) is Iterable)
+    assert( Set(1,2) is Collection)
+    >>> void
+
+So it supports all methods from [Iterable]; set is not, though, an [Array] and has
+no indexing. Use [set.toList] as needed.
+
+## Set operations
+
+    // Union
+    assertEquals( Set(1,2,3,4), Set(3, 1) + Set(2, 4))
+
+    // intersection
+    assertEquals( Set(1,4), Set(3, 1, 4).intersect(Set(2, 4, 1)) )
+    // or simple
+    assertEquals( Set(1,4), Set(3, 1, 4) * Set(2, 4, 1) )
+
+    // To find collection elements not present in another collection, use the 
+    // subtract() or `-`:
+    assertEquals( Set( 1, 2), Set(1, 2, 4, 3) - Set(3, 4))
+
+    >>> void
+
+## Adding elements
+
+    var s = Set()
+    s += 1
+    assertEquals( Set(1), s)
+    
+    s += [3, 3, 4]
+    assertEquals( Set(3, 4, 1), s)
+    >>> void
+
+## Removing elements
+
+List is mutable, so it is possible to remove its contents. To remove a single element
+by index use:
+
+    var s = Set(1,2,3)
+    s.remove(2)
+    assertEquals( s, Set(1,3) )
+
+    s = Set(1,2,3)
+    s.remove(2,1)
+    assertEquals( s, Set(3) )
+    >>> void
+
+Note that `remove` returns true if at least one element was actually removed and false
+if the set has not been changed.
+
+## Comparisons and inclusion
+
+Sets are only equal when contains exactly same elements, order, as was said, is not significant:
+
+    assert( Set(1, 2) == Set(2, 1) )
+    assert( Set(1, 2, 2) == Set(2, 1) )
+    assert( Set(1, 3) != Set(2, 1) )
+    assert( 1 in Set(5,1))
+    assert( 10 !in Set(5,1))
+    >>> void
+
+## Members
+
+| name                | meaning                              | type  |
+|---------------------|--------------------------------------|-------|
+| `size`              | current size                         | Int   |
+| `+=`                | add one or more elements             | Any   |
+| `+`, `union`         | union sets                           | Any   |
+| `-`, `subtract`     | subtract sets                        | Any   |
+| `*`, `intersect`    | subtract sets                        | Any   |
+| `remove(items...)`  | remove one or more items             | Range |
+| `contains(element)` | check the element is in the list (1) |       |
+
+(1)
+: optimized implementation that override `Iterable` one
+
+Also, it inherits methods from [Iterable].
+
+
+[Range]: Range.md

docs/advanced_topics.md

@@ -86,4 +86,28 @@ Lambda functions remember their scopes, so it will work the same as previous:
     val c = createLambda()
     println(c)
     >> 1
-    >> void
+    >> void
+
+# Elements of functional programming
+
+With ellipsis and splats you can create partial functions, manipulate
+arguments list in almost arbitrary ways. For example:
+
+    // Swap first and last arguments for call
+
+    fun swap_args(first, others..., last, f) { 
+        f(last, ...others, first) 
+    }
+
+    fun glue(args...) {
+        var result = ""
+        for( a in args ) result += a
+    }
+
+    assertEquals( 
+        "4231", 
+        swap_args( 1, 2, 3, 4, glue)
+    )
+    >>> void
+
+,

docs/declaring_arguments.md

@@ -1,7 +1,7 @@
 # Declaring arguments in Lyng
 
 It is a common thing that occurs in many places in Lyng, function declarations, 
-lambdas, struct and class declarations.
+lambdas and class declarations.
 
 ## Regular
 

docs/development/including_modules.md

@@ -39,22 +39,5 @@ We can just put the code into the module code:
 
 ## class initialization
 
-    class foo {
-        
-        private static var instanceCounter = 0
-        
-        val instanceId = instanceCounter
-        
-        fun close() {
-            instanceCounter--
-        }
-
-        // instance initializatino could be as this:
-        if( instanceId > 100 )
-            throw Exception("Too many instances")
-
-        static {
-            // static, one-per-class initializer could be posted here
-            instanceCounter = 1
-        }
-    }
+already done using `ObjInstance` class and instance-bound context with local
+context stored in ObjInstance and class constructor statement in ObjClass.

docs/exceptions_handling.md

@@ -0,0 +1,145 @@
+# Exceptions handling
+
+Exceptions are widely used in modern programming languages, so
+they are implemented also in Lyng and in the most complete way.
+
+# Exception classes
+
+Exceptions are throwing instances of some class that inherits `Exception`
+across the code. Below is the list of built-in exceptions. Note that
+only objects that inherit `Exception` can be thrown. For example:
+
+    assert( IllegalArgumentException() is Exception)
+    >>> void
+
+# Try statement: catching exceptions
+
+There general pattern is:
+
+```
+try_statement = try_clause, [catch_clause, ...], [finally_clause] 
+
+try_clause = "try", "{", statements, "}"
+
+catch_clause = "catch", [(full_catch | shorter_catch)], "{", statements "}"
+
+full_catch = "(", catch_var, ":", exception_class [, excetpion_class...], ")
+
+shorter_catch = "(", catch_var, ")"
+
+finally_clause = "{", statements, "}"
+```
+
+Let's in details.
+
+## Full catch block:
+
+    val result = try {
+        throw IllegalArgumentException("the test")
+    }
+    catch( x: IndexOutOfBoundsException, IllegalArgumentException) {
+        x.message
+    }
+    catch(x: Exception) {
+        "bad"
+    }
+    assertEquals(result, "the test")
+    >>> void
+
+Because our exception is listed in a first catch block, it is processed there.
+
+The full form allow a single catch block to process exceptions with specified classes and bind actual caught object to
+the given variable. This is most common and well known form, implemented like this or similar in many other languages,
+like Kotlin, Java or C++.
+
+## Shorter form
+
+When you want to catch _all_ the exceptions, you should write `catch(e: Exception)`,
+but it is somewhat redundant, so there is simpler variant:
+
+    val sample2 = try {
+        throw IllegalArgumentException("sample 2")
+    }
+    catch(x) {
+        x.message
+    }
+    assertEquals( sample2, "sample 2" )
+    >>> void
+
+But well most likely you will find default variable `it`, like in Kotlin, more than enough
+to catch all exceptions to, then you can write it even shorter:
+
+    val sample2 = try {
+        throw IllegalArgumentException("sample 3")
+    }
+    catch {
+        it.message
+    }
+    assertEquals( sample2, "sample 3" )
+    >>> void
+
+You can even check the type of the `it` and create more convenient and sophisticated processing logic. Such approach is
+used, for example, in Scala.
+
+## finally block
+
+If `finally` block present, it will be executed after body (until first exception)
+and catch block, if any will match. finally statement is executed even if the
+exception will be thrown and not caught locally. It does not alter try/catch block result:
+
+    try {
+    }
+    finally {
+        println("called finally")
+    }
+    >>> called finally
+    >>> void
+
+- and yes, there could be try-finally block, no catching, but perform some guaranteed cleanup.
+
+# Conveying data with exceptions
+
+The simplest way is to provide exception string and `Exception` class:
+
+    try {
+        throw Exception("this is my exception")
+    }
+    catch {
+        it.message
+    }
+    >>> "this is my exception"
+
+This way, in turn, can also be shortened, as it is overly popular:
+
+    try {
+        throw "this is my exception"
+    }
+    catch {
+        it.message
+    }
+    >>> "this is my exception"
+
+The trick, though, works with strings only, and always provide `Exception` instances, which is good for debugging but
+most often not enough.
+
+# Custom error classes
+
+_this functionality is not yet released_
+
+# Standard exception classes
+
+| class                      | notes                                                 |
+|----------------------------|-------------------------------------------------------|
+| Exception                  | root of al throwable objects                          |
+| NullReferenceException       |                                                       |
+| AssertionFailedException   |                                                       | 
+| ClassCastException         |                                                       |
+| IndexOutOfBoundsException  |                                                       |
+| IllegalArgumentException   |                                                       | 
+| IllegalAssignmentException | assigning to val, etc.                                |
+| SymbolNotDefinedException  |                                                       |
+| IterationEndException      | attempt to read iterator past end, `hasNext == false` |
+| AccessException            | attempt to access private members or like             |
+| UnknownException           | unexpected kotlin exception caught                    |
+|                            |                                                       |
+

docs/samples/sum.lyng

@@ -0,0 +1,26 @@
+/*
+    Calculate the limit of Sum( f(n) )
+    until it reaches asymptotic limit 0.00001% change
+
+    return null or found limit
+*/
+fun findSumLimit(f) {
+    var sum = 0.0
+    for( n in 1..1000000 ) {
+        val s0 = sum
+        sum += f(n)
+        if( abs(sum - s0) / abs(sum) < 1.0e-6 ) {
+            println("limit reached after "+n+" rounds")
+            break sum
+        }
+        n++
+    }
+    else {
+        println("limit not reached")
+        null
+    }
+}
+
+val limit = findSumLimit { n -> 1.0/n/n }
+
+println("Result: "+limit)

docs/samples/сумма_ряда.lyng.md

@@ -0,0 +1,53 @@
+# Пример расчета суммы ряда
+
+Рассмотрим как можно посчитать предел суммы ряда на lyng. Для наивной реализации
+представим что у нас есть функция рассчитывающая n-й член ряда. Тогда мы можем 
+считать сумму до тех пор, пока отклонение при расчете следующего члена не станет
+меньше чем заданная погрешность:
+
+    fun сумма_ряда(x, погрешность=0.0001, f) {
+        var сумма = 0
+        for( n in 1..100000) {
+            val следующая_сумма = сумма + f(x, n)
+            if( n > 1 && abs(следующая_сумма - сумма) < погрешность )
+                break следующая_сумма
+            сумма = следующая_сумма
+        }
+        else null
+    }
+
+Для проверки можно посчитать на хорошо известном ряду Меркатора
+
+$$ \ln(1+x)=x-{\dfrac {x^{2}}{2}}+{\dfrac {x^{3}}{3}}-\cdots =\sum \limits _{n=0}^{\infty }{\dfrac {(-1)^{n}x^{n+1}}{(n+1)}}=\sum \limits _{n=1}^{\infty }{\dfrac {(-1)^{n-1}x^{n}}{n}} $$
+
+Который в нашем случае для точки $ x = 1 $ можно записать так:
+
+    val x = сумма_ряда(1) { x, n -> 
+        val sign = if( n % 2 == 1 ) 1 else -1
+        sign * pow(x, n) / n
+    }
+
+Проверим:
+    
+    assert( x - ln(2) < 0.001 )
+
+В нашем примере есть изъян - погрешность вычисляется примитивно: `abs(следующая_сумма - сумма) < погрешность`, что совершенно неверно, если значения малы. Значительно более корректно вычислять погрешность, нормированную на диапазон сравниваемых величин:
+
+
+    fun погрешность(x0, x1) {
+        abs( x1 - x0 ) / (abs( x1 + x0 ) / 2.0)
+    }
+    // относительная погрешность одинакова и в разных диапазонах
+    assertEquals( погрешность(5,6), погрешность(0.005,0.006))
+
+Теперь мы могли бы написать более корректное сравнение для вещественных
+
+    // расхождение не больше 1% или сколько укажете:
+    fun почти_равны(a,b,epsilon=0.01) { 
+        погрешность(a,b) <= epsilon 
+    }
+    assert( почти_равны( 0.0005, 0.000501 ) )
+
+Во многих случаях вычисление $n+1$ члена значительно проще cчитается от предыдущего члена, в нашем случае это можно было бы записать через итератор, что мы вскоре добавим.
+
+(продолжение следует)

docs/tutorial.md

@@ -12,11 +12,10 @@ In other word, the code usually works as expected when you see it. So, nothing u
 __Other documents to read__ maybe after this one:
 
 - [Advanced topics](advanced_topics.md), [declaring arguments](declaring_arguments.md)
-- [OOP notes](OOP.md)
+- [OOP notes](OOP.md), [exception handling](exceptions_handling.md)
 - [math in Lyng](math.md)
-- Some class references: [List], [Real], [Range], [Iterable], [Iterator]
-- Some samples: [combinatorics](samples/combinatorics.lyng.md)
-    See [samples folder](samples)
+- Some class references: [List], [Set], [Map], [Real], [Range], [Iterable], [Iterator]
+- Some samples: [combinatorics](samples/combinatorics.lyng.md), national vars and loops: [сумма ряда](samples/сумма_ряда.lyng.md). More at [samples folder](samples)
 
 # Expressions
 
@@ -119,6 +118,109 @@ These operators return rvalue, unmodifiable.
 
 ## Assignment return r-value!
 
+Naturally, assignment returns its value:
+
+    var x
+    x = 11
+    >>> 11
+
+rvalue means you cant assign the result if the assignment
+
+    var x
+    assertThrows { (x = 11) = 5 }
+    void
+    >>> void
+
+This also prevents chain assignments so use parentheses:
+
+    var x
+    var y
+    x = (y = 1)
+    >>> 1
+
+## Nullability
+
+When the value is `null`, it might throws `NullReferenceException`, the name is somewhat a tradition. To avoid it
+one can check it against null or use _null coalescing_. The null coalescing means, if the operand (left) is null,
+the operation won't be performed and the result will be null. Here is the difference:
+
+    val ref = null
+    assertThrows {  ref.field }
+    assertThrows {  ref.method() }
+    assertThrows {  ref.array[1] }
+    assertThrows {  ref[1] }
+    assertThrows {  ref() }
+    
+    assert( ref?.field == null )
+    assert( ref?.method() == null )
+    assert( ref?.array?[1] == null )
+    assert( ref?[1] == null )
+    assert( ref?() == null )
+    >>> void
+
+There is also "elvis operator", null-coalesce infix operator '?:' that returns rvalue if lvalue is `null`:
+
+    null ?: "nothing"
+    >>> "nothing"
+
+## Utility functions
+
+The following functions simplify nullable values processing and
+allow to improve code look and readability. There are borrowed from Kotlin:
+
+### let 
+
+`value.let {}` passes to the block value as the single parameter (by default it is assigned to `it`) and return block's returned value. It is useful dealing with null or to
+get a snapshot of some externally varying value, or with `?.` to process nullable value in a safe manner:
+
+    // this state is changed from parallel processes
+    class GlobalState(nullableParam)
+    
+    val state = GlobalState(null)
+
+    fun sample() {
+        state.nullableParam?.let { "it's not null: "+it} ?: "it's null"
+    }
+    assertEquals(sample(), "it's null")
+    state.nullableParam = 5
+    assertEquals(sample(), "it's not null: 5")
+    >>> void
+
+This is the same as:
+
+    fun sample() {
+        val it = state.nullableParam
+        if( it != null )  "it's not null: "+it else "it's null"
+    }
+
+The important is that nullableParam got a local copy that can't be changed from any
+parallel thread/coroutine. Remember: Lyng _is __not__ a single-threaded language_.
+
+## Also
+
+Much like let, but it does not alter returned value:
+
+    assert( "test".also { println( it + "!") } == "test" )
+    >>> test!
+    >>> void
+
+While it is not altering return value, the source object could be changed:
+
+    class Point(x,y)
+    val p = Point(1,2).also { it.x++ }
+    assertEquals(p.x, 2)
+    >>> void
+
+## apply
+
+It works much like `also`, but is executed in the context of the source object:
+
+    class Point(x,y)
+    // see the difference: apply changes this to newly created Point:
+    val p = Point(1,2).apply { x++; y++ }
+    assertEquals(p, Point(2,3))
+    >>> void
+
 ## Math
 
 It is rather simple, like everywhere else:
@@ -470,64 +572,97 @@ To add elements to the list:
     assert( x == [1, 2, 3, "the", "end"])
     >>> void
 
-Self-modifying concatenation by `+=` also works:
+Self-modifying concatenation by `+=` also works (also with single elements):
 
     val x = [1, 2]
     x += [3, 4]
-    assert( x == [1, 2, 3, 4])
+    x += 5
+    assert( x == [1, 2, 3, 4, 5])
     >>> void
 
-You can insert elements at any position using `addAt`:
+You can insert elements at any position using `insertAt`:
 
     val x = [1,2,3]
-    x.addAt(1, "foo", "bar")
+    x.insertAt(1, "foo", "bar")
     assert( x == [1, "foo", "bar", 2, 3])
     >>> void
 
 Using splat arguments can simplify inserting list in list:
 
     val x = [1, 2, 3]
-    x.addAt( 1, ...[0,100,0])
+    x.insertAt( 1, ...[0,100,0])
     x
     >>> [1, 0, 100, 0, 2, 3]
 
-Using negative indexes can insert elements as offset from the end, for example:
-
-    val x = [1,2,3]
-    x.addAt(-1, 10)
-    x
-    >>> [1, 2, 10, 3]
 
 Note that to add to the end you still need to use `add` or positive index of the after-last element:
 
     val x = [1,2,3]
-    x.addAt(3, 10)
+    x.insertAt(3, 10)
     x
     >>> [1, 2, 3, 10]
 
+but it is much simpler, and we recommend to use '+='
+
+    val x = [1,2,3]
+    x += 10
+    >>> [1, 2, 3, 10]
+
 ## Removing list items
 
     val x = [1, 2, 3, 4, 5]
     x.removeAt(2)
     assert( x == [1, 2, 4, 5])
     // or remove range (start inclusive, end exclusive):
-    x.removeRangeInclusive(1,2)    
+    x.removeRange(1..2)    
     assert( x == [1, 5])
     >>> void
 
-Again, you can use negative indexes. For example, removing last elements like:
+There is a shortcut to remove the last elements:
 
     val x = [1, 2, 3, 4, 5]
 
     // remove last:
-    x.removeAt(-1)
+    x.removeLast()
     assert( x == [1, 2, 3, 4])
     
     // remove 2 last:
-    x.removeRangeInclusive(-2,-1)
-    assert( x == [1, 2])
+    x.removeLast(2)
+    assertEquals( [1, 2], x)
     >>> void
 
+You can get ranges to extract a portion from a list:
+
+    val list = [1, 2, 3, 4, 5]
+    assertEquals( [1,2,3], list[..2])
+    assertEquals( [1,2,], list[..<2])
+    assertEquals( [4,5], list[3..])
+    assertEquals( [2,3], list[1..2])
+    assertEquals( [2,3], list[1..<3])
+    >>> void
+
+# Sets
+
+Set are unordered collection of unique elements, see [Set]. Sets are [Iterable] but have no indexing access.
+
+    assertEquals( Set(3, 2, 1), Set( 1, 2, 3))
+    assert( 5 !in Set(1, 2, 6) )
+    >>> void
+
+Please see [Set] for detailed description.
+
+# Maps
+
+Maps are unordered collection of key-value pairs, where keys are unique. See [Map] for details. Map also
+are [Iterable]:
+
+    val m = Map( "foo" => 77, "bar" => "buzz" )
+    assertEquals( m["foo"], 77 )
+    >>> void
+
+Please see [Map] reference for detailed description on using Maps.
+
+
 # Flow control operators
 
 ## if-then-else
@@ -553,18 +688,101 @@ Or, more neat:
     >>> just 3
     >>> void
 
+## When
+
+It is very much like the kotlin's:
+
+    fun type(x) {
+        when(x) {
+            in 'a'..'z', in 'A'..'Z' -> "letter"
+            in '0'..'9' -> "digit"
+            '$' -> "dollar"
+            "EUR" -> "crap"
+            in ['@', '#', '^'] -> "punctuation1"
+            in "*&.," -> "punctuation2"
+            else -> "unknown"
+        }
+    }
+    assertEquals("digit", type('3'))
+    assertEquals("dollar", type('$'))
+    assertEquals("crap", type("EUR"))
+    >>> void
+
+Notice, several conditions can be grouped with a comma.
+Also, you can check the type too:
+
+    fun type(x) {
+        when(x) {
+            "42", 42 -> "answer to the great question"
+            is Real, is Int -> "number"
+            is String -> {
+                for( d in x ) {
+                    if( d !in '0'..'9' ) 
+                        break "unknown"
+                }
+                else "number"
+            }
+        }
+    }
+    assertEquals("number", type(5))
+    assertEquals("number", type("153"))
+    assertEquals("number", type(π/2))
+    assertEquals("unknown", type("12%"))
+    assertEquals("answer to the great question", type(42))
+    assertEquals("answer to the great question", type("42"))
+    >>> void
+
+### supported when conditions:
+
+#### Contains: 
+
+You can thest that _when expression_ is _contained_, or not contained, in some object using `in container` and `!in container`. The container is any object that provides `contains` method, otherwise the runtime exception will be thrown.
+
+Typical builtin types that are containers (e.g. support `conain`):
+
+| class      | notes                                      |
+|------------|--------------------------------------------|
+| Collection | contains an element (1)                    |
+| Array      | faster maybe that Collection's             |
+| List       | faster than Array's                        |
+| String     | character in string or substring in string |
+| Range      | object is included in the range (2)        |
+
+(1)
+: Iterable is not the container as it can be infinite
+
+(2)
+: Depending on the inclusivity and open/closed range parameters. BE careful here: String range is allowed, but it is usually not what you expect of it:
+
+    assert( "more" in "a".."z") // string range ok
+    assert( 'x' !in "a".."z") // char in string range: probably error
+    assert( 'x' in 'a'..'z') // character range: ok
+    assert( "x" !in 'a'..'z') // string in character range: could be error
+    >>> void
+
+So we recommend not to mix characters and string ranges; use `ch in str` that works
+as expected:
+
+    "foo" in "foobar"
+    >>> true
+
+and also character inclusion:
+
+    'o' in "foobar"
+    >>> true
+
 ## while
 
-Regular pre-condition while loop, as expression, loop returns it's last line result:
+Regular pre-condition while loop, as expression, loop returns the last expression as everything else:
 
     var count = 0
-    while( count < 5 ) {
-        count++
-        count * 10
-    }
-    >>> 50
+    val result = while( count < 5 ) count++
+    result
+    >>> 4
 
-We can break as usual:
+Notice it _is 4 because when count became 5, the loop body was not executed!_.
+
+We can break while as usual:
 
     var count = 0
     while( count < 5 ) {
@@ -683,6 +901,36 @@ So the returned value, as seen from diagram could be one of:
 - value returned from the `else` clause, of the loop was not broken
 - value returned from the last execution of loop body, if there was no `break` and no `else` clause.
 
+## do-while loops
+
+There works exactly as while loops but the body is executed prior to checking the while condition:
+
+    var i = 0
+    do { i++ } while( i < 1 )
+    i
+    >>> 1
+
+The important feature of the do-while loop is that the condition expression is
+evaluated on the body scope, e.g., variables, intruduced in the loop body are
+available in the condition:
+
+    do {
+        var continueLoop = false
+        "OK"
+    } while( continueLoop )
+    >>> "OK"
+
+This is sometimes convenient when condition is complex and has to be calculated inside the loop body. Notice the value returning by the loop:
+
+    fun readLine() { "done: result" }
+    val result = do {
+        val line = readLine()
+    } while( !line.startsWith("done:") )
+    result.drop(6)
+    >>> "result"
+
+Suppose readLine() here reads some stream of lines.
+
 
 ## For loops
 
@@ -724,6 +972,62 @@ We can use labels too:
     assert( search(["hello", "world"], 'z') == null)
     >>> void
 
+# Exception handling
+
+Very much like in Kotlin. Try block returns its body block result, if no exception was cauht, or the result from the catch block that caught the exception:
+
+    var error = "not caught"
+    var finallyCaught = false
+    val result = try {
+        throw IllegalArgumentException()
+        "invalid"
+    }
+    catch(nd: SymbolNotDefinedException) {
+        error = "bad catch"
+    }
+    catch(x: IllegalArgumentException) {
+        error = "no error"
+        "OK"
+    }
+    finally {
+        // finally does not affect returned value
+        "too bad"
+    }
+    assertEquals( "no error", error)
+    assertEquals( "OK", result)
+    >>> void
+
+There is shorter form of catch block when you want to catch any exception:
+
+    var caught = null
+    try {
+        throw IllegalArgumentException()
+    }
+    catch(t) { // same as catch(t: Exception), but simpler
+        caught = t
+    }
+    assert( caught is IllegalArgumentException )
+    >>> void
+
+And even shortest, for the Lying lang tradition, missing var is `it`:
+
+    var caught = null
+    try {
+        throw IllegalArgumentException()
+    }
+    catch { // same as catch(it: Exception), but simpler
+        caught = it
+    }
+    assert( caught is IllegalArgumentException )
+    >>> void
+
+It is possible to catch several exceptions in the same block too, use 
+`catch( varName: ExceptionClass1, ExceptionClass2)`, etc, use short form of throw and
+many more.
+
+- see [exception handling](exceptions_handling.md) for detailed exceptions tutorial and reference.
+
+
 # Self-assignments in expression
 
 There are auto-increments and auto-decrements:
@@ -792,7 +1096,7 @@ See [Ranges](Range.md) for detailed documentation on it.
 
     // single line comment
     var result = null // here we will store the result
-    >>> void
+    >>> null
 
 # Integral data types
 
@@ -838,10 +1142,84 @@ Are the same as in string literals with little difference:
 
 ## String details
 
+Strings are arrays of Unicode characters. It can be indexed, and indexing will
+return a valid Unicode character at position. No utf hassle:
+
+    "Парашют"[5]
+    >>> 'ю'
+
+Its length is, of course, in characters:
+
+    "разум".length
+    >>> 5
+
+And supports growing set of kotlin-borrowed operations, see below, for example:
+
+    assertEquals("Hell", "Hello".dropLast(1))
+    >>> void
+
+To format a string use sprintf-style modifiers like:
+
+    val a = "hello"
+    val b = 11
+    assertEquals( "hello:11", "%s:%d"(a, b) )
+    assertEquals( " hello:    11", "%6s:%6d"(a, b) )
+    assertEquals( "hello :11    ", "%-6s:%-6d"(a, b) )
+    >>> void
+
+List of format specifiers closely resembles C sprintf() one. See [format specifiers](https://github.com/sergeych/mp_stools?tab=readme-ov-file#sprintf-syntax-summary), this is doe using [mp_stools kotlin multiplatform library](https://github.com/sergeych/mp_stools). Currently supported Lyng types are `String`, `Int`, `Real`, `Bool`, the rest are displayed using their `toString()` representation.
+
+This list will be extended.
+
+To get the substring use:
+
+    assertEquals("pult", "catapult".takeLast(4))
+    assertEquals("cat", "catapult".take(3))
+    assertEquals("cat", "catapult".dropLast(5))
+    assertEquals("pult", "catapult".drop(4))
+    >>> void
+
+And to get a portion you can slice it with range as the index:
+
+    assertEquals( "tap", "catapult"[ 2 .. 4 ])
+    assertEquals( "tap", "catapult"[ 2 ..< 5 ])
+    >>> void
+
+Open-ended ranges could be used to get start and end too:
+
+    assertEquals( "cat", "catapult"[ ..< 3 ])
+    assertEquals( "cat", "catapult"[ .. 2 ])
+    assertEquals( "pult", "catapult"[ 4.. ])
+    >>> void
+
 ### String operations
 
 Concatenation is a `+`: `"hello " + name` works as expected. No confusion.
 
+Typical set of String functions includes:
+
+| fun/prop           | description / notes                                        |
+|--------------------|------------------------------------------------------------|
+| lower()            | change case to unicode upper                               |
+| upper()            | change case to unicode lower                               |
+| startsWith(prefix) | true if starts with a prefix                               |
+| endsWith(prefix)   | true if ends with a prefix                                 |
+| take(n)            | get a new string from up to n first characters             |
+| takeLast(n)        | get a new string from up to n last characters              |
+| drop(n)            | get a new string dropping n first chars, or empty string   |
+| dropLast(n)        | get a new string dropping n last chars, or empty string    |
+| size               | size in characters like `length` because String is [Array] |
+| (args...)          | sprintf-like formatting, see [string formatting]           |
+| [index]            | character at index                                         | 
+| [Range]            | substring at range                                         |
+| s1 + s2            | concatenation                                              |
+| s1 += s2           | self-modifying concatenation                               |
+
+
+
+
+
+
 ### Literals
 
 String literal could be multiline:
@@ -872,5 +1250,7 @@ See [math functions](math.md). Other general purpose functions are:
 [Iterator]: Iterator.md
 [Real]: Real.md
 [Range]: Range.md
-
-
+[String]: String.md
+[string formatting]: https://github.com/sergeych/mp_stools?tab=readme-ov-file#sprintf-syntax-summary
+[Set]: Set.md
+[Map]: Map.md

happy.py

@@ -1,11 +0,0 @@
-count = 0
-for n1 in range(10):
-    for n2 in range(10):
-        for n3 in range(10):
-            for n4 in range(10):
-                for n5 in range(10):
-                    for n6 in range(10):
-                        if n1 + n2 + n3 == n4 + n5 + n6:
-                            count += 1
-
-print(count)

library/src/commonMain/kotlin/net/sergeych/lyng/Arguments.kt

@@ -1,54 +0,0 @@
-package net.sergeych.lyng
-
-data class ParsedArgument(val value: Statement, val pos: Pos, val isSplat: Boolean = false)
-
-suspend fun Collection<ParsedArgument>.toArguments(context: Context): Arguments {
-    val list = mutableListOf<Arguments.Info>()
-
-    for (x in this) {
-        val value = x.value.execute(context)
-        if (x.isSplat) {
-            when {
-                value is ObjList -> {
-                    for (subitem in value.list) list.add(Arguments.Info(subitem, x.pos))
-                }
-
-                value.isInstanceOf(ObjIterable) -> {
-                    val i = (value.invokeInstanceMethod(context, "toList") as ObjList).list
-                    i.forEach { list.add(Arguments.Info(it, x.pos)) }
-                }
-
-                else -> context.raiseClassCastError("expected list of objects for splat argument")
-            }
-        } else
-            list.add(Arguments.Info(value, x.pos))
-    }
-    return Arguments(list)
-}
-
-data class Arguments(val list: List<Info>) : Iterable<Obj> {
-
-    data class Info(val value: Obj, val pos: Pos)
-
-    val size by list::size
-
-    operator fun get(index: Int): Obj = list[index].value
-
-    val values: List<Obj>  by lazy { list.map { it.value } }
-
-    fun firstAndOnly(): Obj {
-        if (list.size != 1) throw IllegalArgumentException("Expected one argument, got ${list.size}")
-        return list.first().value
-    }
-
-    companion object {
-        val EMPTY = Arguments(emptyList())
-        fun from(values: Collection<Obj>) = Arguments(values.map { Info(it, Pos.UNKNOWN) })
-    }
-
-    override fun iterator(): Iterator<Obj> {
-        return list.map { it.value }.iterator()
-    }
-
-}
-

library/src/commonMain/kotlin/net/sergeych/lyng/ObjClass.kt

@@ -1,153 +0,0 @@
-package net.sergeych.lyng
-
-val ObjClassType by lazy { ObjClass("Class") }
-
-class ObjClass(
-    val className: String,
-    vararg val parents: ObjClass,
-) : Obj() {
-
-    var instanceConstructor: Statement? = null
-
-    val allParentsSet: Set<ObjClass> = parents.flatMap {
-        listOf(it) + it.allParentsSet
-    }.toSet()
-
-    override val objClass: ObjClass by lazy { ObjClassType }
-
-    // members: fields most often
-    private val members = mutableMapOf<String, ObjRecord>()
-
-    override fun toString(): String = className
-
-    override suspend fun compareTo(context: Context, other: Obj): Int = if (other === this) 0 else -1
-
-    override suspend fun callOn(context: Context): Obj {
-        println("callOn $this constructing....")
-        println("on context: $context")
-        val instance = ObjInstance(this)
-        instance.instanceContext = context.copy(newThisObj = instance,args = context.args)
-        if (instanceConstructor != null) {
-            instanceConstructor!!.execute(instance.instanceContext)
-        }
-        return instance
-    }
-
-    fun defaultInstance(): Obj = object : Obj() {
-        override val objClass: ObjClass = this@ObjClass
-    }
-
-    fun createField(
-        name: String,
-        initialValue: Obj,
-        isMutable: Boolean = false,
-        visibility: Compiler.Visibility = Compiler.Visibility.Public,
-        pos: Pos = Pos.builtIn
-    ) {
-        if (name in members || allParentsSet.any { name in it.members } == true)
-            throw ScriptError(pos, "$name is already defined in $objClass or one of its supertypes")
-        members[name] = ObjRecord(initialValue, isMutable, visibility)
-    }
-
-    fun addFn(name: String, isOpen: Boolean = false, code: suspend Context.() -> Obj) {
-        createField(name, statement { code() }, isOpen)
-    }
-
-    fun addConst(name: String, value: Obj) = createField(name, value, isMutable = false)
-
-
-    /**
-     * Get instance member traversing the hierarchy if needed. Its meaning is different for different objects.
-     */
-    fun getInstanceMemberOrNull(name: String): ObjRecord? {
-        members[name]?.let { return it }
-        allParentsSet.forEach { parent -> parent.getInstanceMemberOrNull(name)?.let { return it } }
-        return null
-    }
-
-    fun getInstanceMember(atPos: Pos, name: String): ObjRecord =
-        getInstanceMemberOrNull(name)
-            ?: throw ScriptError(atPos, "symbol doesn't exist: $name")
-}
-
-/**
- * Abstract class that must provide `iterator` method that returns [ObjIterator] instance.
- */
-val ObjIterable by lazy {
-    ObjClass("Iterable").apply {
-
-        addFn("toList") {
-            val result = mutableListOf<Obj>()
-            val iterator = thisObj.invokeInstanceMethod(this, "iterator")
-
-            while (iterator.invokeInstanceMethod(this, "hasNext").toBool())
-                result += iterator.invokeInstanceMethod(this, "next")
-
-
-//        val next = iterator.getMemberOrNull("next")!!
-//        val hasNext = iterator.getMemberOrNull("hasNext")!!
-//        while( hasNext.invoke(this, iterator).toBool() )
-//            result += next.invoke(this, iterator)
-            ObjList(result)
-        }
-
-    }
-}
-
-/**
- * Collection is an iterator with `size`]
- */
-val ObjCollection by lazy {
-    val i: ObjClass = ObjIterable
-    ObjClass("Collection", i)
-}
-
-val ObjIterator by lazy { ObjClass("Iterator") }
-
-class ObjArrayIterator(val array: Obj) : Obj() {
-
-    override val objClass: ObjClass by lazy { type }
-
-    private var nextIndex = 0
-    private var lastIndex = 0
-
-    suspend fun init(context: Context) {
-        nextIndex = 0
-        lastIndex = array.invokeInstanceMethod(context, "size").toInt()
-        ObjVoid
-    }
-
-    companion object {
-        val type by lazy {
-            ObjClass("ArrayIterator", ObjIterator).apply {
-                addFn("next") {
-                    val self = thisAs<ObjArrayIterator>()
-                    if (self.nextIndex < self.lastIndex) {
-                        self.array.invokeInstanceMethod(this, "getAt", (self.nextIndex++).toObj())
-                    } else raiseError(ObjIterationFinishedError(this))
-                }
-                addFn("hasNext") {
-                    val self = thisAs<ObjArrayIterator>()
-                    if (self.nextIndex < self.lastIndex) ObjTrue else ObjFalse
-                }
-            }
-        }
-    }
-}
-
-
-val ObjArray by lazy {
-
-    /**
-     * Array abstract class is a [ObjCollection] with `getAt` method.
-     */
-    ObjClass("Array", ObjCollection).apply {
-        // we can create iterators using size/getat:
-
-        addFn("iterator") {
-            ObjArrayIterator(thisObj).also { it.init(this) }
-        }
-        addFn("isample") { "ok".toObj() }
-    }
-}
-

library/src/commonMain/kotlin/net/sergeych/lyng/ObjInstance.kt

@@ -1,29 +0,0 @@
-package net.sergeych.lyng
-
-class ObjInstance(override val objClass: ObjClass) : Obj() {
-
-    internal val publicFields = mutableSetOf<String>()
-    internal val protectedFields = mutableSetOf<String>()
-
-    internal lateinit var instanceContext: Context
-
-    override suspend fun readField(context: Context, name: String): ObjRecord {
-        return if( name in publicFields ) instanceContext[name]!!
-        else super.readField(context, name)
-    }
-
-    override suspend fun writeField(context: Context, name: String, newValue: Obj) {
-        if( name in publicFields ) {
-            val f = instanceContext[name]!!
-            if( !f.isMutable ) ObjIllegalAssignmentError(context, "can't reassign val $name").raise()
-            if( f.value.assign(context, newValue) == null)
-                f.value = newValue
-        }
-        else super.writeField(context, name, newValue)
-    }
-
-    override suspend fun invokeInstanceMethod(context: Context, name: String, args: Arguments): Obj {
-        if( name in publicFields ) return instanceContext[name]!!.value.invoke(context, this, args)
-        return super.invokeInstanceMethod(context, name, args)
-    }
-}

library/src/commonMain/kotlin/net/sergeych/lyng/ObjList.kt

@@ -1,137 +0,0 @@
-package net.sergeych.lyng
-
-class ObjList(val list: MutableList<Obj> = mutableListOf()) : Obj() {
-
-    init {
-        for (p in objClass.parents)
-            parentInstances.add(p.defaultInstance())
-    }
-
-    override fun toString(): String = "[${
-        list.joinToString(separator = ", ") { it.inspect() }
-    }]"
-
-    fun normalize(context: Context, index: Int, allowisEndInclusive: Boolean = false): Int {
-        val i = if (index < 0) list.size + index else index
-        if (allowisEndInclusive && i == list.size) return i
-        if (i !in list.indices) context.raiseError("index $index out of bounds for size ${list.size}")
-        return i
-    }
-
-    override suspend fun getAt(context: Context, index: Int): Obj {
-        val i = normalize(context, index)
-        return list[i]
-    }
-
-    override suspend fun putAt(context: Context, index: Int, newValue: Obj) {
-        val i = normalize(context, index)
-        list[i] = newValue
-    }
-
-    override suspend fun compareTo(context: Context, other: Obj): Int {
-        if (other !is ObjList) return -2
-        val mySize = list.size
-        val otherSize = other.list.size
-        val commonSize = minOf(mySize, otherSize)
-        for (i in 0..<commonSize) {
-            if (list[i].compareTo(context, other.list[i]) != 0) {
-                return list[i].compareTo(context, other.list[i])
-            }
-        }
-        // equal so far, longer is greater:
-        return when {
-            mySize < otherSize -> -1
-            mySize > otherSize -> 1
-            else -> 0
-        }
-    }
-
-    override suspend fun plus(context: Context, other: Obj): Obj =
-        when {
-            other is ObjList ->
-                ObjList((list + other.list).toMutableList())
-
-            other.isInstanceOf(ObjIterable) -> {
-                val l = other.callMethod<ObjList>(context, "toList")
-                ObjList((list + l.list).toMutableList())
-            }
-
-            else ->
-                context.raiseError("'+': can't concatenate $this with $other")
-        }
-
-
-    override suspend fun plusAssign(context: Context, other: Obj): Obj {
-        // optimization
-        if (other is ObjList) {
-            list += other.list
-            return this
-        }
-        if (other.isInstanceOf(ObjIterable)) {
-            val otherList = other.invokeInstanceMethod(context, "toList") as ObjList
-            list += otherList.list
-        } else
-            list += other
-        return this
-    }
-
-    override val objClass: ObjClass
-        get() = type
-
-    companion object {
-        val type = ObjClass("List", ObjArray).apply {
-
-            createField("size",
-                statement {
-                    (thisObj as ObjList).list.size.toObj()
-                }
-            )
-            addFn("getAt") {
-                requireExactCount(1)
-                thisAs<ObjList>().getAt(this, requiredArg<ObjInt>(0).value.toInt())
-            }
-            addFn("putAt") {
-                requireExactCount(2)
-                val newValue = args[1]
-                thisAs<ObjList>().putAt(this, requiredArg<ObjInt>(0).value.toInt(), newValue)
-                newValue
-            }
-            createField("add",
-                statement {
-                    val l = thisAs<ObjList>().list
-                    for (a in args) l.add(a)
-                    ObjVoid
-                }
-            )
-            createField("addAt",
-                statement {
-                    if (args.size < 2) raiseError("addAt takes 2+ arguments")
-                    val l = thisAs<ObjList>()
-                    var index = l.normalize(
-                        this, requiredArg<ObjInt>(0).value.toInt(),
-                        allowisEndInclusive = true
-                    )
-                    for (i in 1..<args.size) l.list.add(index++, args[i])
-                    ObjVoid
-                }
-            )
-            addFn("removeAt") {
-                val self = thisAs<ObjList>()
-                val start = self.normalize(this, requiredArg<ObjInt>(0).value.toInt())
-                if (args.size == 2) {
-                    val end = requireOnlyArg<ObjInt>().value.toInt()
-                    self.list.subList(start, self.normalize(this, end)).clear()
-                } else
-                    self.list.removeAt(start)
-                self
-            }
-            addFn("removeRangeInclusive") {
-                val self = thisAs<ObjList>()
-                val start = self.normalize(this, requiredArg<ObjInt>(0).value.toInt())
-                val end = self.normalize(this, requiredArg<ObjInt>(1).value.toInt()) + 1
-                self.list.subList(start, end).clear()
-                self
-            }
-        }
-    }
-}

library/src/commonMain/kotlin/net/sergeych/lyng/ObjString.kt

@@ -1,46 +0,0 @@
-package net.sergeych.lyng
-
-import kotlinx.serialization.SerialName
-import kotlinx.serialization.Serializable
-
-@Serializable
-@SerialName("string")
-data class ObjString(val value: String) : Obj() {
-
-    override suspend fun compareTo(context: Context, other: Obj): Int {
-        if (other !is ObjString) return -2
-        return this.value.compareTo(other.value)
-    }
-
-    override fun toString(): String = value
-
-    override val asStr: ObjString by lazy { this }
-
-    override fun inspect(): String {
-        return "\"$value\""
-    }
-
-    override val objClass: ObjClass
-        get() = type
-
-    override suspend fun plus(context: Context, other: Obj): Obj {
-        return ObjString(value + other.asStr.value)
-    }
-
-    override suspend fun getAt(context: Context, index: Int): Obj {
-        return ObjChar(value[index])
-    }
-
-    companion object {
-        val type = ObjClass("String").apply {
-            addConst("startsWith",
-                statement {
-                    ObjBool(thisAs<ObjString>().value.startsWith(requiredArg<ObjString>(0).value))
-                })
-            addConst("length",
-                statement { ObjInt(thisAs<ObjString>().value.length.toLong()) }
-            )
-            addFn("size") { ObjInt(thisAs<ObjString>().value.length.toLong()) }
-        }
-    }
-}

library/src/commonMain/kotlin/net/sergeych/lyng/SymbolSpace.kt

@@ -1,13 +0,0 @@
-package net.sergeych.lyng
-
-
-
-class Symbols(
-    unitType: UnitType,
-    val name: String,
-    val x: TypeDecl
-) {
-    enum class UnitType {
-        Module, Function, Lambda
-    }
-}

library/src/commonMain/kotlin/net/sergeych/lyng/TypeDecl.kt

@@ -1,21 +0,0 @@
-package net.sergeych.lyng
-
-sealed class TypeDecl {
-    // ??
-    data class Fn(val argTypes: List<ArgsDeclaration.Item>, val retType: TypeDecl) : TypeDecl()
-    object Obj : TypeDecl()
-}
-
-/*
-To use in the compiler, we need symbol information when:
-
-- declaring a class: the only way to export its public/protected symbols is to know it in compiler time
-- importing a module: actually,  we cam try to do it in a more efficient way.
-
-Importing module:
-
-The moudule is efficiently a statement, that initializes it with all its symbols modifying some context.
-
-The thing is, we need only
-
- */

library/src/commonMain/kotlin/net/sergeych/lyng/globals.kt

@@ -1,5 +0,0 @@
-package net.sergeych.lyng
-
-import net.sergeych.lyng.buildconfig.BuildConfig
-
-val LyngVersion = BuildConfig.VERSION

lyng/build.gradle.kts

@@ -29,11 +29,11 @@ kotlin {
     sourceSets {
         val commonMain by getting {
             dependencies {
-                implementation(project(":library"))
+                implementation(kotlin("stdlib-common"))
+                implementation(project(":lynglib"))
                 implementation(libs.okio)
-
                 implementation(libs.clikt)
-
+                implementation(kotlin("stdlib-common"))
                 // optional support for rendering markdown in help messages
 //                implementation(libs.clikt.markdown)
             }
@@ -42,9 +42,15 @@ kotlin {
             dependencies {
                 implementation(kotlin("test-common"))
                 implementation(kotlin("test-annotations-common"))
+                implementation(libs.kotlinx.coroutines.core)
                 implementation(libs.okio.fakefilesystem)
             }
         }
+//        val nativeMain by getting {
+//            dependencies {
+//                implementation(kotlin("stdlib-common"))
+//            }
+//        }
         val linuxX64Main by getting {
 
         }

lyng/src/commonMain/kotlin/Common.kt

@@ -17,14 +17,31 @@ import okio.use
 
 expect fun exit(code: Int)
 
+expect class ShellCommandExecutor {
+    fun executeCommand(command: String): CommandResult
+
+    companion object {
+        fun create(): ShellCommandExecutor
+    }
+}
+
+data class CommandResult(
+    val exitCode: Int,
+    val output: String,
+    val error: String
+)
+
 val baseContext = Context().apply {
     addFn("exit") {
         exit(requireOnlyArg<ObjInt>().toInt())
         ObjVoid
     }
+//    ObjString.type.addFn("shell") {
+//
+//    }
 }
 
-class LyngCLI(val launcher: (suspend () -> Unit) -> Unit) : CliktCommand() {
+class Lyng(val launcher: (suspend () -> Unit) -> Unit) : CliktCommand() {
 
     override val printHelpOnEmptyArgs = true
 
@@ -90,11 +107,16 @@ class LyngCLI(val launcher: (suspend () -> Unit) -> Unit) : CliktCommand() {
 }
 
 suspend fun executeFile(fileName: String) {
-    val text = FileSystem.SYSTEM.source(fileName.toPath()).use { fileSource ->
+    var text = FileSystem.SYSTEM.source(fileName.toPath()).use { fileSource ->
         fileSource.buffer().use { bs ->
             bs.readUtf8()
         }
     }
+    if( text.startsWith("#!") ) {
+        // skip shebang
+        val pos = text.indexOf('\n')
+        text = text.substring(pos + 1)
+    }
     processErrors {
         Compiler().compile(Source(fileName, text)).execute(baseContext)
     }

lyng/src/jvmMain/kotlin/Shell.jvm.kt

@@ -0,0 +1,23 @@
+@file:Suppress("EXPECT_ACTUAL_CLASSIFIERS_ARE_IN_BETA_WARNING")
+
+package net.sergeych
+
+// Alternative implementation for native targets
+actual class ShellCommandExecutor() {
+    actual fun executeCommand(command: String): CommandResult {
+        val process = ProcessBuilder("/bin/sh", "-c", command).start()
+        val exitCode = process.waitFor()
+        val output = process.inputStream.bufferedReader().readText()
+        val error = process.errorStream.bufferedReader().readText()
+
+        return CommandResult(
+            exitCode = exitCode,
+            output = output.trim(),
+            error = error.trim()
+        )
+    }
+
+    actual companion object {
+        actual fun create(): ShellCommandExecutor = ShellCommandExecutor()
+    }
+}

lyng/src/jvmMain/kotlin/net/sergeych/lyng_cli/Main.kt

@@ -2,8 +2,8 @@ package net.sergeych.lyng_cli
 
 import com.github.ajalt.clikt.core.main
 import kotlinx.coroutines.runBlocking
-import net.sergeych.LyngCLI
+import net.sergeych.Lyng
 
 fun main(args: Array<String>) {
-    LyngCLI({ runBlocking { it() } }).main(args)
+    Lyng({ runBlocking { it() } }).main(args)
 }

lyng/src/linuxX64Main/kotlin/Main.kt

@@ -1,7 +1,7 @@
 import com.github.ajalt.clikt.core.main
 import kotlinx.coroutines.runBlocking
-import net.sergeych.LyngCLI
+import net.sergeych.Lyng
 
 fun main(args: Array<String>) {
-    LyngCLI( { runBlocking { it() } }).main(args)
+    Lyng( { runBlocking { it() } }).main(args)
 }

lyng/src/nativeMain/kotlin/Common.native.kt

@@ -1,7 +1,48 @@
+@file:OptIn(ExperimentalForeignApi::class, ExperimentalForeignApi::class, ExperimentalForeignApi::class)
+
 package net.sergeych
 
+import kotlinx.cinterop.*
+import platform.posix.fgets
+import platform.posix.pclose
+import platform.posix.popen
 import kotlin.system.exitProcess
 
+actual class ShellCommandExecutor() {
+    actual fun executeCommand(command: String): CommandResult {
+        val outputBuilder = StringBuilder()
+        val errorBuilder = StringBuilder()
+
+        val fp = popen(command, "r") ?: return CommandResult(
+            exitCode = -1,
+            output = "",
+            error = "Failed to execute command"
+        )
+
+        val buffer = ByteArray(4096)
+        while (true) {
+            val bytesRead = buffer.usePinned { pinned ->
+                fgets(pinned.addressOf(0), buffer.size.convert(), fp)
+            }
+            if (bytesRead == null) break
+            outputBuilder.append(bytesRead.toKString())
+        }
+
+        val status = pclose(fp)
+        val exitCode = if (status == 0) 0 else 1
+
+        return CommandResult(
+            exitCode = exitCode,
+            output = outputBuilder.toString().trim(),
+            error = errorBuilder.toString().trim()
+        )
+    }
+
+    actual companion object {
+        actual fun create(): ShellCommandExecutor = ShellCommandExecutor()
+    }
+}
+
 actual fun exit(code: Int) {
     exitProcess(code)
 }

lynglib/build.gradle.kts

@@ -1,17 +1,40 @@
-import com.vanniktech.maven.publish.SonatypeHost
+import com.codingfeline.buildkonfig.compiler.FieldSpec.Type.STRING
 import org.jetbrains.kotlin.gradle.ExperimentalKotlinGradlePluginApi
 import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
+group = "net.sergeych"
+version = "0.6.8-SNAPSHOT"
+
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+    dependencies {
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.4.0")
+        classpath("com.codingfeline.buildkonfig:buildkonfig-gradle-plugin:latest_version")
+    }
+}
+
 plugins {
     alias(libs.plugins.kotlinMultiplatform)
     alias(libs.plugins.androidLibrary)
-    alias(libs.plugins.vanniktech.mavenPublish)
+//    alias(libs.plugins.vanniktech.mavenPublish)
     kotlin("plugin.serialization") version "2.1.20"
+    id("com.codingfeline.buildkonfig") version "0.17.1"
+    `maven-publish`
 }
 
-group = "net.sergeych"
-version = "0.2.0-SNAPSHOT"
+buildkonfig {
+    packageName = "net.sergeych.lyng"
+    // objectName = "YourAwesomeConfig"
+    // exposeObjectWithName = "YourAwesomePublicConfig"
+
+    defaultConfigs {
+        buildConfigField(STRING, "bcprovider", "codingfeline")
+        buildConfigField(STRING, "version", version.toString())
+    }
+}
 
 kotlin {
     jvm()
@@ -39,6 +62,7 @@ kotlin {
     sourceSets {
         all {
             languageSettings.optIn("kotlinx.coroutines.ExperimentalCoroutinesApi")
+            languageSettings.optIn("kotlin.contracts.ExperimentalContracts")
             languageSettings.optIn("kotlin.ExperimentalUnsignedTypes")
             languageSettings.optIn("kotlin.coroutines.DelicateCoroutinesApi")
         }
@@ -77,73 +101,54 @@ dependencies {
     implementation(libs.firebase.crashlytics.buildtools)
 }
 
-mavenPublishing {
-    publishToMavenCentral(SonatypeHost.CENTRAL_PORTAL)
-
-    signAllPublications()
-
-    coordinates(group.toString(), "library", version.toString())
-
-    pom {
-        name = "Lyng language"
-        description = "Kotlin-bound scripting loanguage"
-        inceptionYear = "2025"
-//        url = "https://sergeych.net"
-        licenses {
-            license {
-                name = "XXX"
-                url = "YYY"
-                distribution = "ZZZ"
+publishing {
+    val mavenToken by lazy {
+        File("${System.getProperty("user.home")}/.gitea_token").readText()
+    }
+    repositories {
+        maven {
+            credentials(HttpHeaderCredentials::class) {
+                name = "Authorization"
+                value = mavenToken
             }
-        }
-        developers {
-            developer {
-                id = "XXX"
-                name = "YYY"
-                url = "ZZZ"
+            url = uri("https://gitea.sergeych.net/api/packages/SergeychWorks/maven")
+            authentication {
+                create("Authorization", HttpHeaderAuthentication::class)
             }
         }
-        scm {
-            url = "XXX"
-            connection = "YYY"
-            developerConnection = "ZZZ"
-        }
     }
 }
 
-val projectVersion  by project.extra(provider {
-    // Compute value lazily
-    (version as String)
-})
-
-val generateBuildConfig by tasks.registering {
-    // Declare outputs safely
-    val outputDir = layout.buildDirectory.dir("generated/buildConfig/commonMain/kotlin")
-    outputs.dir(outputDir)
-
-    val version = projectVersion.get()
-
-    // Inputs: Version is tracked as an input
-    inputs.property("version", version)
-
-    doLast {
-        val packageName = "net.sergeych.lyng.buildconfig"
-        val packagePath = packageName.replace('.', '/')
-        val buildConfigFile = outputDir.get().file("$packagePath/BuildConfig.kt").asFile
-
-        buildConfigFile.parentFile?.mkdirs()
-        buildConfigFile.writeText(
-            """
-            |package $packageName
-            |
-            |object BuildConfig {
-            |    const val VERSION = "$version"
-            |}
-            """.trimMargin()
-        )
-    }
-}
-
-tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
-    dependsOn(generateBuildConfig)
-}
+//mavenPublishing {
+//    publishToMavenCentral(SonatypeHost.CENTRAL_PORTAL)
+//
+//    signAllPublications()
+//
+//    coordinates(group.toString(), "library", version.toString())
+//
+//    pom {
+//        name = "Lyng language"
+//        description = "Kotlin-bound scripting loanguage"
+//        inceptionYear = "2025"
+////        url = "https://sergeych.net"
+//        licenses {
+//            license {
+//                name = "XXX"
+//                url = "YYY"
+//                distribution = "ZZZ"
+//            }
+//        }
+//        developers {
+//            developer {
+//                id = "XXX"
+//                name = "YYY"
+//                url = "ZZZ"
+//            }
+//        }
+//        scm {
+//            url = "XXX"
+//            connection = "YYY"
+//            developerConnection = "ZZZ"
+//        }
+//    }
+//}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/AccessType.kt

@@ -0,0 +1,8 @@
+package net.sergeych.lyng
+
+enum class AccessType(val isMutable: Boolean) {
+    Val(false), Var(true),
+
+    @Suppress("unused")
+    Initialization(false)
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/AppliedContext.kt

@@ -0,0 +1,17 @@
+package net.sergeych.lyng
+
+/**
+ * Special version of the [Context] used to `apply` new this object to
+ * _parent context property.
+ *
+ * @param _parent context to apply to
+ * @param args arguments for the new context
+ * @param appliedContext the new context to apply, it will have lower priority except for `this` which
+ *      will be reset by appliedContext's `this`.
+ */
+class AppliedContext(_parent: Context, args: Arguments, val appliedContext: Context)
+    : Context(_parent, args, appliedContext.pos, appliedContext.thisObj) {
+    override fun get(name: String): ObjRecord? =
+        if (name == "this") thisObj.asReadonly
+        else super.get(name) ?: appliedContext[name]
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ArgsDeclaration.kt

@@ -11,7 +11,8 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
         val start = params.indexOfFirst { it.defaultValue != null }
         if (start >= 0)
             for (j in start + 1 until params.size)
-                if (params[j].defaultValue == null) throw ScriptError(
+                // last non-default could be lambda:
+                if (params[j].defaultValue == null && j != params.size - 1) throw ScriptError(
                     params[j].pos,
                     "required argument can't follow default one"
                 )
@@ -22,22 +23,41 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
      */
     suspend fun assignToContext(
         context: Context,
-        fromArgs: Arguments = context.args,
-        defaultAccessType: Compiler.AccessType = Compiler.AccessType.Var
+        arguments: Arguments = context.args,
+        defaultAccessType: AccessType = AccessType.Var,
+        defaultVisibility: Visibility = Visibility.Public
     ) {
         fun assign(a: Item, value: Obj) {
-            context.addItem(a.name, (a.accessType ?: defaultAccessType).isMutable, value)
+            context.addItem(a.name, (a.accessType ?: defaultAccessType).isMutable, value,
+                a.visibility ?: defaultVisibility)
+        }
+
+        // will be used with last lambda arg fix
+        val callArgs: List<Obj>
+        val paramsSize: Int
+
+        if( arguments.tailBlockMode ) {
+            paramsSize = params.size - 1
+            assign(params.last(), arguments.list.last())
+            callArgs = arguments.list.dropLast(1)
+        } else {
+            paramsSize = params.size
+            callArgs = arguments.list
         }
 
         suspend fun processHead(index: Int): Int {
             var i = index
-            while (i != params.size) {
+            while (i != paramsSize) {
                 val a = params[i]
                 if (a.isEllipsis) break
                 val value = when {
-                    i < fromArgs.size -> fromArgs[i]
+                    i < callArgs.size -> callArgs[i]
                     a.defaultValue != null -> a.defaultValue.execute(context)
-                    else -> context.raiseArgumentError("too few arguments for the call")
+                    else -> {
+                        println("callArgs: ${callArgs.joinToString()}")
+                        println("tailBlockMode: ${arguments.tailBlockMode}")
+                        context.raiseIllegalArgument("too few arguments for the call")
+                    }
                 }
                 assign(a, value)
                 i++
@@ -46,18 +66,18 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
         }
 
         suspend fun processTail(index: Int): Int {
-            var i = params.size - 1
-            var j = fromArgs.size - 1
+            var i = paramsSize - 1
+            var j = callArgs.size - 1
             while (i > index) {
                 val a = params[i]
                 if (a.isEllipsis) break
                 val value = when {
                     j >= index -> {
-                        fromArgs[j--]
+                        callArgs[j--]
                     }
 
                     a.defaultValue != null -> a.defaultValue.execute(context)
-                    else -> context.raiseArgumentError("too few arguments for the call")
+                    else -> context.raiseIllegalArgument("too few arguments for the call")
                 }
                 assign(a, value)
                 i--
@@ -68,17 +88,17 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
         fun processEllipsis(index: Int, toFromIndex: Int) {
             val a = params[index]
             val l = if (index > toFromIndex) ObjList()
-            else ObjList(fromArgs.values.subList(index, toFromIndex + 1).toMutableList())
+            else ObjList(callArgs.subList(index, toFromIndex + 1).toMutableList())
             assign(a, l)
         }
 
         val leftIndex = processHead(0)
-        if (leftIndex < params.size) {
+        if (leftIndex < paramsSize) {
             val end = processTail(leftIndex)
             processEllipsis(leftIndex, end)
         } else {
-            if (leftIndex < fromArgs.size)
-                context.raiseArgumentError("too many arguments for the call")
+            if (leftIndex < callArgs.size)
+                context.raiseIllegalArgument("too many arguments for the call")
         }
     }
 
@@ -90,7 +110,7 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
      */
     data class Item(
         val name: String,
-        val type: TypeDecl = TypeDecl.Obj,
+        val type: TypeDecl = TypeDecl.TypeAny,
         val pos: Pos = Pos.builtIn,
         val isEllipsis: Boolean = false,
         /**
@@ -98,7 +118,7 @@ data class ArgsDeclaration(val params: List<Item>, val endTokenType: Token.Type)
          * So it is a [Statement] that must be executed on __caller context__.
          */
         val defaultValue: Statement? = null,
-        val accessType: Compiler.AccessType? = null,
-        val visibility: Compiler.Visibility? = null,
+        val accessType: AccessType? = null,
+        val visibility: Visibility? = null,
     )
 }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Arguments.kt

@@ -0,0 +1,50 @@
+package net.sergeych.lyng
+
+data class ParsedArgument(val value: Statement, val pos: Pos, val isSplat: Boolean = false)
+
+suspend fun Collection<ParsedArgument>.toArguments(context: Context,tailBlockMode: Boolean): Arguments {
+    val list = mutableListOf<Obj>()
+
+    for (x in this) {
+        val value = x.value.execute(context)
+        if (x.isSplat) {
+            when {
+                value is ObjList -> {
+                    for (subitem in value.list) list.add(subitem)
+                }
+
+                value.isInstanceOf(ObjIterable) -> {
+                    val i = (value.invokeInstanceMethod(context, "toList") as ObjList).list
+                    i.forEach { list.add(it) }
+                }
+
+                else -> context.raiseClassCastError("expected list of objects for splat argument")
+            }
+        } else
+            list.add(value)
+    }
+    return Arguments(list,tailBlockMode)
+}
+
+data class Arguments(val list: List<Obj>,val tailBlockMode: Boolean = false) : List<Obj> by list {
+
+    constructor(vararg values: Obj) : this(values.toList())
+
+    fun firstAndOnly(pos: Pos = Pos.UNKNOWN): Obj {
+        if (list.size != 1) throw ScriptError(pos, "expected one argument, got ${list.size}")
+        return list.first()
+    }
+
+    /**
+     * Convert to list of kotlin objects, see [Obj.toKotlin].
+     */
+    suspend fun toKotlinList(context: Context): List<Any?> {
+        return list.map { it.toKotlin(context) }
+    }
+
+    companion object {
+        val EMPTY = Arguments(emptyList())
+        fun from(values: Collection<Obj>) = Arguments(values.toList())
+    }
+}
+

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt

@@ -11,18 +11,20 @@ class Compiler(
     class Settings
 
     fun compile(source: Source): Script {
-        return parseScript(source.startPos,
+        return parseScript(
+            source.startPos,
             CompilerContext(parseLyng(source))
         )
     }
 
     private fun parseScript(start: Pos, cc: CompilerContext): Script {
         val statements = mutableListOf<Statement>()
+//        val returnScope = cc.startReturnScope()
         while (parseStatement(cc, braceMeansLambda = true)?.also {
                 statements += it
             } != null) {/**/
         }
-        return Script(start, statements)
+        return Script(start, statements)//returnScope.needCatch)
     }
 
     private fun parseStatement(cc: CompilerContext, braceMeansLambda: Boolean = false): Statement? {
@@ -57,7 +59,7 @@ class Compiler(
                         parseBlock(cc)
                 }
 
-                Token.Type.RBRACE -> {
+                Token.Type.RBRACE, Token.Type.RBRACKET -> {
                     cc.previous()
                     return null
                 }
@@ -119,49 +121,91 @@ class Compiler(
                     operand = Accessor { op.getter(it).value.logicalNot(it).asReadonly }
                 }
 
-                Token.Type.DOT -> {
+                Token.Type.DOT, Token.Type.NULL_COALESCE -> {
+                    val isOptional = t.type == Token.Type.NULL_COALESCE
                     operand?.let { left ->
                         // dotcall: calling method on the operand, if next is ID, "("
                         var isCall = false
                         val next = cc.next()
                         if (next.type == Token.Type.ID) {
-                            cc.ifNextIs(Token.Type.LPAREN) {
-                                // instance method call
-                                val args = parseArgs(cc)
-                                isCall = true
-                                operand = Accessor { context ->
-                                    context.pos = next.pos
-                                    val v = left.getter(context).value
-                                    ObjRecord(
-                                        v.invokeInstanceMethod(
-                                            context,
-                                            next.value,
-                                            args.toArguments(context)
-                                        ), isMutable = false
-                                    )
+                            // could be () call or obj.method {} call
+                            val nt = cc.current()
+                            when (nt.type) {
+                                Token.Type.LPAREN -> {
+                                    cc.next()
+                                    // instance method call
+                                    val args = parseArgs(cc).first
+                                    isCall = true
+                                    operand = Accessor { context ->
+                                        context.pos = next.pos
+                                        val v = left.getter(context).value
+                                        if (v == ObjNull && isOptional)
+                                            ObjNull.asReadonly
+                                        else
+                                            ObjRecord(
+                                                v.invokeInstanceMethod(
+                                                    context,
+                                                    next.value,
+                                                    args.toArguments(context, false)
+                                                ), isMutable = false
+                                            )
+                                    }
                                 }
+
+
+                                Token.Type.LBRACE, Token.Type.NULL_COALESCE_BLOCKINVOKE -> {
+//                                    isOptional = nt.type == Token.Type.NULL_COALESCE_BLOCKINVOKE
+                                    // single lambda arg, like assertTrows { ... }
+                                    cc.next()
+                                    isCall = true
+                                    val lambda =
+                                        parseLambdaExpression(cc)
+                                    println(cc.current())
+                                    operand = Accessor { context ->
+                                        context.pos = next.pos
+                                        val v = left.getter(context).value
+                                        if (v == ObjNull && isOptional)
+                                            ObjNull.asReadonly
+                                        else
+                                            ObjRecord(
+                                                v.invokeInstanceMethod(
+                                                    context,
+                                                    next.value,
+                                                    Arguments(listOf(lambda.getter(context).value), true)
+                                                ), isMutable = false
+                                            )
+                                    }
+                                }
+
+                                else -> {}
                             }
                         }
                         if (!isCall) {
                             operand = Accessor({ context ->
-                                left.getter(context).value.readField(context, next.value)
+                                val x = left.getter(context).value
+                                if (x == ObjNull && isOptional) ObjNull.asReadonly
+                                else x.readField(context, next.value)
                             }) { cc, newValue ->
                                 left.getter(cc).value.writeField(cc, next.value, newValue)
                             }
                         }
-                    } ?: throw ScriptError(t.pos, "Expecting expression before dot")
+                    }
+
+                        ?: throw ScriptError(t.pos, "Expecting expression before dot")
                 }
 
                 Token.Type.COLONCOLON -> {
                     operand = parseScopeOperator(operand, cc)
                 }
 
-                Token.Type.LPAREN -> {
+                Token.Type.LPAREN, Token.Type.NULL_COALESCE_INVOKE -> {
                     operand?.let { left ->
                         // this is function call from <left>
                         operand = parseFunctionCall(
                             cc,
                             left,
+                            false,
+                            t.type == Token.Type.NULL_COALESCE_INVOKE
                         )
                     } ?: run {
                         // Expression in parentheses
@@ -174,15 +218,17 @@ class Compiler(
                     }
                 }
 
-                Token.Type.LBRACKET -> {
+                Token.Type.LBRACKET, Token.Type.NULL_COALESCE_INDEX -> {
                     operand?.let { left ->
                         // array access
+                        val isOptional = t.type == Token.Type.NULL_COALESCE_INDEX
                         val index = parseStatement(cc) ?: throw ScriptError(t.pos, "Expecting index expression")
                         cc.skipTokenOfType(Token.Type.RBRACKET, "missing ']' at the end of the list literal")
                         operand = Accessor({ cxt ->
-                            val i = (index.execute(cxt) as? ObjInt)?.value?.toInt()
-                                ?: cxt.raiseError("index must be integer")
-                            left.getter(cxt).value.getAt(cxt, i).asMutable
+                            val i = index.execute(cxt)
+                            val x = left.getter(cxt).value
+                            if (x == ObjNull && isOptional) ObjNull.asReadonly
+                            else x.getAt(cxt, i).asMutable
                         }) { cxt, newValue ->
                             val i = (index.execute(cxt) as? ObjInt)?.value?.toInt()
                                 ?: cxt.raiseError("index must be integer")
@@ -293,10 +339,10 @@ class Compiler(
                 }
 
                 Token.Type.DOTDOT, Token.Type.DOTDOTLT -> {
-                    // closed-range operator
+                    // range operator
                     val isEndInclusive = t.type == Token.Type.DOTDOT
                     val left = operand
-                    val right = parseStatement(cc)
+                    val right = parseExpression(cc)
                     operand = Accessor {
                         ObjRange(
                             left?.getter?.invoke(it)?.value ?: ObjNull,
@@ -306,17 +352,27 @@ class Compiler(
                     }
                 }
 
-                Token.Type.LBRACE -> {
-                    if (operand != null) {
-                        throw ScriptError(t.pos, "syntax error: lambda expression not allowed here")
-                    } else operand = parseLambdaExpression(cc)
+                Token.Type.LBRACE, Token.Type.NULL_COALESCE_BLOCKINVOKE -> {
+                    operand = operand?.let { left ->
+                        cc.previous()
+                        parseFunctionCall(
+                            cc,
+                            left,
+                            blockArgument = true,
+                            t.type == Token.Type.NULL_COALESCE_BLOCKINVOKE
+                        )
+                    } ?: parseLambdaExpression(cc)
                 }
 
+                Token.Type.RBRACKET, Token.Type.RPAREN -> {
+                    cc.previous()
+                    return operand
+                }
 
                 else -> {
                     cc.previous()
                     operand?.let { return it }
-                    operand = parseAccessor(cc) ?: throw ScriptError(t.pos, "Expecting expression")
+                    operand = parseAccessor(cc) ?: return null //throw ScriptError(t.pos, "Expecting expression")
                 }
             }
         }
@@ -331,16 +387,17 @@ class Compiler(
         val argsDeclaration = parseArgsDeclaration(cc)
         if (argsDeclaration != null && argsDeclaration.endTokenType != Token.Type.ARROW)
             throw ScriptError(startPos, "lambda must have either valid arguments declaration with '->' or no arguments")
-        val pos = cc.currentPos()
+
         val body = parseBlock(cc, skipLeadingBrace = true)
 
         var closure: Context? = null
 
         val callStatement = statement {
-            val context = closure!!.copy(pos, args)
+            // and the source closure of the lambda which might have other thisObj.
+            val context = AppliedContext(closure!!, args, this)
             if (argsDeclaration == null) {
                 // no args: automatic var 'it'
-                val l = args.values
+                val l = args.list
                 val itValue: Obj = when (l.size) {
                     // no args: it == void
                     0 -> ObjVoid
@@ -401,16 +458,6 @@ class Compiler(
         }
     }
 
-    enum class AccessType(val isMutable: Boolean) {
-        Val(false), Var(true),
-        @Suppress("unused")
-        Initialization(false)
-    }
-
-    enum class Visibility {
-        Public, Private, Protected, Internal
-    }
-
     /**
      * Parse argument declaration, used in lambda (and later in fn too)
      * @return declaration or null if there is no valid list of arguments
@@ -429,43 +476,14 @@ class Compiler(
                 }
 
                 Token.Type.NEWLINE -> {}
+
                 Token.Type.ID -> {
                     // visibility
-                    val visibility = when (t.value) {
-                        "private" -> {
-                            if (!isClassDeclaration) {
-                                cc.restorePos(startPos); return null
-                            }
-                            t = cc.next()
-                            Visibility.Private
-                        }
+                    val visibility = if (isClassDeclaration && t.value == "private") {
+                        t = cc.next()
+                        Visibility.Private
+                    } else Visibility.Public
 
-                        "protected" -> {
-                            if (!isClassDeclaration) {
-                                cc.restorePos(startPos); return null
-                            }
-                            t = cc.next()
-                            Visibility.Protected
-                        }
-
-                        "internal" -> {
-                            if (!isClassDeclaration) {
-                                cc.restorePos(startPos); return null
-                            }
-                            t = cc.next()
-                            Visibility.Internal
-                        }
-
-                        "public" -> {
-                            if (!isClassDeclaration) {
-                                cc.restorePos(startPos); return null
-                            }
-                            t = cc.next()
-                            Visibility.Public
-                        }
-
-                        else -> null
-                    }
                     // val/var?
                     val access = when (t.value) {
                         "val" -> {
@@ -542,14 +560,19 @@ class Compiler(
     }
 
     private fun parseTypeDeclaration(cc: CompilerContext): TypeDecl {
-        val result = TypeDecl.Obj
-        cc.ifNextIs(Token.Type.COLON) {
-            TODO("parse type declaration here")
-        }
-        return result
+        return if (cc.skipTokenOfType(Token.Type.COLON, isOptional = true)) {
+            val tt = cc.requireToken(Token.Type.ID, "type name or type expression required")
+            val isNullable = cc.skipTokenOfType(Token.Type.QUESTION, isOptional = true)
+            TypeDecl.Simple(tt.value, isNullable)
+        } else TypeDecl.TypeAny
     }
 
-    private fun parseArgs(cc: CompilerContext): List<ParsedArgument> {
+    /**
+     * Parse arguments list during the call and detect last block argument
+     * _following the parenthesis_ call: `(1,2) { ... }`
+     */
+    private fun parseArgs(cc: CompilerContext): Pair<List<ParsedArgument>, Boolean> {
+
         val args = mutableListOf<ParsedArgument>()
         do {
             val t = cc.next()
@@ -567,6 +590,8 @@ class Compiler(
                     cc.previous()
                     parseExpression(cc)?.let { args += ParsedArgument(it, t.pos) }
                         ?: throw ScriptError(t.pos, "Expecting arguments list")
+                    if (cc.current().type == Token.Type.COLON)
+                        parseTypeDeclaration(cc)
                     // Here should be a valid termination:
                 }
             }
@@ -574,6 +599,7 @@ class Compiler(
         // block after?
         val pos = cc.savePos()
         val end = cc.next()
+        var lastBlockArgument = false
         if (end.type == Token.Type.LBRACE) {
             // last argument - callable
             val callableAccessor = parseLambdaExpression(cc)
@@ -584,22 +610,40 @@ class Compiler(
                 },
                 end.pos
             )
+            lastBlockArgument = true
         } else
             cc.restorePos(pos)
-        return args
+        return args to lastBlockArgument
     }
 
 
-    private fun parseFunctionCall(cc: CompilerContext, left: Accessor): Accessor {
+    private fun parseFunctionCall(
+        cc: CompilerContext,
+        left: Accessor,
+        blockArgument: Boolean,
+        isOptional: Boolean
+    ): Accessor {
         // insofar, functions always return lvalue
-        val args = parseArgs(cc)
+        var detectedBlockArgument = blockArgument
+        val args = if (blockArgument) {
+            val blockArg = ParsedArgument(
+                parseExpression(cc)
+                    ?: throw ScriptError(cc.currentPos(), "lambda body expected"), cc.currentPos()
+            )
+            listOf(blockArg)
+        } else {
+            val r = parseArgs(cc)
+            detectedBlockArgument = r.second
+            r.first
+        }
 
         return Accessor { context ->
             val v = left.getter(context)
+            if (v.value == ObjNull && isOptional) return@Accessor v.value.asReadonly
             v.value.callOn(
                 context.copy(
                     context.pos,
-                    args.toArguments(context)
+                    args.toArguments(context, detectedBlockArgument)
 //                Arguments(
 //                    args.map { Arguments.Info((it.value as Statement).execute(context), it.pos) }
 //                ),
@@ -639,7 +683,7 @@ class Compiler(
                     "void" -> Accessor { ObjVoid.asReadonly }
                     "null" -> Accessor { ObjNull.asReadonly }
                     "true" -> Accessor { ObjBool(true).asReadonly }
-                    "false" -> Accessor { ObjBool(false).asReadonly }
+                    "false" -> Accessor { ObjFalse.asReadonly }
                     else -> {
                         Accessor({
                             it.pos = t.pos
@@ -682,28 +726,281 @@ class Compiler(
     }
 
     /**
-     * Parse keyword-starting statenment.
+     * Parse keyword-starting statement.
      * @return parsed statement or null if, for example. [id] is not among keywords
      */
     private fun parseKeywordStatement(id: Token, cc: CompilerContext): Statement? = when (id.value) {
-        "val" -> parseVarDeclaration(id.value, false, cc)
-        "var" -> parseVarDeclaration(id.value, true, cc)
+        "val" -> parseVarDeclaration(false, Visibility.Public, cc)
+        "var" -> parseVarDeclaration(true, Visibility.Public, cc)
         "while" -> parseWhileStatement(cc)
+        "do" -> parseDoWhileStatement(cc)
         "for" -> parseForStatement(cc)
         "break" -> parseBreakStatement(id.pos, cc)
         "continue" -> parseContinueStatement(id.pos, cc)
-        "fn", "fun" -> parseFunctionDeclaration(cc)
         "if" -> parseIfStatement(cc)
         "class" -> parseClassDeclaration(cc, false)
-        "struct" -> parseClassDeclaration(cc, true)
-        else -> null
+        "try" -> parseTryStatement(cc)
+        "throw" -> parseThrowStatement(cc)
+        "when" -> parseWhenStatement(cc)
+        else -> {
+            // triples
+            cc.previous()
+            val isExtern = cc.skipId("extern")
+            when {
+                cc.matchQualifiers("fun", "private") -> parseFunctionDeclaration(cc, Visibility.Private, isExtern)
+                cc.matchQualifiers("fn", "private") -> parseFunctionDeclaration(cc, Visibility.Private, isExtern)
+                cc.matchQualifiers("fun", "open") -> parseFunctionDeclaration(cc, isOpen = true, isExtern = isExtern)
+                cc.matchQualifiers("fn", "open") -> parseFunctionDeclaration(cc, isOpen = true, isExtern = isExtern)
+
+                cc.matchQualifiers("fun") -> parseFunctionDeclaration(cc, isOpen = false, isExtern = isExtern)
+                cc.matchQualifiers("fn") -> parseFunctionDeclaration(cc, isOpen = false, isExtern = isExtern)
+
+                cc.matchQualifiers("val", "private") -> parseVarDeclaration(false, Visibility.Private, cc)
+                cc.matchQualifiers("var", "private") -> parseVarDeclaration(true, Visibility.Private, cc)
+                cc.matchQualifiers("val", "open") -> parseVarDeclaration(false, Visibility.Private, cc, true)
+                cc.matchQualifiers("var", "open") -> parseVarDeclaration(true, Visibility.Private, cc, true)
+                else -> {
+                    cc.next()
+                    null
+                }
+            }
+        }
+    }
+
+    data class WhenCase(val condition: Statement, val block: Statement)
+
+    private fun parseWhenStatement(cc: CompilerContext): Statement {
+        // has a value, when(value) ?
+        var t = cc.skipWsTokens()
+        return if (t.type == Token.Type.LPAREN) {
+            // when(value)
+            val value = parseStatement(cc) ?: throw ScriptError(cc.currentPos(), "when(value) expected")
+            cc.skipTokenOfType(Token.Type.RPAREN)
+            t = cc.next()
+            if (t.type != Token.Type.LBRACE) throw ScriptError(t.pos, "when { ... } expected")
+            val cases = mutableListOf<WhenCase>()
+            var elseCase: Statement? = null
+            lateinit var whenValue: Obj
+
+            // there could be 0+ then clauses
+            // condition could be a value, in and is clauses:
+            // parse several conditions for one then clause
+
+            // loop cases
+            outer@ while (true) {
+
+                var skipParseBody = false
+                val currentCondition = mutableListOf<Statement>()
+
+                // loop conditions
+                while (true) {
+                    t = cc.skipWsTokens()
+
+                    when (t.type) {
+                        Token.Type.IN,
+                        Token.Type.NOTIN -> {
+                            // we need a copy in the closure:
+                            val isIn = t.type == Token.Type.IN
+                            val container = parseExpression(cc) ?: throw ScriptError(cc.currentPos(), "type expected")
+                            currentCondition += statement {
+                                val r = container.execute(this).contains(this, whenValue)
+                                ObjBool(if (isIn) r else !r)
+                            }
+                        }
+
+                        Token.Type.IS, Token.Type.NOTIS -> {
+                            // we need a copy in the closure:
+                            val isIn = t.type == Token.Type.IS
+                            val caseType = parseExpression(cc) ?: throw ScriptError(cc.currentPos(), "type expected")
+                            currentCondition += statement {
+                                val r = whenValue.isInstanceOf(caseType.execute(this))
+                                ObjBool(if (isIn) r else !r)
+                            }
+                        }
+
+                        Token.Type.COMMA ->
+                            continue
+
+                        Token.Type.ARROW ->
+                            break
+
+                        Token.Type.RBRACE ->
+                            break@outer
+
+                        else -> {
+                            if (t.value == "else") {
+                                cc.skipTokens(Token.Type.ARROW)
+                                if (elseCase != null) throw ScriptError(
+                                    cc.currentPos(),
+                                    "when else block already defined"
+                                )
+                                elseCase =
+                                    parseStatement(cc) ?: throw ScriptError(cc.currentPos(), "when else block expected")
+                                skipParseBody = true
+                            } else {
+                                cc.previous()
+                                val x = parseExpression(cc)
+                                    ?: throw ScriptError(cc.currentPos(), "when case condition expected")
+                                currentCondition += statement {
+                                    ObjBool(x.execute(this).compareTo(this, whenValue) == 0)
+                                }
+                            }
+                        }
+                    }
+                }
+                // parsed conditions?
+                if (!skipParseBody) {
+                    val block = parseStatement(cc) ?: throw ScriptError(cc.currentPos(), "when case block expected")
+                    for (c in currentCondition) cases += WhenCase(c, block)
+                }
+            }
+            statement {
+                var result: Obj = ObjVoid
+                // in / is and like uses whenValue from closure:
+                whenValue = value.execute(this)
+                var found = false
+                for (c in cases)
+                    if (c.condition.execute(this).toBool()) {
+                        result = c.block.execute(this)
+                        found = true
+                        break
+                    }
+                if (!found && elseCase != null) result = elseCase.execute(this)
+                result
+            }
+        } else {
+            // when { cond -> ... }
+            TODO("when without object is not yet implemented")
+        }
+    }
+
+    private fun parseThrowStatement(cc: CompilerContext): Statement {
+        val throwStatement = parseStatement(cc) ?: throw ScriptError(cc.currentPos(), "throw object expected")
+        return statement {
+            var errorObject = throwStatement.execute(this)
+            if (errorObject is ObjString)
+                errorObject = ObjException(this, errorObject.value)
+            if (errorObject is ObjException)
+                raiseError(errorObject)
+            else raiseError("this is not an exception object: $errorObject")
+        }
+    }
+
+    private data class CatchBlockData(
+        val catchVar: Token,
+        val classNames: List<String>,
+        val block: Statement
+    )
+
+    private fun parseTryStatement(cc: CompilerContext): Statement {
+        val body = parseBlock(cc)
+        val catches = mutableListOf<CatchBlockData>()
+        cc.skipTokens(Token.Type.NEWLINE)
+        var t = cc.next()
+        while (t.value == "catch") {
+
+            if (cc.skipTokenOfType(Token.Type.LPAREN, isOptional = true)) {
+                t = cc.next()
+                if (t.type != Token.Type.ID) throw ScriptError(t.pos, "expected catch variable")
+                val catchVar = t
+
+                val exClassNames = mutableListOf<String>()
+                if (cc.skipTokenOfType(Token.Type.COLON, isOptional = true)) {
+                    // load list of exception classes
+                    do {
+                        t = cc.next()
+                        if (t.type != Token.Type.ID)
+                            throw ScriptError(t.pos, "expected exception class name")
+                        exClassNames += t.value
+                        t = cc.next()
+                        when (t.type) {
+                            Token.Type.COMMA -> {
+                                continue
+                            }
+
+                            Token.Type.RPAREN -> {
+                                break
+                            }
+
+                            else -> throw ScriptError(t.pos, "syntax error: expected ',' or ')'")
+                        }
+                    } while (true)
+                } else {
+                    // no type!
+                    exClassNames += "Exception"
+                    cc.skipTokenOfType(Token.Type.RPAREN)
+                }
+                val block = parseBlock(cc)
+                catches += CatchBlockData(catchVar, exClassNames, block)
+                cc.skipTokens(Token.Type.NEWLINE)
+                t = cc.next()
+            } else {
+                // no (e: Exception) block: should be shortest variant `catch { ... }`
+                cc.skipTokenOfType(Token.Type.LBRACE, "expected catch(...) or catch { ... } here")
+                catches += CatchBlockData(
+                    Token("it", cc.currentPos(), Token.Type.ID), listOf("Exception"),
+                    parseBlock(cc, true)
+                )
+                t = cc.next()
+            }
+        }
+        val finallyClause = if (t.value == "finally") {
+            parseBlock(cc)
+        } else {
+            cc.previous()
+            null
+        }
+
+        if (catches.isEmpty() && finallyClause == null)
+            throw ScriptError(cc.currentPos(), "try block must have either catch or finally clause or both")
+
+        return statement {
+            var result: Obj = ObjVoid
+            try {
+                // body is a parsed block, it already has separate context
+                result = body.execute(this)
+            } catch (e: Exception) {
+                // convert to appropriate exception
+                val objException = when (e) {
+                    is ExecutionError -> e.errorObject
+                    else -> ObjUnknownException(this, e.message ?: e.toString())
+                }
+                // let's see if we should catch it:
+                var isCaught = false
+                for (cdata in catches) {
+                    var exceptionObject: ObjException? = null
+                    for (exceptionClassName in cdata.classNames) {
+                        val exObj = ObjException.getErrorClass(exceptionClassName)
+                            ?: raiseSymbolNotFound("error clas not exists: $exceptionClassName")
+                        if (objException.isInstanceOf(exObj)) {
+                            exceptionObject = objException
+                            break
+                        }
+                    }
+                    if (exceptionObject != null) {
+                        val catchContext = this.copy(pos = cdata.catchVar.pos)
+                        catchContext.addItem(cdata.catchVar.value, false, objException)
+                        result = cdata.block.execute(catchContext)
+                        isCaught = true
+                        break
+                    }
+                }
+                // rethrow if not caught this exception
+                if (!isCaught)
+                    throw e
+            } finally {
+                // finally clause does not alter result!
+                finallyClause?.execute(this)
+            }
+            result
+        }
     }
 
     private fun parseClassDeclaration(cc: CompilerContext, isStruct: Boolean): Statement {
         val nameToken = cc.requireToken(Token.Type.ID)
         val constructorArgsDeclaration =
             if (cc.skipTokenOfType(Token.Type.LPAREN, isOptional = true))
-                parseArgsDeclaration(cc)
+                parseArgsDeclaration(cc, isClassDeclaration = true)
             else null
 
         if (constructorArgsDeclaration != null && constructorArgsDeclaration.endTokenType != Token.Type.RPAREN)
@@ -743,41 +1040,12 @@ class Compiler(
             // fields. Note that 'this' is already set by class
             constructorArgsDeclaration?.assignToContext(this)
             bodyInit?.execute(this)
-            // export public
-            for( (name,record) in objects ) {
-                println("-- $name $record")
-                when(record.visibility) {
-                    Visibility.Public -> {
-                        thisObj.publicFields += name
-                        thisObj.protectedFields += name
-                    }
-                    Visibility.Protected ->
-                        thisObj.protectedFields += name
-                    else -> {
-                    }
-                }
-            }
 
             thisObj
         }
         // inheritance must alter this code:
         val newClass = ObjClass(className).apply {
             instanceConstructor = constructorCode
-            constructorArgsDeclaration?.let { cad ->
-                // we need accessors for all fields:
-                for (f in cad.params) {
-                    createField(
-                        f.name,
-                        statement {
-                            val context = (thisObj as ObjInstance).instanceContext
-                            println("called on $thisObj")
-                            context[f.name]?.value ?: raiseError("field is not initialized: ${f.name}")
-                        },
-                        true,
-//                        (f.accessType ?: defaultAccess).isMutable,
-                    )
-                }
-            }
         }
 
         return statement {
@@ -856,7 +1124,7 @@ class Compiler(
                     var breakCaught = false
 
                     if (size > 0) {
-                        var current = runCatching { sourceObj.getAt(forContext, 0) }
+                        var current = runCatching { sourceObj.getAt(forContext, ObjInt(0)) }
                             .getOrElse {
                                 throw ScriptError(
                                     tOp.pos,
@@ -883,7 +1151,7 @@ class Compiler(
                                 }
                             } else result = body.execute(forContext)
                             if (++index >= size) break
-                            current = sourceObj.getAt(forContext, index)
+                            current = sourceObj.getAt(forContext, ObjInt(index.toLong()))
                         }
                     }
                     if (!breakCaught && elseStatement != null) {
@@ -913,8 +1181,9 @@ class Compiler(
                 } catch (lbe: LoopBreakContinueException) {
                     if (lbe.label == label || lbe.label == null) {
                         if (lbe.doContinue) continue
+                        return lbe.result
                     }
-                    return lbe.result
+                    throw lbe
                 }
             }
         } else {
@@ -941,8 +1210,9 @@ class Compiler(
                 } catch (lbe: LoopBreakContinueException) {
                     if (lbe.label == label || lbe.label == null) {
                         if (lbe.doContinue) continue
+                        return lbe.result
                     }
-                    return lbe.result
+                    throw lbe
                 }
             else {
                 loopVar.value = iterObj.invokeInstanceMethod(forContext, "next")
@@ -952,6 +1222,59 @@ class Compiler(
         return elseStatement?.execute(forContext) ?: result
     }
 
+    @Suppress("UNUSED_VARIABLE")
+    private fun parseDoWhileStatement(cc: CompilerContext): Statement {
+        val label = getLabel(cc)?.also { cc.labels += it }
+        val (breakFound, body) = cc.parseLoop {
+            parseStatement(cc) ?: throw ScriptError(cc.currentPos(), "Bad while statement: expected statement")
+        }
+        label?.also { cc.labels -= it }
+
+        cc.skipTokens(Token.Type.NEWLINE)
+
+        val t = cc.next()
+        if (t.type != Token.Type.ID && t.value != "while")
+            cc.skipTokenOfType(Token.Type.LPAREN, "expected '(' here")
+
+        val conditionStart = ensureLparen(cc)
+        val condition =
+            parseExpression(cc) ?: throw ScriptError(conditionStart, "Bad while statement: expected expression")
+        ensureRparen(cc)
+
+        cc.skipTokenOfType(Token.Type.NEWLINE, isOptional = true)
+        val elseStatement = if (cc.next().let { it.type == Token.Type.ID && it.value == "else" }) {
+            parseStatement(cc)
+        } else {
+            cc.previous()
+            null
+        }
+
+
+        return statement(body.pos) {
+            var wasBroken = false
+            var result: Obj = ObjVoid
+            lateinit var doContext: Context
+            do {
+                doContext = it.copy().apply { skipContextCreation = true }
+                try {
+                    result = body.execute(doContext)
+                } catch (e: LoopBreakContinueException) {
+                    if (e.label == label || e.label == null) {
+                        if (e.doContinue) continue
+                        else {
+                            result = e.result
+                            wasBroken = true
+                            break
+                        }
+                    }
+                    throw e
+                }
+            } while (condition.execute(doContext).toBool())
+            if (!wasBroken) elseStatement?.let { s -> result = s.execute(it) }
+            result
+        }
+    }
+
     private fun parseWhileStatement(cc: CompilerContext): Statement {
         val label = getLabel(cc)?.also { cc.labels += it }
         val start = ensureLparen(cc)
@@ -1101,26 +1424,36 @@ class Compiler(
         }
     }
 
-    private fun parseFunctionDeclaration(tokens: CompilerContext): Statement {
-        var t = tokens.next()
+    private fun parseFunctionDeclaration(
+        cc: CompilerContext,
+        visibility: Visibility = Visibility.Public,
+        @Suppress("UNUSED_PARAMETER") isOpen: Boolean = false,
+        isExtern: Boolean = false
+    ): Statement {
+        var t = cc.next()
         val start = t.pos
         val name = if (t.type != Token.Type.ID)
             throw ScriptError(t.pos, "Expected identifier after 'fn'")
         else t.value
 
-        t = tokens.next()
+        t = cc.next()
         if (t.type != Token.Type.LPAREN)
             throw ScriptError(t.pos, "Bad function definition: expected '(' after 'fn ${name}'")
 
-        val argsDeclaration = parseArgsDeclaration(tokens)
+        val argsDeclaration = parseArgsDeclaration(cc)
         if (argsDeclaration == null || argsDeclaration.endTokenType != Token.Type.RPAREN)
             throw ScriptError(
                 t.pos,
                 "Bad function definition: expected valid argument declaration or () after 'fn ${name}'"
             )
 
+        if (cc.current().type == Token.Type.COLON) parseTypeDeclaration(cc)
+
         // Here we should be at open body
-        val fnStatements = parseBlock(tokens)
+        val fnStatements = if (isExtern)
+            statement { raiseError("extern function not provided: $name") }
+        else
+            parseBlock(cc)
 
         var closure: Context? = null
 
@@ -1138,7 +1471,7 @@ class Compiler(
             // we added fn in the context. now we must save closure
             // for the function
             closure = context
-            context.addItem(name, false, fnBody)
+            context.addItem(name, false, fnBody, visibility)
             // as the function can be called from anywhere, we have
             // saved the proper context in the closure
             fnBody
@@ -1155,7 +1488,7 @@ class Compiler(
         val block = parseScript(startPos, cc)
         return statement(startPos) {
             // block run on inner context:
-            block.execute(it.copy(startPos))
+            block.execute(if (it.skipContextCreation) it else it.copy(startPos))
         }.also {
             val t1 = cc.next()
             if (t1.type != Token.Type.RBRACE)
@@ -1163,17 +1496,22 @@ class Compiler(
         }
     }
 
-    private fun parseVarDeclaration(kind: String, mutable: Boolean, tokens: CompilerContext): Statement {
+    private fun parseVarDeclaration(
+        isMutable: Boolean,
+        visibility: Visibility,
+        tokens: CompilerContext,
+        @Suppress("UNUSED_PARAMETER") isOpen: Boolean = false
+    ): Statement {
         val nameToken = tokens.next()
         val start = nameToken.pos
         if (nameToken.type != Token.Type.ID)
-            throw ScriptError(nameToken.pos, "Expected identifier after '$kind'")
+            throw ScriptError(nameToken.pos, "Expected identifier here")
         val name = nameToken.value
 
         val eqToken = tokens.next()
         var setNull = false
         if (eqToken.type != Token.Type.ASSIGN) {
-            if (!mutable)
+            if (!isMutable)
                 throw ScriptError(start, "val must be initialized")
             else {
                 tokens.previous()
@@ -1181,7 +1519,7 @@ class Compiler(
             }
         }
 
-        val initialExpression = if (setNull) null else parseExpression(tokens)
+        val initialExpression = if (setNull) null else parseStatement(tokens, true)
             ?: throw ScriptError(eqToken.pos, "Expected initializer expression")
 
         return statement(nameToken.pos) { context ->
@@ -1192,8 +1530,8 @@ class Compiler(
             // create a separate copy:
             val initValue = initialExpression?.execute(context)?.byValueCopy() ?: ObjNull
 
-            context.addItem(name, mutable, initValue)
-            ObjVoid
+            context.addItem(name, isMutable, initValue, visibility)
+            initValue
         }
     }
 
@@ -1291,6 +1629,8 @@ class Compiler(
             // bitwise or 2
             // bitwise and 3
             // equality/ne 4
+            Operator.simple(Token.Type.EQARROW, ++lastPrty) { c, a, b -> ObjMapEntry(a, b) },
+            //
             Operator.simple(Token.Type.EQ, ++lastPrty) { c, a, b -> ObjBool(a.compareTo(c, b) == 0) },
             Operator.simple(Token.Type.NEQ, lastPrty) { c, a, b -> ObjBool(a.compareTo(c, b) != 0) },
             Operator.simple(Token.Type.REF_EQ, lastPrty) { _, a, b -> ObjBool(a === b) },
@@ -1305,6 +1645,9 @@ class Compiler(
             Operator.simple(Token.Type.NOTIN, lastPrty) { c, a, b -> ObjBool(!b.contains(c, a)) },
             Operator.simple(Token.Type.IS, lastPrty) { c, a, b -> ObjBool(a.isInstanceOf(b)) },
             Operator.simple(Token.Type.NOTIS, lastPrty) { c, a, b -> ObjBool(!a.isInstanceOf(b)) },
+
+            Operator.simple(Token.Type.ELVIS, ++lastPrty) { c, a, b -> if (a == ObjNull) b else a },
+
             // shuttle <=> 6
             Operator.simple(Token.Type.SHUTTLE, ++lastPrty) { c, a, b ->
                 ObjInt(a.compareTo(c, b).toLong())
@@ -1336,7 +1679,8 @@ class Compiler(
         /**
          * The keywords that stop processing of expression term
          */
-        val stopKeywords = setOf("break", "continue", "return", "if", "when", "do", "while", "for", "class", "struct")
+        val stopKeywords =
+            setOf("do", "break", "continue", "return", "if", "when", "do", "while", "for", "class")
     }
 }
 

lynglib/src/commonMain/kotlin/net/sergeych/lyng/CompilerContext.kt

@@ -9,7 +9,7 @@ internal class CompilerContext(val tokens: List<Token>) {
     var loopLevel = 0
         private set
 
-    inline fun <T> parseLoop(f: () -> T): Pair<Boolean,T> {
+    inline fun <T> parseLoop(f: () -> T): Pair<Boolean, T> {
         if (++loopLevel == 0) breakFound = false
         val result = f()
         return Pair(breakFound, result).also {
@@ -21,7 +21,11 @@ internal class CompilerContext(val tokens: List<Token>) {
 
     fun hasNext() = currentIndex < tokens.size
     fun hasPrevious() = currentIndex > 0
-    fun next() = tokens.getOrElse(currentIndex) { throw IllegalStateException("No next token") }.also { currentIndex++ }
+    fun next() =
+        if( currentIndex < tokens.size ) tokens[currentIndex++]
+        else Token("", tokens.last().pos, Token.Type.EOF)
+//        throw IllegalStateException("No more tokens")
+
     fun previous() = if (!hasPrevious()) throw IllegalStateException("No previous token") else tokens[--currentIndex]
 
     fun savePos() = currentIndex
@@ -47,9 +51,21 @@ internal class CompilerContext(val tokens: List<Token>) {
         throw ScriptError(at, message)
     }
 
-    fun currentPos() =
-        if (hasNext()) next().pos.also { previous() }
-        else previous().pos.also { next() }
+    fun currentPos(): Pos = tokens[currentIndex].pos
+
+    /**
+     * If the next token is identifier `name`, skip it and return `true`.
+     * else leave where it is and return `false`
+     */
+    fun skipId(name: String): Boolean {
+        current().let { t ->
+            if( t.type == Token.Type.ID && t.value == name ) {
+                next()
+                return true
+            }
+        }
+        return false
+    }
 
     /**
      * Skips next token if its type is `tokenType`, returns `true` if so.
@@ -98,4 +114,63 @@ internal class CompilerContext(val tokens: List<Token>) {
         breakFound = true
     }
 
+    /**
+     * Return value of the next token if it is an identifier, null otherwise.
+     * Does not change position.
+     */
+    @Suppress("unused")
+    fun nextIdValue(): String? {
+        return if (hasNext()) {
+            val nt = tokens[currentIndex]
+            if (nt.type == Token.Type.ID)
+                nt.value
+            else null
+        } else null
+    }
+
+    @Suppress("unused")
+    fun current(): Token = tokens[currentIndex]
+
+    /**
+     * If the token at current position plus offset (could be negative) exists, returns it, otherwise returns null.
+     */
+    @Suppress("unused")
+    fun atOffset(offset: Int): Token? =
+        if (currentIndex + offset in tokens.indices) tokens[currentIndex + offset] else null
+
+    fun matchQualifiers(keyword: String, vararg qualifiers: String): Boolean {
+        val pos = savePos()
+        var count = 0
+        while( count < qualifiers.size) {
+            val t = next()
+            when(t.type) {
+                Token.Type.ID -> {
+                    if( t.value in qualifiers ) count++
+                    else { restorePos(pos); return false }
+                }
+                Token.Type.MULTILINE_COMMENT, Token.Type.SINLGE_LINE_COMMENT, Token.Type.NEWLINE -> {}
+                else -> { restorePos(pos); return false }
+            }
+        }
+        val t = next()
+        if( t.type == Token.Type.ID && t.value == keyword ) {
+            return true
+        } else {
+            restorePos(pos)
+            return false
+        }
+    }
+
+    /**
+     * Skip newlines and comments. Returns (and reads) first non-whitespace token.
+     * Note that [Token.Type.EOF] is not considered a whitespace token.
+     */
+    fun skipWsTokens(): Token {
+        while( current().type in wstokens ) next()
+        return next()
+    }
+
+    companion object {
+        val wstokens = setOf(Token.Type.NEWLINE, Token.Type.MULTILINE_COMMENT, Token.Type.SINLGE_LINE_COMMENT)
+    }
 }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Context.kt

@@ -1,10 +1,11 @@
 package net.sergeych.lyng
 
-class Context(
+open class Context(
     val parent: Context?,
     val args: Arguments = Arguments.EMPTY,
     var pos: Pos = Pos.builtIn,
-    val thisObj: Obj = ObjVoid
+    var thisObj: Obj = ObjVoid,
+    var skipContextCreation: Boolean = false,
 ) {
     constructor(
         args: Arguments = Arguments.EMPTY,
@@ -15,33 +16,38 @@ class Context(
     fun raiseNotImplemented(what: String = "operation"): Nothing = raiseError("$what is not implemented")
 
     @Suppress("unused")
-    fun raiseNPE(): Nothing = raiseError(ObjNullPointerError(this))
+    fun raiseNPE(): Nothing = raiseError(ObjNullReferenceException(this))
 
     @Suppress("unused")
     fun raiseIndexOutOfBounds(message: String = "Index out of bounds"): Nothing =
-        raiseError(ObjIndexOutOfBoundsError(this, message))
+        raiseError(ObjIndexOutOfBoundsException(this, message))
 
     @Suppress("unused")
-    fun raiseArgumentError(message: String = "Illegal argument error"): Nothing =
-        raiseError(ObjIllegalArgumentError(this, message))
-
-    fun raiseClassCastError(msg: String): Nothing = raiseError(ObjClassCastError(this, msg))
+    fun raiseIllegalArgument(message: String = "Illegal argument error"): Nothing =
+        raiseError(ObjIllegalArgumentException(this, message))
 
     @Suppress("unused")
-    fun raiseSymbolNotFound(name: String): Nothing = raiseError(ObjSymbolNotDefinedError(this, "symbol is not defined: $name"))
+    fun raiseNoSuchElement(message: String = "No such element"): Nothing =
+        raiseError(ObjIllegalArgumentException(this, message))
+
+    fun raiseClassCastError(msg: String): Nothing = raiseError(ObjClassCastException(this, msg))
+
+    @Suppress("unused")
+    fun raiseSymbolNotFound(name: String): Nothing =
+        raiseError(ObjSymbolNotDefinedException(this, "symbol is not defined: $name"))
 
     fun raiseError(message: String): Nothing {
-        throw ExecutionError(ObjError(this, message))
+        throw ExecutionError(ObjException(this, message))
     }
 
-    fun raiseError(obj: ObjError): Nothing {
+    fun raiseError(obj: ObjException): Nothing {
         throw ExecutionError(obj)
     }
 
     inline fun <reified T : Obj> requiredArg(index: Int): T {
         if (args.list.size <= index) raiseError("Expected at least ${index + 1} argument, got ${args.list.size}")
-        return (args.list[index].value as? T)
-            ?: raiseClassCastError("Expected type ${T::class.simpleName}, got ${args.list[index].value::class.simpleName}")
+        return (args.list[index] as? T)
+            ?: raiseClassCastError("Expected type ${T::class.simpleName}, got ${args.list[index]::class.simpleName}")
     }
 
     inline fun <reified T : Obj> requireOnlyArg(): T {
@@ -61,9 +67,12 @@ class Context(
 
     internal val objects = mutableMapOf<String, ObjRecord>()
 
-    operator fun get(name: String): ObjRecord? =
-        objects[name]
-            ?: parent?.get(name)
+    open operator fun get(name: String): ObjRecord? =
+        if (name == "this") thisObj.asReadonly
+        else {
+            objects[name]
+                ?: parent?.get(name)
+        }
 
     fun copy(pos: Pos, args: Arguments = Arguments.EMPTY, newThisObj: Obj? = null): Context =
         Context(this, args, pos, newThisObj ?: thisObj)
@@ -73,8 +82,13 @@ class Context(
 
     fun copy() = Context(this, args, pos, thisObj)
 
-    fun addItem(name: String, isMutable: Boolean, value: Obj): ObjRecord {
-        return ObjRecord(value, isMutable).also { objects.put(name, it) }
+    fun addItem(
+        name: String,
+        isMutable: Boolean,
+        value: Obj,
+        visibility: Visibility = Visibility.Public
+    ): ObjRecord {
+        return ObjRecord(value, isMutable, visibility).also { objects[name] = it }
     }
 
     fun getOrCreateNamespace(name: String): ObjClass {
@@ -112,5 +126,4 @@ class Context(
 
     fun containsLocal(name: String): Boolean = name in objects
 
-
 }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Obj.kt

@@ -4,7 +4,10 @@ import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
+import net.sergeych.bintools.encodeToHex
 import net.sergeych.synctools.ProtectedOp
+import net.sergeych.synctools.withLock
+import kotlin.contracts.ExperimentalContracts
 
 /**
  * Record to store object with access rules, e.g. [isMutable] and access level [visibility].
@@ -12,7 +15,7 @@ import net.sergeych.synctools.ProtectedOp
 data class ObjRecord(
     var value: Obj,
     val isMutable: Boolean,
-    val visibility: Compiler.Visibility = Compiler.Visibility.Public
+    val visibility: Visibility = Visibility.Public
 )
 
 /**
@@ -39,6 +42,9 @@ data class Accessor(
 }
 
 open class Obj {
+
+    val isNull by lazy { this === ObjNull }
+
     var isFrozen: Boolean = false
 
     private val monitor = Mutex()
@@ -58,12 +64,16 @@ open class Obj {
      */
     open fun byValueCopy(): Obj = this
 
-    fun isInstanceOf(someClass: Obj) = someClass === objClass || objClass.allParentsSet.contains(someClass)
+    @Suppress("SuspiciousEqualsCombination")
+    fun isInstanceOf(someClass: Obj) = someClass === objClass ||
+            objClass.allParentsSet.contains(someClass) ||
+            someClass == rootObjectType
+
 
     suspend fun invokeInstanceMethod(context: Context, name: String, vararg args: Obj): Obj =
-        invokeInstanceMethod(context, name, Arguments(args.map { Arguments.Info(it, context.pos) }))
+        invokeInstanceMethod(context, name, Arguments(args.toList()))
 
-    inline suspend fun <reified T : Obj> callMethod(
+    suspend inline fun <reified T : Obj> callMethod(
         context: Context,
         name: String,
         args: Arguments = Arguments.EMPTY
@@ -86,7 +96,7 @@ open class Obj {
     }
 
     open suspend fun contains(context: Context, other: Obj): Boolean {
-        context.raiseNotImplemented()
+        return invokeInstanceMethod(context, "contains", other).toBool()
     }
 
     open val asStr: ObjString by lazy {
@@ -97,16 +107,7 @@ open class Obj {
      * Class of the object: definition of member functions (top-level), etc.
      * Note that using lazy allows to avoid endless recursion here
      */
-    open val objClass: ObjClass by lazy {
-        ObjClass("Obj").apply {
-            addFn("toString") {
-                thisObj.asStr
-            }
-            addFn("contains") {
-                ObjBool(thisObj.contains(this, args.firstAndOnly()))
-            }
-        }
-    }
+    open val objClass: ObjClass = rootObjectType
 
     open suspend fun plus(context: Context, other: Obj): Obj {
         context.raiseNotImplemented()
@@ -173,17 +174,23 @@ open class Obj {
         context.raiseNotImplemented()
     }
 
+    /**
+     * Convert Lyng object to its Kotlin counterpart
+     */
+    open suspend fun toKotlin(context: Context): Any? {
+        return toString()
+    }
+
     fun willMutate(context: Context) {
         if (isFrozen) context.raiseError("attempt to mutate frozen object")
     }
 
     suspend fun <T> sync(block: () -> T): T = monitor.withLock { block() }
 
-    suspend open fun readField(context: Context, name: String): ObjRecord {
+    open suspend fun readField(context: Context, name: String): ObjRecord {
         // could be property or class field:
         val obj = objClass.getInstanceMemberOrNull(name) ?: context.raiseError("no such field: $name")
-        val value = obj.value
-        return when (value) {
+        return when (val value = obj.value) {
             is Statement -> {
                 ObjRecord(value.execute(context.copy(context.pos, newThisObj = this)), obj.isMutable)
             }
@@ -199,7 +206,7 @@ open class Obj {
         if (field.isMutable) field.value = newValue else context.raiseError("can't assign to read-only field: $name")
     }
 
-    open suspend fun getAt(context: Context, index: Int): Obj {
+    open suspend fun getAt(context: Context, index: Obj): Obj {
         context.raiseNotImplemented("indexing")
     }
 
@@ -218,7 +225,7 @@ open class Obj {
         callOn(
             context.copy(
                 context.pos,
-                args = Arguments(args.map { Arguments.Info(it, context.pos) }),
+                args = Arguments(args.toList()),
                 newThisObj = thisObj
             )
         )
@@ -241,7 +248,33 @@ open class Obj {
 
 
     companion object {
-        inline fun <reified T> from(obj: T): Obj {
+
+        val rootObjectType = ObjClass("Obj").apply {
+                addFn("toString") {
+                    thisObj.asStr
+                }
+                addFn("contains") {
+                    ObjBool(thisObj.contains(this, args.firstAndOnly()))
+                }
+                // utilities
+                addFn("let") {
+                    args.firstAndOnly().callOn(copy(Arguments(thisObj)))
+                }
+                addFn("apply") {
+                    val newContext = ( thisObj as? ObjInstance)?.instanceContext ?: this
+                    args.firstAndOnly()
+                        .callOn(newContext)
+                    thisObj
+                }
+                addFn("also") {
+                    args.firstAndOnly().callOn(copy(Arguments(thisObj)))
+                    thisObj
+                }
+            }
+
+
+        inline fun from(obj: Any?): Obj {
+            @Suppress("UNCHECKED_CAST")
             return when (obj) {
                 is Obj -> obj
                 is Double -> ObjReal(obj)
@@ -251,8 +284,15 @@ open class Obj {
                 is String -> ObjString(obj)
                 is CharSequence -> ObjString(obj.toString())
                 is Boolean -> ObjBool(obj)
+                is Set<*> -> ObjSet((obj as Set<Obj>).toMutableSet())
                 Unit -> ObjVoid
                 null -> ObjNull
+                is Iterator<*> -> ObjKotlinIterator(obj)
+                is Map.Entry<*, *> -> {
+                    obj as MutableMap.MutableEntry<Obj, Obj>
+                    ObjMapEntry(obj.key, obj.value)
+                }
+
                 else -> throw IllegalArgumentException("cannot convert to Obj: $obj")
             }
         }
@@ -286,6 +326,32 @@ object ObjNull : Obj() {
     override fun equals(other: Any?): Boolean {
         return other is ObjNull || other == null
     }
+
+    override suspend fun readField(context: Context, name: String): ObjRecord {
+        context.raiseNPE()
+    }
+
+    override suspend fun invokeInstanceMethod(context: Context, name: String, args: Arguments): Obj {
+        context.raiseNPE()
+    }
+
+    override suspend fun getAt(context: Context, index: Obj): Obj {
+        context.raiseNPE()
+    }
+
+    override suspend fun putAt(context: Context, index: Int, newValue: Obj) {
+        context.raiseNPE()
+    }
+
+    override suspend fun callOn(context: Context): Obj {
+        context.raiseNPE()
+    }
+
+    override fun toString(): String = "null"
+
+    override suspend fun toKotlin(context: Context): Any? {
+        return null
+    }
 }
 
 interface Numeric {
@@ -325,20 +391,112 @@ data class ObjNamespace(val name: String) : Obj() {
     }
 }
 
-open class ObjError(val context: Context, val message: String) : Obj() {
-    override val asStr: ObjString by lazy { ObjString("Error: $message") }
+open class ObjException(exceptionClass: ExceptionClass, val context: Context, val message: String) : Obj() {
+    constructor(name: String, context: Context, message: String) : this(
+        getOrCreateExceptionClass(name),
+        context,
+        message
+    )
+
+    constructor(context: Context, message: String) : this(Root, context, message)
 
     fun raise(): Nothing {
         throw ExecutionError(this)
     }
+
+    override val objClass: ObjClass = exceptionClass
+
+    override fun toString(): String {
+        return "ObjException:${objClass.className}:${context.pos}@${hashCode().encodeToHex()}"
+    }
+
+    companion object {
+
+        class ExceptionClass(val name: String, vararg parents: ObjClass) : ObjClass(name, *parents) {
+            override suspend fun callOn(context: Context): Obj {
+                val message = context.args.getOrNull(0)?.toString() ?: name
+                return ObjException(this, context, message)
+            }
+
+            override fun toString(): String = "ExceptionClass[$name]@${hashCode().encodeToHex()}"
+        }
+
+        val Root = ExceptionClass("Throwable").apply {
+            addConst("message", statement {
+                (thisObj as ObjException).message.toObj()
+            })
+        }
+
+        private val op = ProtectedOp()
+        private val existingErrorClasses = mutableMapOf<String, ExceptionClass>()
+
+
+        @OptIn(ExperimentalContracts::class)
+        protected fun getOrCreateExceptionClass(name: String): ExceptionClass {
+            return op.withLock {
+                existingErrorClasses.getOrPut(name) {
+                    ExceptionClass(name, Root)
+                }
+            }
+        }
+
+        /**
+         * Get [ObjClass] for error class by name if exists.
+         */
+        @OptIn(ExperimentalContracts::class)
+        fun getErrorClass(name: String): ObjClass? = op.withLock {
+            existingErrorClasses[name]
+        }
+
+        fun addExceptionsToContext(context: Context) {
+            context.addConst("Exception", Root)
+            existingErrorClasses["Exception"] = Root
+            for (name in listOf(
+                "NullReferenceException",
+                "AssertionFailedException",
+                "ClassCastException",
+                "IndexOutOfBoundsException",
+                "IllegalArgumentException",
+                "NoSuchElementException",
+                "IllegalAssignmentException",
+                "SymbolNotDefinedException",
+                "IterationEndException",
+                "AccessException",
+                "UnknownException",
+            )) {
+                context.addConst(name, getOrCreateExceptionClass(name))
+            }
+        }
+    }
 }
 
-class ObjNullPointerError(context: Context) : ObjError(context, "object is null")
+class ObjNullReferenceException(context: Context) : ObjException("NullReferenceException", context, "object is null")
 
-class ObjAssertionError(context: Context, message: String) : ObjError(context, message)
-class ObjClassCastError(context: Context, message: String) : ObjError(context, message)
-class ObjIndexOutOfBoundsError(context: Context, message: String = "index out of bounds") : ObjError(context, message)
-class ObjIllegalArgumentError(context: Context, message: String = "illegal argument") : ObjError(context, message)
-class ObjIllegalAssignmentError(context: Context, message: String = "illegal assignment") : ObjError(context, message)
-class ObjSymbolNotDefinedError(context: Context, message: String = "symbol is not defined") : ObjError(context, message)
-class ObjIterationFinishedError(context: Context) : ObjError(context, "iteration finished")
+class ObjAssertionFailedException(context: Context, message: String) :
+    ObjException("AssertionFailedException", context, message)
+
+class ObjClassCastException(context: Context, message: String) : ObjException("ClassCastException", context, message)
+class ObjIndexOutOfBoundsException(context: Context, message: String = "index out of bounds") :
+    ObjException("IndexOutOfBoundsException", context, message)
+
+class ObjIllegalArgumentException(context: Context, message: String = "illegal argument") :
+    ObjException("IllegalArgumentException", context, message)
+
+@Suppress("unused")
+class ObjNoSuchElementException(context: Context, message: String = "no such element") :
+    ObjException("IllegalArgumentException", context, message)
+
+class ObjIllegalAssignmentException(context: Context, message: String = "illegal assignment") :
+    ObjException("NoSuchElementException", context, message)
+
+class ObjSymbolNotDefinedException(context: Context, message: String = "symbol is not defined") :
+    ObjException("SymbolNotDefinedException", context, message)
+
+class ObjIterationFinishedException(context: Context) :
+    ObjException("IterationEndException", context, "iteration finished")
+
+class ObjAccessException(context: Context, message: String = "access not allowed error") :
+    ObjException("AccessException", context, message)
+
+class ObjUnknownException(context: Context, message: String = "access not allowed error") :
+    ObjException("UnknownException", context, message)

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjArray.kt

@@ -0,0 +1,38 @@
+package net.sergeych.lyng
+
+val ObjArray by lazy {
+
+    /**
+     * Array abstract class is a [ObjCollection] with `getAt` method.
+     */
+    ObjClass("Array", ObjCollection).apply {
+        // we can create iterators using size/getat:
+
+        addFn("iterator") {
+            ObjArrayIterator(thisObj).also { it.init(this) }
+        }
+
+        addFn("contains", isOpen = true) {
+            val obj = args.firstAndOnly()
+            for (i in 0..<thisObj.invokeInstanceMethod(this, "size").toInt()) {
+                if (thisObj.getAt(this, ObjInt(i.toLong())).compareTo(this, obj) == 0) return@addFn ObjTrue
+            }
+            ObjFalse
+        }
+
+        addFn("last") {
+            thisObj.invokeInstanceMethod(
+                this,
+                "getAt",
+                (thisObj.invokeInstanceMethod(this, "size").toInt() - 1).toObj()
+            )
+        }
+
+        addFn("lastIndex") { (thisObj.invokeInstanceMethod(this, "size").toInt() - 1).toObj() }
+
+        addFn("indices") {
+            ObjRange(0.toObj(), thisObj.invokeInstanceMethod(this, "size"), false)
+        }
+
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjArrayIterator.kt

@@ -0,0 +1,32 @@
+package net.sergeych.lyng
+
+class ObjArrayIterator(val array: Obj) : Obj() {
+
+    override val objClass: ObjClass by lazy { type }
+
+    private var nextIndex = 0
+    private var lastIndex = 0
+
+    suspend fun init(context: Context) {
+        nextIndex = 0
+        lastIndex = array.invokeInstanceMethod(context, "size").toInt()
+        ObjVoid
+    }
+
+    companion object {
+        val type by lazy {
+            ObjClass("ArrayIterator", ObjIterator).apply {
+                addFn("next") {
+                    val self = thisAs<ObjArrayIterator>()
+                    if (self.nextIndex < self.lastIndex) {
+                        self.array.invokeInstanceMethod(this, "getAt", (self.nextIndex++).toObj())
+                    } else raiseError(ObjIterationFinishedException(this))
+                }
+                addFn("hasNext") {
+                    val self = thisAs<ObjArrayIterator>()
+                    if (self.nextIndex < self.lastIndex) ObjTrue else ObjFalse
+                }
+            }
+        }
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjBool.kt

@@ -18,6 +18,10 @@ data class ObjBool(val value: Boolean) : Obj() {
 
     override suspend fun logicalOr(context: Context, other: Obj): Obj = ObjBool(value || other.toBool())
 
+    override suspend fun toKotlin(context: Context): Any {
+        return value
+    }
+
     companion object {
         val type = ObjClass("Bool")
     }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjClass.kt

@@ -0,0 +1,73 @@
+package net.sergeych.lyng
+
+val ObjClassType by lazy { ObjClass("Class") }
+
+open class ObjClass(
+    val className: String,
+    vararg val parents: ObjClass,
+) : Obj() {
+
+    var instanceConstructor: Statement? = null
+
+    val allParentsSet: Set<ObjClass> =
+        parents.flatMap {
+            listOf(it) + it.allParentsSet
+        }.toMutableSet()
+
+    override val objClass: ObjClass by lazy { ObjClassType }
+
+    // members: fields most often
+    private val members = mutableMapOf<String, ObjRecord>()
+
+    override fun toString(): String = className
+
+    override suspend fun compareTo(context: Context, other: Obj): Int = if (other === this) 0 else -1
+
+    override suspend fun callOn(context: Context): Obj {
+        val instance = ObjInstance(this)
+        instance.instanceContext = context.copy(newThisObj = instance,args = context.args)
+        if (instanceConstructor != null) {
+            instanceConstructor!!.execute(instance.instanceContext)
+        }
+        return instance
+    }
+
+    fun defaultInstance(): Obj = object : Obj() {
+        override val objClass: ObjClass = this@ObjClass
+    }
+
+    fun createField(
+        name: String,
+        initialValue: Obj,
+        isMutable: Boolean = false,
+        visibility: Visibility = Visibility.Public,
+        pos: Pos = Pos.builtIn
+    ) {
+        val existing = members[name] ?: allParentsSet.firstNotNullOfOrNull { it.members[name] }
+        if( existing?.isMutable == false)
+            throw ScriptError(pos, "$name is already defined in $objClass or one of its supertypes")
+        members[name] = ObjRecord(initialValue, isMutable, visibility)
+    }
+
+    fun addFn(name: String, isOpen: Boolean = false, code: suspend Context.() -> Obj) {
+        createField(name, statement { code() }, isOpen)
+    }
+
+    fun addConst(name: String, value: Obj) = createField(name, value, isMutable = false)
+
+
+    /**
+     * Get instance member traversing the hierarchy if needed. Its meaning is different for different objects.
+     */
+    fun getInstanceMemberOrNull(name: String): ObjRecord? {
+        members[name]?.let { return it }
+        allParentsSet.forEach { parent -> parent.getInstanceMemberOrNull(name)?.let { return it } }
+        return rootObjectType.members[name]
+    }
+
+    fun getInstanceMember(atPos: Pos, name: String): ObjRecord =
+        getInstanceMemberOrNull(name)
+            ?: throw ScriptError(atPos, "symbol doesn't exist: $name")
+}
+
+

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjCollection.kt

@@ -0,0 +1,8 @@
+package net.sergeych.lyng
+
+/**
+ * Collection is an iterator with `size`]
+ */
+val ObjCollection = ObjClass("Collection", ObjIterable).apply {
+
+    }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjInstance.kt

@@ -0,0 +1,55 @@
+package net.sergeych.lyng
+
+class ObjInstance(override val objClass: ObjClass) : Obj() {
+
+    internal lateinit var instanceContext: Context
+
+    override suspend fun readField(context: Context, name: String): ObjRecord {
+        return instanceContext[name]?.let {
+            if (it.visibility.isPublic)
+                it
+            else
+                context.raiseError(ObjAccessException(context, "can't access non-public field $name"))
+        }
+            ?: super.readField(context, name)
+    }
+
+    override suspend fun writeField(context: Context, name: String, newValue: Obj) {
+        instanceContext[name]?.let { f ->
+            if (!f.visibility.isPublic)
+                ObjIllegalAssignmentException(context, "can't assign to non-public field $name")
+            if (!f.isMutable) ObjIllegalAssignmentException(context, "can't reassign val $name").raise()
+            if (f.value.assign(context, newValue) == null)
+                f.value = newValue
+        } ?: super.writeField(context, name, newValue)
+    }
+
+    override suspend fun invokeInstanceMethod(context: Context, name: String, args: Arguments): Obj =
+        instanceContext[name]?.let {
+            if (it.visibility.isPublic)
+                it.value.invoke(context, this, args)
+            else
+                context.raiseError(ObjAccessException(context, "can't invoke non-public method $name"))
+        }
+            ?: super.invokeInstanceMethod(context, name, args)
+
+    private val publicFields: Map<String, ObjRecord>
+        get() = instanceContext.objects.filter { it.value.visibility.isPublic }
+
+    override fun toString(): String {
+        val fields = publicFields.map { "${it.key}=${it.value.value}" }.joinToString(",")
+        return "${objClass.className}($fields)"
+    }
+
+    override suspend fun compareTo(context: Context, other: Obj): Int {
+        if (other !is ObjInstance) return -1
+        if (other.objClass != objClass) return -1
+        for (f in publicFields) {
+            val a = f.value.value
+            val b = other.instanceContext[f.key]!!.value
+            val d = a.compareTo(context, b)
+            if (d != 0) return d
+        }
+        return 0
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjInt.kt

@@ -9,6 +9,10 @@ data class ObjInt(var value: Long) : Obj(), Numeric {
 
     override fun byValueCopy(): Obj = ObjInt(value)
 
+    override fun hashCode(): Int {
+        return value.hashCode()
+    }
+
     override suspend fun getAndIncrement(context: Context): Obj {
         return ObjInt(value).also { value++ }
     }
@@ -72,7 +76,22 @@ data class ObjInt(var value: Long) : Obj(), Numeric {
         } else null
     }
 
+    override suspend fun toKotlin(context: Context): Any {
+        return value
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other == null || this::class != other::class) return false
+
+        other as ObjInt
+
+        return value == other.value
+    }
+
     companion object {
+        val Zero = ObjInt(0)
+        val One = ObjInt(1)
         val type = ObjClass("Int")
     }
 }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjIterable.kt

@@ -0,0 +1,89 @@
+package net.sergeych.lyng
+
+/**
+ * Abstract class that must provide `iterator` method that returns [ObjIterator] instance.
+ */
+val ObjIterable by lazy {
+    ObjClass("Iterable").apply {
+
+        addFn("toList") {
+            val result = mutableListOf<Obj>()
+            val iterator = thisObj.invokeInstanceMethod(this, "iterator")
+
+            while (iterator.invokeInstanceMethod(this, "hasNext").toBool())
+                result += iterator.invokeInstanceMethod(this, "next")
+            ObjList(result)
+        }
+
+        // it is not effective, but it is open:
+        addFn("contains", isOpen = true) {
+            val obj = args.firstAndOnly()
+            val it = thisObj.invokeInstanceMethod(this, "iterator")
+            while (it.invokeInstanceMethod(this, "hasNext").toBool()) {
+                if (obj.compareTo(this, it.invokeInstanceMethod(this, "next")) == 0)
+                    return@addFn ObjTrue
+            }
+            ObjFalse
+        }
+
+        addFn("indexOf", isOpen = true) {
+            val obj = args.firstAndOnly()
+            var index = 0
+            val it = thisObj.invokeInstanceMethod(this, "iterator")
+            while (it.invokeInstanceMethod(this, "hasNext").toBool()) {
+                if (obj.compareTo(this, it.invokeInstanceMethod(this, "next")) == 0)
+                    return@addFn ObjInt(index.toLong())
+                index++
+            }
+            ObjInt(-1L)
+        }
+
+        addFn("toSet") {
+            val result = mutableSetOf<Obj>()
+            val it = thisObj.invokeInstanceMethod(this, "iterator")
+            while (it.invokeInstanceMethod(this, "hasNext").toBool()) {
+                result += it.invokeInstanceMethod(this, "next")
+            }
+            ObjSet(result)
+        }
+
+        addFn("toMap") {
+            val result = mutableListOf<Obj>()
+            val it = thisObj.invokeInstanceMethod(this, "iterator")
+            while (it.invokeInstanceMethod(this, "hasNext").toBool()) {
+                result += it.invokeInstanceMethod(this, "next")
+            }
+            ObjMap(ObjMap.listToMap(this, result))
+        }
+
+        addFn("forEach", isOpen = true) {
+            val it = thisObj.invokeInstanceMethod(this, "iterator")
+            val fn = requiredArg<Statement>(0)
+            while (it.invokeInstanceMethod(this, "hasNext").toBool()) {
+                val x = it.invokeInstanceMethod(this, "next")
+                fn.execute(this.copy(Arguments(listOf(x))))
+            }
+            ObjVoid
+        }
+
+        addFn("map", isOpen = true) {
+            val it = thisObj.invokeInstanceMethod(this, "iterator")
+            val fn = requiredArg<Statement>(0)
+            val result = mutableListOf<Obj>()
+            while (it.invokeInstanceMethod(this, "hasNext").toBool()) {
+                val x = it.invokeInstanceMethod(this, "next")
+                result += fn.execute(this.copy(Arguments(listOf(x))))
+            }
+            ObjList(result)
+        }
+
+        addFn("isEmpty") {
+            ObjBool(
+                thisObj.invokeInstanceMethod(this, "iterator")
+                    .invokeInstanceMethod(this, "hasNext").toBool()
+                    .not()
+            )
+        }
+
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjIterator.kt

@@ -0,0 +1,3 @@
+package net.sergeych.lyng
+
+val ObjIterator by lazy { ObjClass("Iterator") }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjKotlinIterator.kt

@@ -0,0 +1,39 @@
+@file:Suppress("unused")
+
+package net.sergeych.lyng
+
+/**
+ * Iterator wrapper to allow Kotlin collections to be returned from Lyng objects;
+ * each object is converted to a Lyng object.
+ */
+class ObjKotlinIterator(val iterator: Iterator<Any?>) : Obj() {
+
+    override val objClass = type
+
+    companion object {
+        val type = ObjClass("KotlinIterator", ObjIterator).apply {
+            addFn("next") { thisAs<ObjKotlinIterator>().iterator.next().toObj() }
+            addFn("hasNext") { thisAs<ObjKotlinIterator>().iterator.hasNext().toObj() }
+        }
+
+    }
+}
+
+/**
+ * Propagate kotlin iterator that already produces Lyng objects, no conversion
+ * is applied
+ */
+class ObjKotlinObjIterator(val iterator: Iterator<Obj>) : Obj() {
+
+    override val objClass = type
+
+    companion object {
+        val type = ObjClass("KotlinIterator", ObjIterator).apply {
+            addFn("next") {
+                thisAs<ObjKotlinObjIterator>().iterator.next()
+            }
+            addFn("hasNext") { thisAs<ObjKotlinIterator>().iterator.hasNext().toObj() }
+        }
+
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjList.kt

@@ -0,0 +1,230 @@
+package net.sergeych.lyng
+
+class ObjList(val list: MutableList<Obj> = mutableListOf()) : Obj() {
+
+    init {
+        for (p in objClass.parents)
+            parentInstances.add(p.defaultInstance())
+    }
+
+    override fun toString(): String = "[${
+        list.joinToString(separator = ", ") { it.inspect() }
+    }]"
+
+    override suspend fun getAt(context: Context, index: Obj): Obj {
+        return when (index) {
+            is ObjInt -> {
+                list[index.toInt()]
+            }
+
+            is ObjRange -> {
+                when {
+                    index.start is ObjInt && index.end is ObjInt -> {
+                        if (index.isEndInclusive)
+                            ObjList(list.subList(index.start.toInt(), index.end.toInt() + 1).toMutableList())
+                        else
+                            ObjList(list.subList(index.start.toInt(), index.end.toInt()).toMutableList())
+                    }
+
+                    index.isOpenStart && !index.isOpenEnd -> {
+                        if (index.isEndInclusive)
+                            ObjList(list.subList(0, index.end!!.toInt() + 1).toMutableList())
+                        else
+                            ObjList(list.subList(0, index.end!!.toInt()).toMutableList())
+                    }
+
+                    index.isOpenEnd && !index.isOpenStart -> {
+                        ObjList(list.subList(index.start!!.toInt(), list.size).toMutableList())
+                    }
+
+                    index.isOpenStart && index.isOpenEnd -> {
+                        ObjList(list.toMutableList())
+                    }
+
+                    else -> {
+                        throw RuntimeException("Can't apply range for index: $index")
+                    }
+                }
+            }
+
+            else -> context.raiseIllegalArgument("Illegal index object for a list: ${index.inspect()}")
+        }
+    }
+
+    override suspend fun putAt(context: Context, index: Int, newValue: Obj) {
+        val i = index
+        list[i] = newValue
+    }
+
+    override suspend fun compareTo(context: Context, other: Obj): Int {
+        if (other !is ObjList) return -2
+        val mySize = list.size
+        val otherSize = other.list.size
+        val commonSize = minOf(mySize, otherSize)
+        for (i in 0..<commonSize) {
+            if (list[i].compareTo(context, other.list[i]) != 0) {
+                return list[i].compareTo(context, other.list[i])
+            }
+        }
+        // equal so far, longer is greater:
+        return when {
+            mySize < otherSize -> -1
+            mySize > otherSize -> 1
+            else -> 0
+        }
+    }
+
+    override suspend fun plus(context: Context, other: Obj): Obj =
+        when {
+            other is ObjList ->
+                ObjList((list + other.list).toMutableList())
+
+            other.isInstanceOf(ObjIterable) -> {
+                val l = other.callMethod<ObjList>(context, "toList")
+                ObjList((list + l.list).toMutableList())
+            }
+
+            else ->
+                context.raiseError("'+': can't concatenate $this with $other")
+        }
+
+
+    override suspend fun plusAssign(context: Context, other: Obj): Obj {
+        // optimization
+        if (other is ObjList) {
+            list += other.list
+            return this
+        }
+        if (other.isInstanceOf(ObjIterable)) {
+            val otherList = other.invokeInstanceMethod(context, "toList") as ObjList
+            list += otherList.list
+        } else
+            list += other
+        return this
+    }
+
+    override suspend fun contains(context: Context, other: Obj): Boolean {
+        return list.contains(other)
+    }
+
+    override val objClass: ObjClass
+        get() = type
+
+    override suspend fun toKotlin(context: Context): Any {
+        return list.map { it.toKotlin(context) }
+    }
+
+    override fun hashCode(): Int {
+        // check?
+        return list.hashCode()
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other == null || this::class != other::class) return false
+
+        other as ObjList
+
+        return list == other.list
+    }
+
+    companion object {
+        val type = ObjClass("List", ObjArray).apply {
+
+            createField("size",
+                statement {
+                    (thisObj as ObjList).list.size.toObj()
+                }
+            )
+            addFn("getAt") {
+                requireExactCount(1)
+                thisAs<ObjList>().getAt(this, requiredArg<Obj>(0))
+            }
+            addFn("putAt") {
+                requireExactCount(2)
+                val newValue = args[1]
+                thisAs<ObjList>().putAt(this, requiredArg<ObjInt>(0).value.toInt(), newValue)
+                newValue
+            }
+            createField("add",
+                statement {
+                    val l = thisAs<ObjList>().list
+                    for (a in args) l.add(a)
+                    ObjVoid
+                }
+            )
+            addFn("insertAt") {
+                if (args.size < 2) raiseError("addAt takes 2+ arguments")
+                val l = thisAs<ObjList>()
+                var index = requiredArg<ObjInt>(0).value.toInt()
+                for (i in 1..<args.size) l.list.add(index++, args[i])
+                ObjVoid
+            }
+
+            addFn("removeAt") {
+                val self = thisAs<ObjList>()
+                val start = requiredArg<ObjInt>(0).value.toInt()
+                if (args.size == 2) {
+                    val end = requireOnlyArg<ObjInt>().value.toInt()
+                    self.list.subList(start, end).clear()
+                } else
+                    self.list.removeAt(start)
+                self
+            }
+
+            addFn("removeLast") {
+                val self = thisAs<ObjList>()
+                if (args.isNotEmpty()) {
+                    val count = requireOnlyArg<ObjInt>().value.toInt()
+                    val size = self.list.size
+                    if (count >= size) self.list.clear()
+                    else self.list.subList(size - count, size).clear()
+                } else self.list.removeLast()
+                self
+            }
+
+            addFn("removeRange") {
+                val self = thisAs<ObjList>()
+                val list = self.list
+                val range = requiredArg<Obj>(0)
+                if (range is ObjRange) {
+                    val index = range
+                    when {
+                        index.start is ObjInt && index.end is ObjInt -> {
+                            if (index.isEndInclusive)
+                                list.subList(index.start.toInt(), index.end.toInt() + 1)
+                            else
+                                list.subList(index.start.toInt(), index.end.toInt())
+                        }
+
+                        index.isOpenStart && !index.isOpenEnd -> {
+                            if (index.isEndInclusive)
+                                list.subList(0, index.end!!.toInt() + 1)
+                            else
+                                list.subList(0, index.end!!.toInt())
+                        }
+
+                        index.isOpenEnd && !index.isOpenStart -> {
+                            list.subList(index.start!!.toInt(), list.size)
+                        }
+
+                        index.isOpenStart && index.isOpenEnd -> {
+                            list
+                        }
+
+                        else -> {
+                            throw RuntimeException("Can't apply range for index: $index")
+                        }
+                    }.clear()
+                } else {
+                    val start = range.toInt()
+                    val end = requiredArg<ObjInt>(1).value.toInt() + 1
+                    self.list.subList(start, end).clear()
+                }
+                self
+            }
+        }
+    }
+}
+
+

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjMap.kt

@@ -0,0 +1,114 @@
+package net.sergeych.lyng
+
+class ObjMapEntry(val key: Obj, val value: Obj) : Obj() {
+
+    override suspend fun compareTo(context: Context, other: Obj): Int {
+        if (other !is ObjMapEntry) return -1
+        val c = key.compareTo(context, other.key)
+        if (c != 0) return c
+        return value.compareTo(context, other.value)
+    }
+
+    override suspend fun getAt(context: Context, index: Obj): Obj = when (index.toInt()) {
+        0 -> key
+        1 -> value
+        else -> context.raiseIndexOutOfBounds()
+    }
+
+    override fun toString(): String {
+        return "$key=>$value"
+    }
+
+    override val objClass = type
+
+    companion object {
+        val type = object : ObjClass("MapEntry", ObjArray) {
+            override suspend fun callOn(context: Context): Obj {
+                return ObjMapEntry(context.requiredArg<Obj>(0), context.requiredArg<Obj>(1))
+            }
+        }.apply {
+            addFn("key") { thisAs<ObjMapEntry>().key }
+            addFn("value") { thisAs<ObjMapEntry>().value }
+            addFn("size") { 2.toObj() }
+        }
+    }
+}
+
+class ObjMap(val map: MutableMap<Obj, Obj>) : Obj() {
+
+    override val objClass = type
+
+    override suspend fun getAt(context: Context, index: Obj): Obj =
+        map.getOrElse(index) { context.raiseNoSuchElement() }
+
+    override suspend fun contains(context: Context, other: Obj): Boolean {
+        return other in map
+    }
+
+    override suspend fun compareTo(context: Context, other: Obj): Int {
+        if( other is ObjMap && other.map == map) return 0
+        return -1
+    }
+    override fun toString(): String = map.toString()
+
+    companion object {
+
+        suspend fun listToMap(context: Context, list: List<Obj>): MutableMap<Obj, Obj> {
+            val map = mutableMapOf<Obj, Obj>()
+            if (list.isEmpty()) return map
+
+            val first = list.first()
+            if (first.isInstanceOf(ObjArray)) {
+                if (first.invokeInstanceMethod(context, "size").toInt() != 2)
+                    context.raiseIllegalArgument(
+                        "list to construct map entry should exactly be 2 element Array like [key,value], got $list"
+                    )
+            } else context.raiseIllegalArgument("first element of map list be a Collection of 2 elements; got $first")
+
+
+
+            list.forEach {
+                map[it.getAt(context, ObjInt.Zero)] = it.getAt(context, ObjInt.One)
+            }
+            return map
+        }
+
+
+        val type = object : ObjClass("Map", ObjCollection) {
+            override suspend fun callOn(context: Context): Obj {
+                return ObjMap(listToMap(context, context.args.list))
+            }
+        }.apply {
+            addFn("getOrNull") {
+                val key = args.firstAndOnly(pos)
+                thisAs<ObjMap>().map.getOrElse(key) { ObjNull }
+            }
+            addFn("getOrPut") {
+                val key = requiredArg<Obj>(0)
+                thisAs<ObjMap>().map.getOrPut(key) {
+                    val lambda = requiredArg<Statement>(1)
+                    lambda.execute(this)
+                }
+            }
+            addFn("size") {
+                thisAs<ObjMap>().map.size.toObj()
+            }
+            addFn("remove") {
+                thisAs<ObjMap>().map.remove(requiredArg<Obj>(0))?.toObj() ?: ObjNull
+            }
+            addFn("clear") {
+                thisAs<ObjMap>().map.clear()
+                thisObj
+            }
+            addFn("keys") {
+                thisAs<ObjMap>().map.keys.toObj()
+            }
+            addFn("values") {
+                ObjList(thisAs<ObjMap>().map.values.toMutableList())
+            }
+            addFn("iterator") {
+                ObjKotlinIterator(thisAs<ObjMap>().map.entries.iterator())
+            }
+        }
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjRange.kt

@@ -2,6 +2,9 @@ package net.sergeych.lyng
 
 class ObjRange(val start: Obj?, val end: Obj?, val isEndInclusive: Boolean) : Obj() {
 
+    val isOpenStart by lazy { start == null || start.isNull }
+    val isOpenEnd by lazy { end == null || end.isNull }
+
     override val objClass: ObjClass = type
 
     override fun toString(): String {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjRangeIterator.kt

@@ -33,7 +33,7 @@ class ObjRangeIterator(val self: ObjRange) : Obj() {
             if( isCharRange ) ObjChar(x.toInt().toChar()) else ObjInt(x)
         }
         else {
-            context.raiseError(ObjIterationFinishedError(context))
+            context.raiseError(ObjIterationFinishedException(context))
         }
 
     companion object {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjReal.kt

@@ -10,6 +10,8 @@ data class ObjReal(val value: Double) : Obj(), Numeric {
     override val toObjInt: ObjInt by lazy { ObjInt(longValue) }
     override val toObjReal: ObjReal by lazy { ObjReal(value) }
 
+    override val objClass: ObjClass = type
+
     override fun byValueCopy(): Obj = ObjReal(value)
 
     override suspend fun compareTo(context: Context, other: Obj): Int {
@@ -19,7 +21,9 @@ data class ObjReal(val value: Double) : Obj(), Numeric {
 
     override fun toString(): String = value.toString()
 
-    override val objClass: ObjClass = type
+    override fun hashCode(): Int {
+        return value.hashCode()
+    }
 
     override suspend fun plus(context: Context, other: Obj): Obj =
         ObjReal(this.value + other.toDouble())
@@ -36,6 +40,22 @@ data class ObjReal(val value: Double) : Obj(), Numeric {
     override suspend fun mod(context: Context, other: Obj): Obj =
         ObjReal(this.value % other.toDouble())
 
+    /**
+     * Returns unboxed Double value
+     */
+    override suspend fun toKotlin(context: Context): Any {
+        return value
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other == null || this::class != other::class) return false
+
+        other as ObjReal
+
+        return value == other.value
+    }
+
     companion object {
         val type: ObjClass = ObjClass("Real").apply {
             createField(

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjSet.kt

@@ -0,0 +1,99 @@
+package net.sergeych.lyng
+
+class ObjSet(val set: MutableSet<Obj> = mutableSetOf()) : Obj() {
+
+    override val objClass = type
+
+    override suspend fun contains(context: Context, other: Obj): Boolean {
+        return set.contains(other)
+    }
+
+    override suspend fun plus(context: Context, other: Obj): Obj {
+        return ObjSet(
+            if (other is ObjSet)
+                (set + other.set).toMutableSet()
+            else
+                (set + other).toMutableSet()
+        )
+    }
+
+    override suspend fun plusAssign(context: Context, other: Obj): Obj {
+        when (other) {
+            is ObjSet -> {
+                set += other.set
+            }
+
+            is ObjList -> {
+                set += other.list
+            }
+
+            else -> {
+                if (other.isInstanceOf(ObjIterable)) {
+                    val i = other.invokeInstanceMethod(context, "iterable")
+                    while (i.invokeInstanceMethod(context, "hasNext").toBool()) {
+                        set += i.invokeInstanceMethod(context, "next")
+                    }
+                }
+                set += other
+            }
+        }
+        return this
+    }
+
+    override suspend fun mul(context: Context, other: Obj): Obj {
+        return if (other is ObjSet) {
+            ObjSet(set.intersect(other.set).toMutableSet())
+        } else
+            context.raiseIllegalArgument("set operator * requires another set")
+    }
+
+    override suspend fun minus(context: Context, other: Obj): Obj {
+        if (other !is ObjSet)
+            context.raiseIllegalArgument("set operator - requires another set")
+        return ObjSet(set.minus(other.set).toMutableSet())
+    }
+
+    override fun toString(): String {
+        return "Set(${set.joinToString(", ")})"
+    }
+
+    override suspend fun compareTo(context: Context, other: Obj): Int {
+        return if (other !is ObjSet) -1
+        else {
+            if (set == other.set) 0
+            else -1
+        }
+    }
+
+    companion object {
+
+
+        val type = object : ObjClass("Set", ObjCollection) {
+            override suspend fun callOn(context: Context): Obj {
+                return ObjSet(context.args.list.toMutableSet())
+            }
+        }.apply {
+            addFn("size") {
+                thisAs<ObjSet>().set.size.toObj()
+            }
+            addFn("intersect") {
+                thisAs<ObjSet>().mul(this, args.firstAndOnly())
+            }
+            addFn("iterator") {
+                thisAs<ObjSet>().set.iterator().toObj()
+            }
+            addFn("union") {
+                thisAs<ObjSet>().plus(this, args.firstAndOnly())
+            }
+            addFn("subtract") {
+                thisAs<ObjSet>().minus(this, args.firstAndOnly())
+            }
+            addFn("remove") {
+                val set = thisAs<ObjSet>().set
+                val n = set.size
+                for( x in args.list ) set -= x
+                if( n == set.size ) ObjFalse else ObjTrue
+            }
+        }
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ObjString.kt

@@ -0,0 +1,117 @@
+package net.sergeych.lyng
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import net.sergeych.sprintf.sprintf
+
+@Serializable
+@SerialName("string")
+data class ObjString(val value: String) : Obj() {
+
+//    fun normalize(context: Context, index: Int, allowsEndInclusive: Boolean = false): Int {
+//        val i = if (index < 0) value.length + index else index
+//        if (allowsEndInclusive && i == value.length) return i
+//        if (i !in value.indices) context.raiseError("index $index out of bounds for length ${value.length} of \"$value\"")
+//        return i
+//    }
+
+
+    override suspend fun compareTo(context: Context, other: Obj): Int {
+        if (other !is ObjString) return -2
+        return this.value.compareTo(other.value)
+    }
+
+    override fun toString(): String = value
+
+    override val asStr: ObjString by lazy { this }
+
+    override fun inspect(): String {
+        return "\"$value\""
+    }
+
+    override val objClass: ObjClass
+        get() = type
+
+    override suspend fun plus(context: Context, other: Obj): Obj {
+        return ObjString(value + other.asStr.value)
+    }
+
+    override suspend fun getAt(context: Context, index: Obj): Obj {
+        if( index is ObjInt ) return ObjChar(value[index.toInt()])
+        if( index is ObjRange ) {
+            val start = if(index.start == null || index.start.isNull) 0 else  index.start.toInt()
+            val end = if( index.end  == null || index.end.isNull ) value.length else  {
+                val e = index.end.toInt()
+                if( index.isEndInclusive) e + 1 else e
+            }
+            return ObjString(value.substring(start, end))
+        }
+        context.raiseIllegalArgument("String index must be Int or Range")
+    }
+
+    override fun hashCode(): Int {
+        return value.hashCode()
+    }
+
+    override suspend fun callOn(context: Context): Obj {
+        return ObjString(this.value.sprintf(*context.args.toKotlinList(context).toTypedArray()))
+    }
+
+    override suspend fun contains(context: Context, other: Obj): Boolean {
+        return if (other is ObjString)
+            value.contains(other.value)
+        else if (other is ObjChar)
+            value.contains(other.value)
+        else context.raiseIllegalArgument("String.contains can't take $other")
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other == null || this::class != other::class) return false
+
+        other as ObjString
+
+        return value == other.value
+    }
+
+    companion object {
+        val type = ObjClass("String").apply {
+            addFn("startsWith") {
+                ObjBool(thisAs<ObjString>().value.startsWith(requiredArg<ObjString>(0).value))
+            }
+            addFn("endsWith") {
+                ObjBool(thisAs<ObjString>().value.endsWith(requiredArg<ObjString>(0).value))
+            }
+            addConst("length",
+                statement { ObjInt(thisAs<ObjString>().value.length.toLong()) }
+            )
+            addFn("takeLast") {
+                thisAs<ObjString>().value.takeLast(
+                    requiredArg<ObjInt>(0).toInt()
+                ).let(::ObjString)
+            }
+            addFn("take") {
+                thisAs<ObjString>().value.take(
+                    requiredArg<ObjInt>(0).toInt()
+                ).let(::ObjString)
+            }
+            addFn("drop") {
+                thisAs<ObjString>().value.drop(
+                    requiredArg<ObjInt>(0).toInt()
+                ).let(::ObjString)
+            }
+            addFn("dropLast") {
+                thisAs<ObjString>().value.dropLast(
+                    requiredArg<ObjInt>(0).toInt()
+                ).let(::ObjString)
+            }
+            addFn("lower") {
+                thisAs<ObjString>().value.lowercase().let(::ObjString)
+            }
+            addFn("upper") {
+                thisAs<ObjString>().value.uppercase().let(::ObjString)
+            }
+            addFn("size") { ObjInt(thisAs<ObjString>().value.length.toLong()) }
+        }
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Parser.kt

@@ -45,12 +45,18 @@ private class Parser(fromPos: Pos) {
             '=' -> {
                 if (pos.currentChar == '=') {
                     pos.advance()
-                    if (currentChar == '=') {
-                        pos.advance()
-                        Token("===", from, Token.Type.REF_EQ)
-                    } else
-                        Token("==", from, Token.Type.EQ)
-                } else
+                    when (currentChar) {
+                        '=' -> {
+                            pos.advance()
+                            Token("===", from, Token.Type.REF_EQ)
+                        }
+                        else -> Token("==", from, Token.Type.EQ)
+                    }
+                } else if( currentChar == '>' ) {
+                    pos.advance()
+                    Token("=>", from, Token.Type.EQARROW)
+                }
+                else
                     Token("=", from, Token.Type.ASSIGN)
             }
 
@@ -137,14 +143,20 @@ private class Parser(fromPos: Pos) {
                 if (currentChar == '.') {
                     pos.advance()
                     // .. already parsed:
-                    if (currentChar == '.') {
-                        pos.advance()
-                        Token("...", from, Token.Type.ELLIPSIS)
-                    } else if (currentChar == '<') {
-                        pos.advance()
-                        Token("..<", from, Token.Type.DOTDOTLT)
-                    } else {
-                        Token("..", from, Token.Type.DOTDOT)
+                    when (currentChar) {
+                        '.' -> {
+                            pos.advance()
+                            Token("...", from, Token.Type.ELLIPSIS)
+                        }
+
+                        '<' -> {
+                            pos.advance()
+                            Token("..<", from, Token.Type.DOTDOTLT)
+                        }
+
+                        else -> {
+                            Token("..", from, Token.Type.DOTDOT)
+                        }
                     }
                 } else
                     Token(".", from, Token.Type.DOT)
@@ -153,11 +165,10 @@ private class Parser(fromPos: Pos) {
             '<' -> {
                 if (currentChar == '=') {
                     pos.advance()
-                    if( currentChar == '>' ) {
+                    if (currentChar == '>') {
                         pos.advance()
                         Token("<=>", from, Token.Type.SHUTTLE)
-                    }
-                    else {
+                    } else {
                         Token("<=", from, Token.Type.LTE)
                     }
                 } else
@@ -236,6 +247,7 @@ private class Parser(fromPos: Pos) {
             }
 
             '"' -> loadStringToken()
+
             in digitsSet -> {
                 pos.back()
                 decodeNumber(loadChars(digits), from)
@@ -261,6 +273,21 @@ private class Parser(fromPos: Pos) {
                 Token(value.toString(), start, Token.Type.CHAR)
             }
 
+            '?' -> {
+                when(currentChar.also { pos.advance() }) {
+                    ':' -> Token("??", from, Token.Type.ELVIS)
+                    '?' -> Token("??", from, Token.Type.ELVIS)
+                    '.' -> Token("?.", from, Token.Type.NULL_COALESCE)
+                    '[' -> Token("?(", from, Token.Type.NULL_COALESCE_INDEX)
+                    '(' -> Token("?(", from, Token.Type.NULL_COALESCE_INVOKE)
+                    '{' -> Token("?{", from, Token.Type.NULL_COALESCE_BLOCKINVOKE)
+                    else -> {
+                        pos.back()
+                        Token("?", from, Token.Type.QUESTION)
+                    }
+                }
+            }
+
             else -> {
                 // text infix operators:
                 // Labels processing is complicated!
@@ -291,7 +318,19 @@ private class Parser(fromPos: Pos) {
     private fun decodeNumber(p1: String, start: Pos): Token =
         if (pos.end)
             Token(p1, start, Token.Type.INT)
-        else if (currentChar == '.') {
+        else if (currentChar == 'e' || currentChar == 'E') {
+            pos.advance()
+            var negative = false
+            if (currentChar == '+')
+                pos.advance()
+            else if (currentChar == '-') {
+                negative = true
+                pos.advance()
+            }
+            var p3 = loadChars(digits)
+            if (negative) p3 = "-$p3"
+            Token("${p1}e$p3", start, Token.Type.REAL)
+        } else if (currentChar == '.') {
             // could be decimal
             pos.advance()
             if (currentChar in digitsSet) {
@@ -324,7 +363,7 @@ private class Parser(fromPos: Pos) {
             // could be integer, also hex:
             if (currentChar == 'x' && p1 == "0") {
                 pos.advance()
-                Token(loadChars({ it in hexDigits }), start, Token.Type.HEX).also {
+                Token(loadChars { it in hexDigits }, start, Token.Type.HEX).also {
                     if (currentChar.isLetter())
                         raise("invalid hex literal")
                 }
@@ -337,10 +376,11 @@ private class Parser(fromPos: Pos) {
     private val currentChar: Char get() = pos.currentChar
 
     private fun loadStringToken(): Token {
-        var start = currentPos
+        val start = currentPos
 
-        if (currentChar == '"') pos.advance()
-        else start = start.back()
+//        if (currentChar == '"') pos.advance()
+//        else start = start.back()
+//        start = start.back()
 
         val sb = StringBuilder()
         while (currentChar != '"') {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Pos.kt

@@ -5,6 +5,7 @@ data class Pos(val source: Source, val line: Int, val column: Int) {
         return "${source.fileName}:${line+1}:${column}"
     }
 
+    @Suppress("unused")
     fun back(): Pos =
         if( column > 0) Pos(source, line, column-1)
         else if( line > 0) Pos(source, line-1, source.lines[line-1].length - 1)

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt

@@ -6,6 +6,7 @@ import kotlin.math.*
 class Script(
     override val pos: Pos,
     private val statements: List<Statement> = emptyList(),
+//    private val catchReturn: Boolean = false,
 ) : Statement() {
 
     override suspend fun execute(context: Context): Obj {
@@ -16,10 +17,11 @@ class Script(
         return lastResult
     }
 
-    suspend fun execute() = execute(defaultContext.copy(pos))
+    suspend fun execute() = execute(defaultContext.copy(pos = pos))
 
     companion object {
         val defaultContext: Context = Context().apply {
+            ObjException.addExceptionsToContext(this)
             addFn("println") {
                 for ((i, a) in args.withIndex()) {
                     if (i > 0) print(' ' + a.asStr.value)
@@ -116,14 +118,14 @@ class Script(
             addVoidFn("assert") {
                 val cond = requiredArg<ObjBool>(0)
                 if( !cond.value == true )
-                    raiseError(ObjAssertionError(this,"Assertion failed"))
+                    raiseError(ObjAssertionFailedException(this,"Assertion failed"))
             }
 
             addVoidFn("assertEquals") {
                 val a = requiredArg<Obj>(0)
                 val b = requiredArg<Obj>(1)
                 if( a.compareTo(this, b) != 0 )
-                    raiseError(ObjAssertionError(this,"Assertion failed: ${a.inspect()} == ${b.inspect()}"))
+                    raiseError(ObjAssertionFailedException(this,"Assertion failed: ${a.inspect()} == ${b.inspect()}"))
             }
             addFn("assertThrows") {
                 val code = requireOnlyArg<Statement>()
@@ -137,33 +139,39 @@ class Script(
                 catch (e: ScriptError) {
                     ObjNull
                 }
-                result ?: raiseError(ObjAssertionError(this,"Expected exception but nothing was thrown"))
+                result ?: raiseError(ObjAssertionFailedException(this,"Expected exception but nothing was thrown"))
             }
 
             addVoidFn("delay") {
                 delay((this.args.firstAndOnly().toDouble()/1000.0).roundToLong())
             }
 
+            addConst("Object", rootObjectType)
             addConst("Real", ObjReal.type)
             addConst("String", ObjString.type)
             addConst("Int", ObjInt.type)
             addConst("Bool", ObjBool.type)
             addConst("Char", ObjChar.type)
             addConst("List", ObjList.type)
+            addConst("Set", ObjSet.type)
             addConst("Range", ObjRange.type)
+            addConst("Map", ObjMap.type)
+            addConst("MapEntry", ObjMapEntry.type)
             @Suppress("RemoveRedundantQualifierName")
             addConst("Callable", Statement.type)
             // interfaces
             addConst("Iterable", ObjIterable)
+            addConst("Collection", ObjCollection)
             addConst("Array", ObjArray)
             addConst("Class", ObjClassType)
-            addConst("Object", Obj().objClass)
 
             val pi = ObjReal(PI)
             addConst("π", pi)
             getOrCreateNamespace("Math").apply {
                 addConst("PI", pi)
             }
+
+
         }
     }
 }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ScriptError.kt

@@ -12,4 +12,4 @@ open class ScriptError(val pos: Pos, val errorMessage: String,cause: Throwable?=
     cause
 )
 
-class ExecutionError(val errorObject: ObjError) : ScriptError(errorObject.context.pos, errorObject.message)
+class ExecutionError(val errorObject: ObjException) : ScriptError(errorObject.context.pos, errorObject.message)

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Token.kt

@@ -14,12 +14,18 @@ data class Token(val value: String, val pos: Pos, val type: Type) {
         IN, NOTIN, IS, NOTIS,
         EQ, NEQ, LT, LTE, GT, GTE, REF_EQ, REF_NEQ,
         SHUTTLE,
-        AND, BITAND, OR, BITOR, NOT, BITNOT, DOT, ARROW, QUESTION, COLONCOLON,
+        AND, BITAND, OR, BITOR, NOT, BITNOT, DOT, ARROW, EQARROW, QUESTION, COLONCOLON,
         SINLGE_LINE_COMMENT, MULTILINE_COMMENT,
         LABEL, ATLABEL, // label@ at@label
+        //PUBLIC, PROTECTED, INTERNAL, EXPORT, OPEN, INLINE, OVERRIDE, ABSTRACT, SEALED, EXTERNAL, VAL, VAR, CONST, TYPE, FUN, CLASS, INTERFACE, ENUM, OBJECT, TRAIT, THIS,
         ELLIPSIS, DOTDOT, DOTDOTLT,
         NEWLINE,
         EOF,
+        NULL_COALESCE,
+        ELVIS,
+        NULL_COALESCE_INDEX,
+        NULL_COALESCE_INVOKE,
+        NULL_COALESCE_BLOCKINVOKE,
     }
 
     companion object {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/TypeDecl.kt

@@ -0,0 +1,14 @@
+@file:Suppress("unused")
+
+package net.sergeych.lyng
+
+// this is highly experimental and subject to complete redesign
+// very soon
+sealed class TypeDecl(val isNullable:Boolean = false) {
+    // ??
+//    data class Fn(val argTypes: List<ArgsDeclaration.Item>, val retType: TypeDecl) : TypeDecl()
+    object TypeAny : TypeDecl()
+    object TypeNullableAny : TypeDecl(true)
+
+    class Simple(val name: String,isNullable: Boolean) : TypeDecl(isNullable)
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Visibility.kt

@@ -0,0 +1,8 @@
+package net.sergeych.lyng
+
+enum class Visibility {
+    Public, Private, Protected;//, Internal
+    val isPublic by lazy { this == Public }
+    @Suppress("unused")
+    val isProtected by lazy { this == Protected }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/globals.kt

@@ -0,0 +1,4 @@
+package net.sergeych.lyng
+
+
+val LyngVersion = BuildKonfig.version

lynglib/src/commonTest/kotlin/TypesTest.kt

@@ -0,0 +1,53 @@
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.eval
+import kotlin.test.Test
+
+class TypesTest {
+
+    @Test
+    fun testTypeCollection1() = runTest {
+        eval("""
+           class Point(x: Real, y: Real)
+           assert(Point(1,2).x == 1)
+           assert(Point(1,2).y == 2)
+           assert(Point(1,2) is Point)
+        """.trimIndent())
+
+    }
+    @Test
+    fun testTypeCollection2() = runTest {
+        eval("""
+           fun fn1(x: Real, y: Real): Real { x + y }
+        """.trimIndent())
+
+    }
+    @Test
+    fun testTypeCollection3() = runTest {
+        eval("""
+           class Test(a: Int) {
+              fun fn1(x: Real, y: Real): Real { x + y }
+           }
+        """.trimIndent())
+    }
+
+    @Test
+    fun testExternDeclarations() = runTest {
+        eval("""
+            extern fun foo1(a: String): Void
+            assertThrows { foo1("1") }
+           class Test(a: Int) {
+              extern fun fn1(x: Real, y: Real): Real
+//              extern val b: Int
+           }
+//           println("1")
+           val t = Test(0)
+//           println(t.b)
+//           println("2")
+           assertThrows {
+            t.fn1(1,2)
+           }
+//           println("4")
+           
+        """.trimIndent())
+    }
+}

lynglib/src/jvmTest/kotlin/BookTest.kt

@@ -255,6 +255,16 @@ class BookTest {
         runDocTests("../docs/Range.md")
     }
 
+    @Test
+    fun testSet() = runTest {
+        runDocTests("../docs/Set.md")
+    }
+
+    @Test
+    fun testMap() = runTest {
+        runDocTests("../docs/Map.md")
+    }
+
     @Test
     fun testSampleBooks() = runTest {
         for (bt in Files.list(Paths.get("../docs/samples")).toList()) {
@@ -268,4 +278,9 @@ class BookTest {
     fun testArgumentBooks() = runTest {
         runDocTests("../docs/declaring_arguments.md")
     }
+
+    @Test
+    fun testExceptionsBooks() = runTest {
+        runDocTests("../docs/exceptions_handling.md")
+    }
 }

settings.gradle.kts

@@ -18,5 +18,5 @@ dependencyResolutionManagement {
 }
 
 rootProject.name = "lyng"
-include(":library")
+include(":lynglib")
 include(":lyng")