fix #17 do-while loops

+mode string functions
+val/var cold be initialized with statement and return assigned values

docs/tutorial.md

@@ -554,16 +554,16 @@ Or, more neat:
 
 ## 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 ) {
@@ -682,6 +682,36 @@ 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
 
@@ -791,7 +821,7 @@ 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
 
@@ -837,10 +867,36 @@ Are the same as in string literals with little difference:
 
 ## String details
 
+Strings are much like Kotlin ones:
+
+    "Hello".length
+    >>> 5
+And supports growing set of kotlin-borrowed operations, see below, for example:
+
+    assertEquals("Hell", "Hello".dropLast(1))
+    >>> 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                               |
+| 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] |
+
+
+
+
+
 ### Literals
 
 String literal could be multiline:

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

@@ -710,6 +710,7 @@ class Compiler(
         "val" -> parseVarDeclaration(id.value, false, cc)
         "var" -> parseVarDeclaration(id.value, true, cc)
         "while" -> parseWhileStatement(cc)
+        "do" -> parseDoWhileStatement(cc)
         "for" -> parseForStatement(cc)
         "break" -> parseBreakStatement(id.pos, cc)
         "continue" -> parseContinueStatement(id.pos, cc)
@@ -944,6 +945,59 @@ 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
+                        }
+                    }
+                }
+            } 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)
@@ -1149,7 +1203,7 @@ 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)
@@ -1184,7 +1238,7 @@ 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 ->
@@ -1196,7 +1250,7 @@ class Compiler(
             val initValue = initialExpression?.execute(context)?.byValueCopy() ?: ObjNull
 
             context.addItem(name, mutable, initValue, visibility)
-            ObjVoid
+            initValue
         }
     }
 

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

@@ -134,6 +134,13 @@ internal class CompilerContext(val tokens: List<Token>) {
         return default
     }
 
+//    fun expectKeyword(vararg keyword: String): String {
+//        val t = next()
+//        if (t.type != Token.Type.ID && t.value !in keyword) {
+//            throw ScriptError(t.pos, "expected one of ${keyword.joinToString()}")
+//
+//    }
+
 //    data class ReturnScope(val needCatch: Boolean = false)
 
 //    private val

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

@@ -4,7 +4,8 @@ class Context(
     val parent: Context?,
     val args: Arguments = Arguments.EMPTY,
     var pos: Pos = Pos.builtIn,
-    val thisObj: Obj = ObjVoid
+    val thisObj: Obj = ObjVoid,
+    var skipContextCreation: Boolean = false,
 ) {
     constructor(
         args: Arguments = Arguments.EMPTY,

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

@@ -286,6 +286,8 @@ object ObjNull : Obj() {
     override fun equals(other: Any?): Boolean {
         return other is ObjNull || other == null
     }
+
+    override fun toString(): String = "null"
 }
 
 interface Numeric {

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

@@ -40,6 +40,32 @@ data class ObjString(val value: String) : Obj() {
             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()) }
         }
     }

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

@@ -17,7 +17,7 @@ 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 {

library/src/commonTest/kotlin/ScriptTest.kt

@@ -174,7 +174,7 @@ class ScriptTest {
     fun varsAndConstsTest() = runTest {
         val context = Context(pos = Pos.builtIn)
         assertEquals(
-            ObjVoid, context.eval(
+            ObjInt(3L), context.eval(
                 """
             val a = 17
             var b = 3
@@ -434,6 +434,16 @@ class ScriptTest {
 
     }
 
+    @Test
+    fun whileAssignTest() = runTest {
+        eval("""
+            var t = 0
+            val x = while( t < 5 ) { t++ }
+            // last returned value is 4 - when t was 5 body was not executed
+            assertEquals( 4, x )
+        """.trimIndent())
+    }
+
     @Test
     fun whileTest() = runTest {
         assertEquals(
@@ -1662,4 +1672,28 @@ class ScriptTest {
         """.trimIndent())
     }
 
+    @Test
+    fun doWhileSimpleTest() = runTest {
+        eval("""
+            var sum = 0
+            var x = do {
+                val s = sum
+                sum += 1
+            } while( s < 10 )
+            assertEquals(11, x)
+        """.trimIndent())
+    }
+
+    @Test
+    fun testFailDoWhileSample1() = runTest {
+        eval("""
+            fun readLine() { "done: result" }
+            val result = do {
+                val line = readLine()
+            } while( !line.startsWith("done:") )
+            assertEquals("result", result.drop(6))
+            result
+        """.trimIndent())
+    }
+
 }