11 KiB
Ling tutorial
Ling is a very simple language, where we take only most important and popular features from other scripts and languages. In particular, we adopt principle of minimal confusion[^1]. In other word, the code usually works as expected when you see it. So, nothing unusual.
Expressions
Everything is an expression in Ling. Even an empty block:
// empty block
>>> void
any block also returns it's last expression:
if( true ) {
2 + 2
3 + 3
}
>>> 6
If you don't want block to return anything, use void:
fn voidFunction() {
3 + 4 // this will be ignored
void
}
voidFunction()
>>> void
otherwise, last expression will be returned:
fn normalize(value, minValue, maxValue) {
(value - minValue) / (maxValue-minValue)
}
normalize( 4, 0.0, 10.0)
>>> 0.4
Every construction is an expression that returns something (or void):
val x = 111 // or autotest will fail!
val limited = if( x > 100 ) 100 else x
limited
>>> 100
You can use blocks in if statement, as expected:
val x = 200
val limited = if( x > 100 ) {
100 + x * 0.1
}
else
x
limited
>>> 120.0
When putting multiple statments in the same line it is convenient and recommended to use ;:
var from; var to
from = 0; to = 100
>>> 100
Notice: returned value is 100 as assignment operator returns its assigned value.
Most often you can omit ;, but improves readability and prevent some hardly seen bugs.
Assignments
Assignemnt is an expression that changes its lvalue and return assigned value:
var x = 100
x = 20
println(5 + (x=6)) // 11: x changes its value!
x
>>> 11
>>> 6
As the assignment itself is an expression, you can use it in strange ways. Just remember to use parentheses as assignment operation insofar is left-associated and will not allow chained assignments (we might fix it later). Use parentheses insofar:
var x = 0
var y = 0
x = (y = 5)
assert(x==5)
assert(y==5)
>>> void
Note that assignment operator returns rvalue, it can't be assigned.
Modifying arithmetics
There is a set of assigning operations: +=, -=, *=, /= and even %=.
var x = 5
assert( 25 == (x*=5) )
assert( 25 == x)
assert( 24 == (x-=1) )
assert( 12 == (x/=2) )
x
>>> 12
Notice the parentheses here: the assignment has low priority!
These operators return rvalue, unmodifiable.
Assignemnt return r-value!
Math
It is rather simple, like everywhere else:
val x = 2.0
sin(x * π/4) / 2.0
>>> 0.5
See math for more on it. Notice using Greek as identifier, all languages are allowed.
Logical operation could be used the same
var x = 10
++x >= 11
>>> true
Supported operators
| op | ass | args |
|---|---|---|
| + | += | Int or Real |
| - | -= | Int or Real |
| * | *= | Int or Real |
| / | /= | Int or Real |
| % | %= | Int or Real |
| && | Bool | |
| || | Bool | |
| !x | Bool | |
| < | String, Int, Real | |
| <= | String, Int, Real | |
| >= | String, Int, Real | |
| > | String, Int, Real | |
| == | Any | |
| != | Any | |
| ++a, a++ | Int | |
| --a, a-- | Int |
Variables
Much like in kotlin, there are variables:
var name = "Sergey"
Variables can be not initialized at declaration, in which case they must be assigned before use, or an exception will be thrown:
var foo
// WRONG! Exception will be thrown at next line:
foo + "bar"
Correct pattern is:
foo = "foo"
// now is OK:
foo + bar
This is though a rare case when you need uninitialized variables, most often you can use conditional operators and even loops to assign results (see below).
Constants
Almost the same, using val:
val foo = 1
foo += 1 // this will throw exception
Constants
Same as in kotlin:
val HalfPi = π / 2
Note using greek characters in identifiers! All letters allowed, but remember who might try to read your script, most likely will know some English, the rest is the pure uncertainty.
Defining functions
fun check(amount) {
if( amount > 100 )
"enough"
else
"more"
}
>>> Callable@...
Notice how function definition return a value, instance of Callable.
You can use both fn and fun. Note that function declaration is an expression returning callable.
There are default parameters in Ling:
fn check(amount, prefix = "answer: ") {
prefix + if( amount > 100 )
"enough"
else
"more"
}
assert( "do: more" == check(10, "do: ") )
check(120)
>>> answer: enough
Closures
Each block has an isolated context that can be accessed from closures. For example:
var counter = 1
// this is ok: coumter is incremented
fun increment(amount=1) {
// use counter from a closure:
counter = counter + amount
}
val taskAlias = fun someTask() {
// this obscures global outer var with a local one
var counter = 0
// ...
counter = 1
// ...
counter
}
>>> void
As was told, fun statement return callable for the function, it could be used as a parameter, or elsewhere
to call it:
val taskAlias = fun someTask() {
println("Hello")
}
// call the callable stored in the var
taskAlias()
// or directly:
someTask()
>>> Hello
>>> Hello
>>> void
If you need to create unnamed function, use alternative syntax (TBD, like { -> } ?)
Flow control operators
if-then-else
As everywhere else, and as expression:
val count = 11
if( count > 10 )
println("too much")
else {
// do something else
println("just "+count)
}
>>> too much
>>> void
Notice returned value void: it is because of println have no return value, e.g., void.
Or, more neat:
var count = 3
println( if( count > 10 ) "too much" else "just " + count )
>>> just 3
>>> void
while
Regular pre-condition while loop, as expression, loop returns it's last line result:
var count = 0
while( count < 5 ) {
count++
count * 10
}
>>> 50
We can break as usual:
var count = 0
while( count < 5 ) {
if( count < 5 ) break
count = ++count * 10
}
>>> void
Why void? Because break drops out without the chute, not providing anything to return. Indeed, we should provide
exit value in the case:
var count = 0
while( count < 50 ) {
if( count > 3 ) break "too much"
count = ++count * 10
"wrong "+count
}
>>> too much
Breaking nested loops
If you have several loops and want to exit not the inner one, use labels:
var count = 0
// notice the label:
outerLoop@ while( count < 5 ) {
var innerCount = 0
while( innerCount < 100 ) {
innerCount = innerCount + 1
if( innerCount == 5 && count == 2 )
// and here we break the labelled loop:
break@outerLoop "5/2 situation"
}
count = count + 1
count * 10
}
>>> 5/2 situation
and continue
We can skip the rest of the loop and restart it, as usual, with continue operator.
var count = 0
var countEven = 0
while( count < 10 ) {
count = count + 1
if( count % 2 == 1) continue
countEven = countEven + 1
}
"found even numbers: " + countEven
>>> found even numbers: 5
continue can't "return" anything: it just restarts the loop. It can use labeled loops to restart outer ones:
var count = 0
var total = 0
// notice the label:
outerLoop@ while( count < 5 ) {
count = count + 1
var innerCount = 0
while( innerCount < 10 ) {
innerCount = innerCount + 1
if( innerCount == 10 )
continue@outerLoop
}
// we don't reach it because continue above restarts our loop
total = total + 1
}
total
>>> 0
Notice that total remains 0 as the end of the outerLoop@ is not reachable: continue is always called and always make
Ling to skip it.
Labels@
The label can be any valid identifier, even a keyword, labels exist in their own, isolated world, so no risk of occasional clash. Labels are also scoped to their context and do not exist outside it.
Right now labels are implemented only for the while loop. It is intended to be implemented for all loops and returns.
Self-assignments in expression
There are auto-increments and auto-decrements:
var counter = 0
assert(counter++ * 100 == 0)
assert(counter == 1)
>>> void
but:
var counter = 0
assert( ++counter * 100 == 100)
assert(counter == 1)
>>> void
The same with --:
var count = 100
var sum = 0
while( count > 0 ) sum = sum + count--
sum
>>> 5050
There are self-assigning version for operators too:
var count = 100
var sum = 0
while( count > 0 ) sum += count--
sum
>>> 5050
Comments
// single line comment
var result = null // here we will store the result
>>> void
Integral data types
| type | description | literal samples |
|---|---|---|
| Int | 64 bit signed | 1 -22 0x1FF |
| Real | 64 bit double | 1.0, 2e-11 |
| Bool | boolean | true false |
| String | unicode string, no limits | "hello" (see below) |
| Void | no value could exist, singleton | void |
| Null | missing value, singleton | null |
| Fn | callable type |
See also math operations
String details
String operations
Concatenation is a +: "hello " + name works as expected. No confusion.
Literals
String literal could be multiline:
"Hello
World"
though multiline literals is yet work in progress.
Built-in functions
See math functions, and:
| name | description |
|---|---|
| assert(condition,message="assertion failed") | runtime code check. There will be an option to skip them |