lys







Lys, a language that compiles to WebAssembly.

Read more about it in this blog post.

Where to start?

Getting started

For the time being I’ll use npm to distribute the language.

  1. npm i -g lys-compiler
  2. Create a folder and a file main.lys

    import support::env
    
    #[export]
    fun test(): void = {
      support::test::START("This is a test suite")
    
      printf("Hello %X", 0xDEADBEEF)
      support::test::mustEqual(3 as u8, 3 as u16, "assertion name")
    
      support::test::END()
    }
    
  3. Run lys-compiler main.lys --test --wast. It will create main.wasm main.wast and will run the exported function named test.

How does it look?

Structs & Implementing operators

struct Vector3(x: f32, y: f32, z: f32)

impl Vector3 {
  fun -(lhs: Vector3, rhs: Vector3): Vector3 =
    Vector3(
      lhs.x - rhs.x,
      lhs.y - rhs.y,
      lhs.z - rhs.z
    )

  fun property_length(this: Vector3): f32 =
    f32.sqrt(
      this.x * this.x +
      this.y * this.y +
      this.z * this.z
    )
}

fun distance(from: Vector3, to: Vector3): f32 = {
  (from - to).length
}

Pattern matching

// this snippet is an actual unit test

import support::test

enum Color {
  Red
  Green
  Blue
  Custom(r: i32, g: i32, b: i32)
}

fun isRed(color: Color): boolean = {
  match color {
    case is Red -> true
    case is Custom(r, g, b) -> r == 255 && g == 0 && b == 0
    else -> false
  }
}

#[export]
fun main(): void = {
  mustEqual(isRed(Red), true, "isRed(Red)")
  mustEqual(isRed(Green), false, "isRed(Green)")
  mustEqual(isRed(Blue), false, "isRed(Blue)")

  mustEqual(isRed(Custom(255,0,0)), true, "isRed(Custom(255,0,0))")
  mustEqual(isRed(Custom(0,1,3)), false, "isRed(Custom(0,1,3))")
  mustEqual(isRed(Custom(255,1,3)), false, "isRed(Custom(255,1,3))")
}

Algebraic data types

// this snippet is an actual unit test

enum Tree {
  Node(value: i32, left: Tree, right: Tree)
  Empty
}

fun sum(arg: Tree): i32 = {
  match arg {
    case is Empty -> 0
    case is Node(value, left, right) -> value + sum(left) + sum(right)
  }
}

#[export]
fun main(): void = {
  val tree = Node(42, Node(3, Empty, Empty), Empty)

  support::test::mustEqual(sum(tree), 45, "sum(tree) returns 45")
}

Types and overloads are created in the language itself

The compiler only knows how to emit functions and how to link function names. I did that so I had fewer things hardcoded into the compiler and allows me to write the language in the language.

To do that, I had to add either a %wasm { ... } code block, and a %stack { ... } type.

/** We first define the type `int` */
type int = %stack { wasm="i32", size=4 }

/** Implement some operators for the type `int` */
impl int {
  fun +(lhs: int, rhs: int): int = %wasm {
    (i32.add (get_local $lhs) (get_local $rhs))
  }
  fun -(lhs: int, rhs: int): int = %wasm {
    (i32.sub (get_local $lhs) (get_local $rhs))
  }
  fun >(lhs: int, rhs: int): boolean = %wasm {
    (i32.gt_s (get_local $lhs) (get_local $rhs))
  }
}

fun fibo(n: int, x1: int, x2: int): int = {
  if (n > 0) {
    fibo(n - 1, x2, x1 + x2)
  } else {
    x1
  }
}

#[export "fibonacci"] // "fibonacci" is the name of the exported function
fun fib(n: int): int = fibo(n, 0, 1)

Some sugar

Enum types

enum Tree {
  Node(value: i32, left: Tree, right: Tree)
  Empty
}

Is the sugar syntax for

type Tree = Node | Empty

struct Node(value: i32, left: Tree, right: Tree)
struct Empty()

impl Tree {
  fun is(lhs: Tree): boolean = lhs is Node || lhs is Empty
  // ...
}

impl Node {
  fun as(lhs: Node): Tree = %wasm { (local.get $lhs) }

  // ... many methods were removed for clarity ..
}

impl Empty {
  fun as(lhs: Node): Tree = %wasm { (local.get $lhs) }
  // ...
}

is and as operators are just functions

impl u8 {
  /**
   * Given an expression with the shape:
   *
   *   something as Type
   *   ^^^^^^^^^    ^^^^
   *        $lhs    $rhs
   *
   * A function with the signature:
   *     fun as($lhs: LHSType): $rhs = ???
   *
   * Will be searched in the impl of LHSType
   *
   */


  fun as(lhs: u8): f32 = %wasm { (f32.convert_i32_u (get_local $lhs)) }
}

fun byteAsFloat(value: u8): f32 = value as f32
struct CustomColor(rgb: i32)

type Red = void
impl Red {
  fun is(lhs: CustomColor): boolean = match lhs {
    case is Custom(rgb) -> (rgb & 0xFF0000) == 0xFF0000
    else -> false
  }
}

var x = CustomColor(0xFF0000) is Red

// this may not be a good thing, but you get the idea

There are no dragons behind the structs

The struct keyword is only a high level construct that creats a type and base implementation of something that behaves like a data type, normally in the heap.

struct Node(value: i32, left: Tree, right: Tree)

Is the sugar syntax for

// We need to keep the name and order of the fields for deconstructors

type Node = %struct { value, left, right }

impl Node {
  fun as(lhs: Node): Tree = %wasm {
    (local.get $lhs)
  }

  #[explicit]
  fun as(lhs: Node): ref = %wasm {
    (local.get $lhs)
  }

  // the discriminant is the type number assigned by the compiler
  #[inline]
  private fun Node$discriminant(): u64 = {
    val discriminant: u32 = Node.^discriminant
    discriminant as u64 << 32
  }

  // this is the function that gets called when Node is used as a function call
  fun apply(value: i32, left: Tree, right: Tree): Node = {
    // a pointer is allocated. Then using the function `fromPointer` it is converted
    // to a valid Node reference
    var $ref = fromPointer(system::memory::calloc(1 as u32, Node.^allocationSize))
    property$0($ref, value)
    property$1($ref, left)
    property$2($ref, right)
    $ref
  }

  // this function converts a raw address into a valid Node type
  private fun fromPointer(ptr: u32): Node = %wasm {
    (i64.or (call Node$discriminant) (i64.extend_u/i32 (local.get $ptr)))
  }

  fun ==(a: Node, b: Node): boolean = %wasm {
    (i64.eq (local.get $a) (local.get $b))
  }

  fun !=(a: Node, b: Node): boolean = %wasm {
    (i64.ne (local.get $a) (local.get $b))
  }

  fun property_value(self: Node): i32 = property$0(self)
  fun property_value(self: Node, value: i32): void = property$0(self, value)

  #[inline]
  private fun property$0(self: Node): i32 = i32.load(self, Node.^property$0_offset)
  #[inline]
  private fun property$0(self: Node, value: i32): void = i32.store(self, value, Node.^property$0_offset)

  fun property_left(self: Node): Tree = property$1(self)
  fun property_left(self: Node, value: Tree): void = property$1(self, value)

  #[inline]
  private fun property$1(self: Node): Tree = Tree.load(self, Node.^property$1_offset)
  #[inline]
  private fun property$1(self: Node, value: Tree): void = Tree.store(self, value, Node.^property$1_offset)

  fun property_right(self: Node): Tree = property$2(self)
  fun property_right(self: Node, value: Tree): void = property$2(self, value)

  #[inline]
  private fun property$2(self: Node): Tree = Tree.load(self, Node.^property$2_offset)
  #[inline]
  private fun property$2(self: Node, value: Tree): void = Tree.store(self, value, Node.^property$2_offset)

  fun is(a: (Node | ref)): boolean = %wasm {
    (i64.eq (i64.and (i64.const 0xffffffff00000000) (local.get $a)) (call Node$discriminant))
  }

  fun store(lhs: ref, rhs: Node, offset: u32): void = %wasm {
    (i64.store (i32.add (local.get $offset) (call addressFromRef (local.get $lhs))) (local.get $rhs))
  }

  fun load(lhs: ref, offset: u32): Node = %wasm {
    (i64.load (i32.add (local.get $offset) (call addressFromRef (local.get $lhs))))
  }
}

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