README.md

purescript-wasm

A PureScript library containing syntax definitions and encoders for WebAssembly. You can use this to generate Wasm for your own compiler projects. This library does not compile PureScript to Wasm.

Minimal example

As a small example we'll define a module with a main function that takes no arguments and returns an i32. It'll add the numbers 20 and 22 and return 42 as its result. I'll include a bit of FFI to instantiate and run the generated Wasm.

module Main where

import Prelude

import Data.ArrayBuffer.Types (Uint8Array)
import Effect (Effect)
import Wasm.Encode as Encode
import Wasm.Syntax as S

foreign import execWasm :: Uint8Array -> Effect Unit

wasmModule :: S.Module
wasmModule = S.emptyModule
  { types = [ { arguments: [], results: [ S.NumType S.I32 ] } ]
  , funcs = [ { locals: [], type: 0, body: [ S.I32Const 20, S.I32Const 22, S.I32Add ] } ]
  , exports = [ { name: "main", desc: S.ExportFunc 0 } ]
  }

main :: Effect Unit
main = do
  let bytes = Encode.encodeModule wasmModule
  execWasm bytes

export const execWasm = (bytes) => () => {
  WebAssembly.instantiate(bytes, {})
    .then(module => console.log(module.instance.exports.main()))
}

For a real compiler project you'll likely want to define your own builder on top of Wasm.Syntax to keep track of indices for you. An example of this can be seen in example/src/WasmBuilder.purs.