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var waltCompiler = require("walt-compiler")

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walt-compiler v0.21.0

Alternative syntax for WebAssembly text format

Walt Compiler

This is the main walt compiler package.


npm install --save walt-compiler


type Compile = (source: string, options?: Options) => Result

Compile and run Walt code in browser:

import { compile } from 'walt-compiler';

const buffer = compile(`
  let counter: i32 = 0;
  export function count(): i32 {
    counter += 1;
    return counter;

WebAssembly.instantiate(buffer).then(result => {
  console.log(`First invocation: ${result.instance.exports.count()}`);
  console.log(`Second invocation: ${result.instance.exports.count()}`);

Compile and save a .wasm file via Node.js:

const { compile } = require('walt-compiler');
const fs = require('fs');

const buffer = compile(`
  let counter: i32 = 0;
  export function count(): i32 {
    counter += 1;
    return counter;

fs.writeFileSync('bin.wasm', new Uint8Array(buffer));


type Result = {
  buffer: () => ArrayBuffer,
  ast: NodeType,
  semanticAST: NodeType


Unique (across function calls) ArrayBuffer instance.


The Program root node containing the source program without any type information. This is the node passed to semantic parser.


The Program root node containing the source program including the final type information. This is the AST version used to generate the final binary.


type Options = {
  version?: number,
  encodeNames?: boolean,
  filename?: string,
  extensions: Array<Plugin>


The target WebAssembly Standard (not to be confused with compiler version) version to which the source should be compiled to. Currently supported versions: 0x01


Whether or not names section should be encoded into the binary output. This enables a certain level of extra debug output in supported browser DevTools. Increases the size of the final binary. Default: false


Filename of the compiled source code. Used in error outputs. Default: unknown.walt


An array of functions which are compiler extensions. See the Plugin section for plugin details. Default: []

note: Plugins are applied from right to left with the core language features applied last.


The compiler may be extended via extensions or plugins. Each plugin must be a function return an object with the following keys: semantics, grammar. Where each value is a function.

type Plugin = (Options) => {
  semantics: ({ parser: Function, fragment: Function }) => {
    [string]: next => ([node: NodeType, context]) => NodeType
  grammar: Function

Each plugin is capable of editing the following features of the compiler:

  • grammar - The syntax or grammar which is considered valid by the compiler. This enables features like new keywords for example.
  • semantics - The parsing of the ast. Each key in the object returned by this method is expected to be a middleware like parser function which may edit the node passed into it.

For an example of how plugins work see the full list of core language feature plugins.

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