Walt Plugin Closures

This is a reference implementation of Closures plugin for the Walt WebAssembly Compiler.

Syntax

type Func = () => i32;
// New GenericType "Lambda"
type Closure = Lambda;

// Closures require a table, because closure calls are indirect_call
const table: Table = { initial: 1, element: 'anyfunc' };

function getClosure(): Closure {
  const x: i32 = 0;
  // Closures can be defined with arrow function syntax
  return (): i32 => {
    x += 1;
    return x;
  };
}

export function run(): i32 {
  const closure: Closure = getClosure();
  closure();
  closure();
  return closure(); // 3
}

Install

npm install walt-plugin-syntax-closure

API

import { compile } from 'walt-compiler';
import { plugin, imports } from 'walt-plugin-syntax-closure';

// .walt source with closures
const source = `...`;

// compiler options
const options = {
  extensions: [plugin],
};

// Closures require an additional import for support. It's provided by the plugin
Promise.resolve(imports(options, compile))
  .then(closureImports =>
    WebAssembly.instantiate(compile(source, options).buffer(), closureImports)
  )
  .then(mod => mod.instance.exports.run());

CLI

N/A

Reference

This plugin is meant to act as a reference example of plugins for the Walt compiler. To demonstrate this it extends the grammar(syntax), the semantic parser as well as provides a "side-module" import for it's run-time features.

Grammar

The plugin adds an additional Node type Closure and makes it a valid Expression type. For the full grammar see the Grammar File.

Semantic Parser

This plugin extends the semantic parser by parsing the new syntax down to the supported AST format of the core compiler. See the main plugin source for how the semantic parser is extended.

Imports

Ths plugin provides a run-time import for closure support. The following header is added to every module using closures.

// Start Closure Imports Header
import {
  __closure_malloc: ClosureGeti32,
  __closure_free: ClosureFree,
  __closure_get_i32: ClosureGeti32,
  __closure_get_f32: ClosureGetf32,
  __closure_get_i64: ClosureGeti64,
  __closure_get_f64: ClosureGetf64,
  __closure_set_i32: ClosureSeti32,
  __closure_set_f32: ClosureSetf32,
  __closure_set_i64: ClosureSeti64,
  __closure_set_f64: ClosureSetf64
} from 'walt-plugin-closure';
type ClosureFree = (i32) => void;
type ClosureGeti32 = (i32) => i32;
type ClosureGetf32 = (i32) => f32;
type ClosureGeti64 = (i32) => i64;
type ClosureGetf64 = (i32) => f64; type ClosureSeti32 = (i32, i32) => void;
type ClosureSetf32 = (i32, f32) => void;
type ClosureSeti64 = (i32, i64) => void;
type ClosureSetf64 = (i32, f64) => void;
// End Closure Imports Header

Note: There is no memory cleanup in the reference implementation of the imports.

Note: You may provide your own import object under walt-plugin-closure as long as it matches the API above. The buit-in import provided by plugin isn't required.