tonyyuyiding/asdl

Generate AST types from ASDL (Abstract Syntax Description Language) descriptions.

This project is under development. We will try to keep the API stable, but breaking changes might still occur in some cases.

Usage

CLI

moon run cmd/asdl-gen path/to/schema.asdl --target moonbit -o schema.mbt

Omit -o to print to stdout. Use --target to specify target language (default: moonbit).

Only the MoonBit backend is available currently. Additional language emitters have been planned.

Library

///|
test "asdl_to_moonbit" {
  let asdl =
    #|module Expr {
    #|    expr = Num(int n) | Add(expr left, expr right)
    #|}
  let code = @asdl.asdl_to_moonbit(asdl)
  let expected =
    #|///|
    #|pub type Identifier = StringView
    #|
    #|///|
    #|pub(all) enum Expr {
    #|  Num(n~ : Int)
    #|  Add(left~ : Expr, right~ : Expr)
    #|} derive(Debug)
    #|
    #|///|
    #|pub extend Expr with Debug::{ to_repr }
    #|
  assert_eq(code, expected)
}

Pipeline

Stage	Package	Role
Lexer	lexer/	Tokenize ASDL source
Parser	parser/	Build an ASDL module AST
Checker	checker/	Validate type names and definitions
Backend	backend/	Emit target-language source (MoonBit today)

The root package re-exports these stages and provides asdl_to_moonbit as a single entry point: tokenize → parse → check → emit.

Bootstrapping

ASDL can describe itself. parser/asdl.asdl is a meta-schema for ASDL modules, definitions, constructors, and fields:

module ASDL {
    module = (identifier name, definition* definitions)

    definition = Product(identifier name, field* fields)
               | Sum(identifier name, constructor* constructors, field* attributes)

    constructor = (identifier name, field* fields)

    field = (identifier type, quantifier? quant, identifier? name)

    quantifier = Optional | Sequence
}

Feeding this file through the generator produces parser/ast.mbt — the MoonBit types being used by the parser :D