ReScript Parser

@resinfo/parser is a parser combinator library for ReScript.

Note:

Please be aware that this is considered alpha quality software. While there is a test suite that includes a JSON parser and a simple s-expression parser, you might want to write your own tests before using in production.

Installation

via NPM.

yarn add @resinfo/parser
# or
npm install --save @resinfo/parser

Usage

module P = Res_parser

// Define our AST
type sign = Plus | Subtract | Multiply
type number = SingleDigit(int)
type expression = Expression(number, sign, number)

// Parse sign and transform into AST node
type sign_ = P.t<sign>
let sign: sign_ = P.choice([
  P.char('+')->P.map(_ => Plus),
  P.char('-')->P.map(_ => Subtract),
  P.char('x')->P.map(_ => Multiply),
])

// Helper that returns any parser
// that's found to be wrapped in whitespace
type manyWhitespace = P.t<list<char>>
let manyWhitespace: manyWhitespace = P.many(P.char(' '))

// Parse single digit and transform into AST node
type singleDigit = P.t<number>
let singleDigit: singleDigit =
  P.satisfy(char => char >= '0' && char <= '9')
  ->P.map(Char.escaped)
  ->P.map(int_of_string)
  ->P.map(x => SingleDigit(x))
  ->P.between(manyWhitespace, manyWhitespace)

// Combine sign and digit parsers into fully typed AST.
type parser = P.t<expression>
let parser: parser =
  singleDigit
  ->P.andThen(sign)
  ->P.andThen(singleDigit)
  ->P.map((((left, sign), right)) => Expression(left, sign, right))

// Run our parser against an input string.
type result = result<(expression, string), string>
let result: result = P.run(parser, " 1 +  4  ")

// Result is a tuple of a valid AST and the state object.
result == Ok(Expression(SingleDigit(1), Plus, SingleDigit(4)), _)

Notes:

Inspired by (and essentially converted from) the excellent series and library by Scott Wlaschin, originally written in F#. This was itself inspired by the equally excellent (though slightly more esoteric) paper by Graham Hutton and Erik Meijer on Monadic Parsers (Haskell video).

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

License

MIT