grammar ​

Description ​

grammar is used to create a self-contained grammar.

Similarly to defer, this allows for the creation of mutually recursive parsers, but lets you define all of the component parsers within a single call.

The function takes an object with parser initializers, and returns an object with all of those parsers initialized. Within the parser initializers, use this to reference other initialized parsers, as in the example below.

The properties of the resulting object are just regular parsers - you can freely destructure these, pass them around individually, or compose them with other grammars, parsers or combinators as needed.

Usage ​

Here is an example of a simple grammar that recursively matches ab sequences:

const ab = grammar({
  a(): Parser<string> {
    return map(
      sequence(
        string('a'),
        optional(this.b)
      ),
      ([a, b]) => a + (b ?? '')
    )
  },
  b(): Parser<string> {
    return map(
      sequence(
        string('b'),
        choice(this.a, this.b)
      ),
      ([b, a]) => b + a
    )
  }
})

The individual properties are just regular parsers:

const { a } = ab

console.log(run(a).with('abba'))

{
  isOk: true,
  span: [0, 4],
  pos: 4,
  value: 'abba'
}