choice primitive ​

Signature ​

function choice<T extends Array<Parser<unknown>>>(...ps: T): Parser<ToUnion<T>>
function choice<T>(...ps: Array<Parser<T>>): Parser<T>

Description ​

choice combinator tries to apply ps parsers in order, until one of them succeeds. Returns a value of the succeeding parser.

Usage ​

const Parser = choice(
  string('true'),
  string('false')
)

run(Parser).with('true')

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

Notice how the expected field differs depending on the input, specifically its length.

run(Parser).with('yank')

{
  isOk: false,
  span: [ 0, 4 ],
  pos: 0,
  expected: 'true'
}

run(Parser).with('maybe')

{
  isOk: false,
  span: [ 0, 5 ],
  pos: 0,
  expected: 'false'
}