choice

choice combinator tries to apply ps parsers in order, until one of them succeeds. Returns a value of the succeeding parser. A committed failure stops it right there and is reported as is, not as the failure that got the furthest. Anything a discarded alternative recovered is dropped along with that alternative.

Usage

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

Success

run(Parser).with('true')

{
  isOk: true,
  start: 0,
  end: 4,
  pos: 4,
  value: 'true'
}

If all parsers fail, the failure that progressed furthest into the input is reported; on a tie, the first one wins.

Failure

run(Parser).with('yank')

{
  isOk: false,
  start: 0,
  end: 4,
  pos: 0,
  expected: 'true'
}

---

run(Parser).with('maybe')

{
  isOk: false,
  start: 0,
  end: 4,
  pos: 0,
  expected: 'true'
}