nothing

nothing simply resolves to null. It consumes no input and never fails, so it works as a default branch in combinators like choice, or as a placeholder to mapTo something else.

Usage

The example below reads an optional sign, defaulting to a positive one.

const Parser = choice(
  mapTo(string('-'), -1),
  mapTo(nothing(), 1)
)

Success

run(Parser).with('-')

{
  isOk: true,
  start: 0,
  end: 1,
  pos: 1,
  value: -1
}

Success

run(Parser).with('42')

{
  isOk: true,
  start: 0,
  end: 0,
  pos: 0,
  value: 1
}