map

map combinator applies fn to the parser's result and returns the result of that fn. fn also receives the result's span as its second argument.

Usage

function add([left, right]: [number, number]): number {
  return left + right
}

const Parser = map(
  outer(whole(), string('+'), whole()),
  add
)

Success

run(Parser).with('2+2')

{
  isOk: true,
  start: 0,
  end: 3,
  pos: 3,
  value: 4
}

Failure

run(Parser).with('2-2')

{
  isOk: false,
  start: 1,
  end: 2,
  pos: 1,
  expected: '+'
}