parser4.js

const either = parsers => input => {
  for (var i = 0; i < parsers.length; i++) {
    const parser = parsers[i]
    const {success, rest} = parser(input)
    if (success) {
      return {success, rest}
    }
  }
  return {success: false, rest: input}
}
either([string('abc'), string('abab')])('abcd')
// => { success: true, rest: 'd' }
either([string('abc'), string('abab')])('ababab')
// => { success: true, rest: 'ab' }
either([string('abc'), string('abab')])('aba')
// => { success: false, rest: 'aba' }