ccorcos

const always = value => 
  new Parser(stream => new Success(value, stream))

const never = value => 
  new Parser(stream => new Failure(value, stream))

const append = (p1, p2) => 
  p1.chain(vs => p2.map(v => vs.concat([v])))

const concat = (p1, p2) =>

ccorcos

const either = list =>
  new Parser(stream => {
    for (let i = 0; i < list.length; i++) {
      const parser = list[i]
      const result = parser.run(stream)
      if (result instanceof Success) {
        return result
      }
    }
    return new Failure('either failed', stream)

ccorcos

char('a')
.chain(v1 => 
  char('b')
  .chain(v2 =>
    char('c')
    .map(v3 => [v1, v2, v3])
  )
)
.run('abc')
.fold(

ccorcos

char('a')
.chain(v => char('b'))
.chain(v => char('c'))
.run('abc')
.fold(
  v => console.log('success', v)
  e => console.log('error', e)
)
// => success c

ccorcos

char('a')
.bimap(
  v => v,
  e => 'character was not an a'
)
.run('b')
.fold(
  v => console.log('success', v)
  e => console.log('error', e)
)

ccorcos

char('a')
.map(v => v.toUpperCase())
.run('a')
.fold(
  v => console.log('success', v)
  e => console.log('error', e)
)
// => success A

ccorcos

char('a')
.run('a')
.fold(
  v => console.log('success', v)
  e => console.log('error', e)
)
// => success a

char('a')
.run('b')

ccorcos

const where = predicate =>
  new Parser(stream => {
    if (stream.length === 0) {
      return new Failure('unexpected end', stream)
    }
    const value = stream.head()
    if (predicate(value)) {
      return new Success(value, stream.move(1))
    }
    return new Failure('predicate did not match', stream)

ccorcos

const char = c =>
  new Parser(stream => {
    if (stream.length === 0) {
      return new Failure('unexpected end', stream))
    }
    const value = stream.head()
    if (value === c) {
      return new Success(value, stream.move(1))
    }
    return new Failure('char did not match', stream))

ccorcos

class Parser {
  constructor(parse) {
    this.parse = parse
  }
  run(iterable) {
    if (iterable instanceof Stream) {
      return this.parse(iterable)
    } else {
      return this.parse(new Stream(iterable))
    }