ccorcos

// A Stream is an abstraction over strings and arrays so that we don't have to
// keep chopping them up everywhere eating up CPU. An iterable is either a
// string or an array. The cursor is an index that marks the beginning of the
// stream and the length is the amount left in the Stream.
export class Stream {
  constructor(iterable, cursor, length) {
    this.iterable = iterable
    this.cursor = cursor || 0
    this.length = length === undefined
                ? iterable.length - this.cursor

ccorcos

const char = c => input => {
  if (input[0] === c) {
    return {success: true, rest: input.slice(1)}
  }
  return {success: false, rest: input}
}
char('a')('abc') 
// => { success: true, rest: 'bc' }

ccorcos

const sequence = parsers => input => {
  let next = input
  for (var i = 0; i < parsers.length; i++) {
    const parser = parsers[i]
    const {success, rest} = parser(next)
    if (!success) {
      return {success, rest}
    }
    next = rest
  }

ccorcos

const string = str => sequence(str.split('').map(char))
string('abc')('abcdefg')
// => { success: true, rest: 'defg' }

ccorcos

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}
}

ccorcos

class Stream {
  constructor(iterable, cursor, length) {
    this.iterable = iterable
    this.cursor = cursor || 0
    this.length = length === undefined
      ? iterable.length - this.cursor
      : length
  }
  // Get the first value from the iterable.
  head() {

ccorcos

class Result {
  constructor(value, rest) {
    this.value = value
    this.rest = rest
  }
}

class Success extends Result {
  map(fn) {
    return new Success(fn(this.value), this.rest)

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))
    }

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

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)