raganwald

// See: http://raganwald.com/2019/02/27/enumerability.html

// combinators

function slice (generator, n, limit = Infinity) {
  return function * sliced () {
    let i = 0;
    
    for (const element of generator()) {
      if (i++ < n) continue;

raganwald

// Inspired by:
//
// "Eh, have another semi-periodic reminder that ()() is not a palindrome but ())( is"
//
// --https://twitter.com/_julesh_/status/1101262745092218882

const END = Symbol('end');

class PushdownAutomaton {
  constructor(internal = 'start', external = []) {

raganwald

// memoizes ordinary functions
const memoized = (fn, keymaker = JSON.stringify) => {
  const lookupTable = new Map();

  return function (...args) {
    const key = keymaker.call(this, args);

    return lookupTable[key] || (lookupTable[key] = fn.apply(this, args));
  }
};

raganwald

// The Deterministic Pushdown Automata Engine

const END = Symbol('end');
const RECOGNIZED = Symbol('recognized');
const UNRECOGNIZED = Symbol('unrecognized');
const POP = Symbol('pop');

function DPA (start) {
  return string => {
    const stack = [];

raganwald

function balanced (string) {
  const iterator = string[Symbol.iterator]();
  
  return balancedIterator(iterator) === true;
}

const CLOSE = {
  '(': ')',
  '[': ']',
  '{': '}'

raganwald

const just =
  target =>
    input =>
      input.startsWith(target) &&
      target;

const cases =
  (...patterns) =>
    input => {
      const matches = patterns.map(p => p(input)).filter(m => m !== false);

raganwald

//
// http://raganwald.com/2019/01/14/structural-sharing-and-copy-on-write.html
// http://raganwald.com/2019/01/26/reduce-reuse-recycle.html
//

const SliceHandler = {
  has (slice, property) {
    if (property in slice) {
      return true;
    }

raganwald

const ComposableCarCdr = {
  has (target, name) {
    if (name in target) {
      return true;
    }
    
    if (name === Symbol.isConcatSpreadable) {
      return true;
    }
    

raganwald

function scoop(before, fromPit) {
  const after = before.slice(0);
  const seedsInHand = after[fromPit];
  
  after[fromPit] = 0;
  
  return [after, seedsInHand];
}

function nextPit(pit) {

raganwald

function isBalancedSimple (before) {
  if (before === '') return true;
  
  const after = before.replace('()','');
  
  return (before !== after) && isBalancedSimple(after);
}

function isBalancedMultiple (before) {
  if (before === '') return true;