hexlet-pairs/dist/index.js

## Install

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});

var _typeof = typeof Symbol === "function" && typeof Symbol.iterator === "symbol" ? function (obj) { return typeof obj; } : function (obj) { return obj && typeof Symbol === "function" && obj.constructor === Symbol && obj !== Symbol.prototype ? "symbol" : typeof obj; };

/**
 * Check if something is pair
 * @example
 * const pair = cons(5, 'hello');
 * isPair(pair); // true
 * isPair(5); // false
 **/
var isPair = exports.isPair = function isPair(pair) {
  return typeof pair === 'function' && pair.pair;
};

var checkPair = exports.checkPair = function checkPair(pair) {
  if (!isPair(pair)) {
    var value = (typeof pair === 'undefined' ? 'undefined' : _typeof(pair)) === 'object' ? JSON.stringify(pair, null, 2) : String(pair);
    throw new Error('Argument must be pair, but it was \'' + value + '\'');
  }
};

/**
 * Build pair
 * @example
 * const pair = cons(5, 'hello');
 * @example
 * const pair = cons(cons(1, null), 'world');
 **/
var cons = exports.cons = function cons(a, b) {
  var pair = function pair(message) {
    switch (message) {
      case 'car':
        return a;
      case 'cdr':
        return b;
      default:
        throw new Error('Unknown message \'' + message + '\'');
    }
  };
  pair.pair = true;
  return pair;
};

/**
 * Get car (first element) from pair
 * @example
 * const pair = cons(5, 'hello');
 * car(pair); // 5
 **/
var car = exports.car = function car(pair) {
  checkPair(pair);
  return pair('car');
};

/**
 * Get cdr (second element) from pair
 * @example
 * const pair = cons(5, 'hello');
 * cdr(pair); // hello
 **/
var cdr = exports.cdr = function cdr(pair) {
  checkPair(pair);
  return pair('cdr');
};

/**
 * Convert pair to string (recursively)
 * @example
 * toString(cons('', 10)); // ('', 10)
 **/
var toString = exports.toString = function toString(pair) {
  checkPair(pair);
  var rec = function rec(p) {
    if (!isPair(p)) {
      return String(p);
    }
    var left = car(p);
    var right = cdr(p);
    return '(' + rec(left) + ', ' + rec(right) + ')';
  };

  return rec(pair);
};

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