function _isPlaceholder(a) {
  return a != null && typeof a === 'object' && a['@@functional/placeholder'] === true;
}

/**
 * Optimized internal one-arity curry function.
 *
 * @private
 * @category Function
 * @param {Function} fn The function to curry.
 * @return {Function} The curried function.
 */

function _curry1(fn) {
  return function f1(a) {
    if (arguments.length === 0 || _isPlaceholder(a)) {
      return f1;
    } else {
      return fn.apply(this, arguments);
    }
  };
}

/**
 * Optimized internal two-arity curry function.
 *
 * @private
 * @category Function
 * @param {Function} fn The function to curry.
 * @return {Function} The curried function.
 */

function _curry2(fn) {
  return function f2(a, b) {
    switch (arguments.length) {
      case 0:
        return f2;

      case 1:
        return _isPlaceholder(a) ? f2 : _curry1(function (_b) {
          return fn(a, _b);
        });

      default:
        return _isPlaceholder(a) && _isPlaceholder(b) ? f2 : _isPlaceholder(a) ? _curry1(function (_a) {
          return fn(_a, b);
        }) : _isPlaceholder(b) ? _curry1(function (_b) {
          return fn(a, _b);
        }) : fn(a, b);
    }
  };
}

function _arity(n, fn) {
  /* eslint-disable no-unused-vars */
  switch (n) {
    case 0:
      return function () {
        return fn.apply(this, arguments);
      };

    case 1:
      return function (a0) {
        return fn.apply(this, arguments);
      };

    case 2:
      return function (a0, a1) {
        return fn.apply(this, arguments);
      };

    case 3:
      return function (a0, a1, a2) {
        return fn.apply(this, arguments);
      };

    case 4:
      return function (a0, a1, a2, a3) {
        return fn.apply(this, arguments);
      };

    case 5:
      return function (a0, a1, a2, a3, a4) {
        return fn.apply(this, arguments);
      };

    case 6:
      return function (a0, a1, a2, a3, a4, a5) {
        return fn.apply(this, arguments);
      };

    case 7:
      return function (a0, a1, a2, a3, a4, a5, a6) {
        return fn.apply(this, arguments);
      };

    case 8:
      return function (a0, a1, a2, a3, a4, a5, a6, a7) {
        return fn.apply(this, arguments);
      };

    case 9:
      return function (a0, a1, a2, a3, a4, a5, a6, a7, a8) {
        return fn.apply(this, arguments);
      };

    case 10:
      return function (a0, a1, a2, a3, a4, a5, a6, a7, a8, a9) {
        return fn.apply(this, arguments);
      };

    default:
      throw new Error('First argument to _arity must be a non-negative integer no greater than ten');
  }
}

/**
 * Optimized internal three-arity curry function.
 *
 * @private
 * @category Function
 * @param {Function} fn The function to curry.
 * @return {Function} The curried function.
 */

function _curry3(fn) {
  return function f3(a, b, c) {
    switch (arguments.length) {
      case 0:
        return f3;

      case 1:
        return _isPlaceholder(a) ? f3 : _curry2(function (_b, _c) {
          return fn(a, _b, _c);
        });

      case 2:
        return _isPlaceholder(a) && _isPlaceholder(b) ? f3 : _isPlaceholder(a) ? _curry2(function (_a, _c) {
          return fn(_a, b, _c);
        }) : _isPlaceholder(b) ? _curry2(function (_b, _c) {
          return fn(a, _b, _c);
        }) : _curry1(function (_c) {
          return fn(a, b, _c);
        });

      default:
        return _isPlaceholder(a) && _isPlaceholder(b) && _isPlaceholder(c) ? f3 : _isPlaceholder(a) && _isPlaceholder(b) ? _curry2(function (_a, _b) {
          return fn(_a, _b, c);
        }) : _isPlaceholder(a) && _isPlaceholder(c) ? _curry2(function (_a, _c) {
          return fn(_a, b, _c);
        }) : _isPlaceholder(b) && _isPlaceholder(c) ? _curry2(function (_b, _c) {
          return fn(a, _b, _c);
        }) : _isPlaceholder(a) ? _curry1(function (_a) {
          return fn(_a, b, c);
        }) : _isPlaceholder(b) ? _curry1(function (_b) {
          return fn(a, _b, c);
        }) : _isPlaceholder(c) ? _curry1(function (_c) {
          return fn(a, b, _c);
        }) : fn(a, b, c);
    }
  };
}

/**
 * Tests whether or not an object is an array.
 *
 * @private
 * @param {*} val The object to test.
 * @return {Boolean} `true` if `val` is an array, `false` otherwise.
 * @example
 *
 *      _isArray([]); //=> true
 *      _isArray(null); //=> false
 *      _isArray({}); //=> false
 */
var _isArray = Array.isArray || function _isArray(val) {
  return val != null && val.length >= 0 && Object.prototype.toString.call(val) === '[object Array]';
};

function _isString(x) {
  return Object.prototype.toString.call(x) === '[object String]';
}

/**
 * Tests whether or not an object is similar to an array.
 *
 * @private
 * @category Type
 * @category List
 * @sig * -> Boolean
 * @param {*} x The object to test.
 * @return {Boolean} `true` if `x` has a numeric length property and extreme indices defined; `false` otherwise.
 * @example
 *
 *      _isArrayLike([]); //=> true
 *      _isArrayLike(true); //=> false
 *      _isArrayLike({}); //=> false
 *      _isArrayLike({length: 10}); //=> false
 *      _isArrayLike({0: 'zero', 9: 'nine', length: 10}); //=> true
 *      _isArrayLike({nodeType: 1, length: 1}) // => false
 */

var _isArrayLike =
/*#__PURE__*/
_curry1(function isArrayLike(x) {
  if (_isArray(x)) {
    return true;
  }

  if (!x) {
    return false;
  }

  if (typeof x !== 'object') {
    return false;
  }

  if (_isString(x)) {
    return false;
  }

  if (x.length === 0) {
    return true;
  }

  if (x.length > 0) {
    return x.hasOwnProperty(0) && x.hasOwnProperty(x.length - 1);
  }

  return false;
});

var XWrap =
/*#__PURE__*/
function () {
  function XWrap(fn) {
    this.f = fn;
  }

  XWrap.prototype['@@transducer/init'] = function () {
    throw new Error('init not implemented on XWrap');
  };

  XWrap.prototype['@@transducer/result'] = function (acc) {
    return acc;
  };

  XWrap.prototype['@@transducer/step'] = function (acc, x) {
    return this.f(acc, x);
  };

  return XWrap;
}();

function _xwrap(fn) {
  return new XWrap(fn);
}

/**
 * Creates a function that is bound to a context.
 * Note: `R.bind` does not provide the additional argument-binding capabilities of
 * [Function.prototype.bind](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind).
 *
 * @func
 * @memberOf R
 * @since v0.6.0
 * @category Function
 * @category Object
 * @sig (* -> *) -> {*} -> (* -> *)
 * @param {Function} fn The function to bind to context
 * @param {Object} thisObj The context to bind `fn` to
 * @return {Function} A function that will execute in the context of `thisObj`.
 * @see R.partial
 * @example
 *
 *      const log = R.bind(console.log, console);
 *      R.pipe(R.assoc('a', 2), R.tap(log), R.assoc('a', 3))({a: 1}); //=> {a: 3}
 *      // logs {a: 2}
 * @symb R.bind(f, o)(a, b) = f.call(o, a, b)
 */

var bind =
/*#__PURE__*/
_curry2(function bind(fn, thisObj) {
  return _arity(fn.length, function () {
    return fn.apply(thisObj, arguments);
  });
});

function _arrayReduce(xf, acc, list) {
  var idx = 0;
  var len = list.length;

  while (idx < len) {
    acc = xf['@@transducer/step'](acc, list[idx]);

    if (acc && acc['@@transducer/reduced']) {
      acc = acc['@@transducer/value'];
      break;
    }

    idx += 1;
  }

  return xf['@@transducer/result'](acc);
}

function _iterableReduce(xf, acc, iter) {
  var step = iter.next();

  while (!step.done) {
    acc = xf['@@transducer/step'](acc, step.value);

    if (acc && acc['@@transducer/reduced']) {
      acc = acc['@@transducer/value'];
      break;
    }

    step = iter.next();
  }

  return xf['@@transducer/result'](acc);
}

function _methodReduce(xf, acc, obj, methodName) {
  return xf['@@transducer/result'](obj[methodName](bind(xf['@@transducer/step'], xf), acc));
}

var symIterator = typeof Symbol !== 'undefined' ? Symbol.iterator : '@@iterator';
function _reduce(fn, acc, list) {
  if (typeof fn === 'function') {
    fn = _xwrap(fn);
  }

  if (_isArrayLike(list)) {
    return _arrayReduce(fn, acc, list);
  }

  if (typeof list['fantasy-land/reduce'] === 'function') {
    return _methodReduce(fn, acc, list, 'fantasy-land/reduce');
  }

  if (list[symIterator] != null) {
    return _iterableReduce(fn, acc, list[symIterator]());
  }

  if (typeof list.next === 'function') {
    return _iterableReduce(fn, acc, list);
  }

  if (typeof list.reduce === 'function') {
    return _methodReduce(fn, acc, list, 'reduce');
  }

  throw new TypeError('reduce: list must be array or iterable');
}

/**
 * Returns a single item by iterating through the list, successively calling
 * the iterator function and passing it an accumulator value and the current
 * value from the array, and then passing the result to the next call.
 *
 * The iterator function receives two values: *(acc, value)*. It may use
 * [`R.reduced`](#reduced) to shortcut the iteration.
 *
 * The arguments' order of [`reduceRight`](#reduceRight)'s iterator function
 * is *(value, acc)*.
 *
 * Note: `R.reduce` does not skip deleted or unassigned indices (sparse
 * arrays), unlike the native `Array.prototype.reduce` method. For more details
 * on this behavior, see:
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#Description
 *
 * Dispatches to the `reduce` method of the third argument, if present. When
 * doing so, it is up to the user to handle the [`R.reduced`](#reduced)
 * shortcuting, as this is not implemented by `reduce`.
 *
 * @func
 * @memberOf R
 * @since v0.1.0
 * @category List
 * @sig ((a, b) -> a) -> a -> [b] -> a
 * @param {Function} fn The iterator function. Receives two values, the accumulator and the
 *        current element from the array.
 * @param {*} acc The accumulator value.
 * @param {Array} list The list to iterate over.
 * @return {*} The final, accumulated value.
 * @see R.reduced, R.addIndex, R.reduceRight
 * @example
 *
 *      R.reduce(R.subtract, 0, [1, 2, 3, 4]) // => ((((0 - 1) - 2) - 3) - 4) = -10
 *      //          -               -10
 *      //         / \              / \
 *      //        -   4           -6   4
 *      //       / \              / \
 *      //      -   3   ==>     -3   3
 *      //     / \              / \
 *      //    -   2           -1   2
 *      //   / \              / \
 *      //  0   1            0   1
 *
 * @symb R.reduce(f, a, [b, c, d]) = f(f(f(a, b), c), d)
 */

var reduce =
/*#__PURE__*/
_curry3(_reduce);

function _pipe(f, g) {
  return function () {
    return g.call(this, f.apply(this, arguments));
  };
}

/**
 * This checks whether a function has a [methodname] function. If it isn't an
 * array it will execute that function otherwise it will default to the ramda
 * implementation.
 *
 * @private
 * @param {Function} fn ramda implementation
 * @param {String} methodname property to check for a custom implementation
 * @return {Object} Whatever the return value of the method is.
 */

function _checkForMethod(methodname, fn) {
  return function () {
    var length = arguments.length;

    if (length === 0) {
      return fn();
    }

    var obj = arguments[length - 1];
    return _isArray(obj) || typeof obj[methodname] !== 'function' ? fn.apply(this, arguments) : obj[methodname].apply(obj, Array.prototype.slice.call(arguments, 0, length - 1));
  };
}

/**
 * Returns the elements of the given list or string (or object with a `slice`
 * method) from `fromIndex` (inclusive) to `toIndex` (exclusive).
 *
 * Dispatches to the `slice` method of the third argument, if present.
 *
 * @func
 * @memberOf R
 * @since v0.1.4
 * @category List
 * @sig Number -> Number -> [a] -> [a]
 * @sig Number -> Number -> String -> String
 * @param {Number} fromIndex The start index (inclusive).
 * @param {Number} toIndex The end index (exclusive).
 * @param {*} list
 * @return {*}
 * @example
 *
 *      R.slice(1, 3, ['a', 'b', 'c', 'd']);        //=> ['b', 'c']
 *      R.slice(1, Infinity, ['a', 'b', 'c', 'd']); //=> ['b', 'c', 'd']
 *      R.slice(0, -1, ['a', 'b', 'c', 'd']);       //=> ['a', 'b', 'c']
 *      R.slice(-3, -1, ['a', 'b', 'c', 'd']);      //=> ['b', 'c']
 *      R.slice(0, 3, 'ramda');                     //=> 'ram'
 */

var slice =
/*#__PURE__*/
_curry3(
/*#__PURE__*/
_checkForMethod('slice', function slice(fromIndex, toIndex, list) {
  return Array.prototype.slice.call(list, fromIndex, toIndex);
}));

/**
 * Returns all but the first element of the given list or string (or object
 * with a `tail` method).
 *
 * Dispatches to the `slice` method of the first argument, if present.
 *
 * @func
 * @memberOf R
 * @since v0.1.0
 * @category List
 * @sig [a] -> [a]
 * @sig String -> String
 * @param {*} list
 * @return {*}
 * @see R.head, R.init, R.last
 * @example
 *
 *      R.tail([1, 2, 3]);  //=> [2, 3]
 *      R.tail([1, 2]);     //=> [2]
 *      R.tail([1]);        //=> []
 *      R.tail([]);         //=> []
 *
 *      R.tail('abc');  //=> 'bc'
 *      R.tail('ab');   //=> 'b'
 *      R.tail('a');    //=> ''
 *      R.tail('');     //=> ''
 */

var tail =
/*#__PURE__*/
_curry1(
/*#__PURE__*/
_checkForMethod('tail',
/*#__PURE__*/
slice(1, Infinity)));

/**
 * Performs left-to-right function composition. The first argument may have
 * any arity; the remaining arguments must be unary.
 *
 * In some libraries this function is named `sequence`.
 *
 * **Note:** The result of pipe is not automatically curried.
 *
 * @func
 * @memberOf R
 * @since v0.1.0
 * @category Function
 * @sig (((a, b, ..., n) -> o), (o -> p), ..., (x -> y), (y -> z)) -> ((a, b, ..., n) -> z)
 * @param {...Function} functions
 * @return {Function}
 * @see R.compose
 * @example
 *
 *      const f = R.pipe(Math.pow, R.negate, R.inc);
 *
 *      f(3, 4); // -(3^4) + 1
 * @symb R.pipe(f, g, h)(a, b) = h(g(f(a, b)))
 * @symb R.pipe(f, g, h)(a)(b) = h(g(f(a)))(b)
 */

function pipe() {
  if (arguments.length === 0) {
    throw new Error('pipe requires at least one argument');
  }

  return _arity(arguments[0].length, reduce(_pipe, arguments[0], tail(arguments)));
}

/**
 * Returns a new list or string with the elements or characters in reverse
 * order.
 *
 * @func
 * @memberOf R
 * @since v0.1.0
 * @category List
 * @sig [a] -> [a]
 * @sig String -> String
 * @param {Array|String} list
 * @return {Array|String}
 * @example
 *
 *      R.reverse([1, 2, 3]);  //=> [3, 2, 1]
 *      R.reverse([1, 2]);     //=> [2, 1]
 *      R.reverse([1]);        //=> [1]
 *      R.reverse([]);         //=> []
 *
 *      R.reverse('abc');      //=> 'cba'
 *      R.reverse('ab');       //=> 'ba'
 *      R.reverse('a');        //=> 'a'
 *      R.reverse('');         //=> ''
 */

var reverse =
/*#__PURE__*/
_curry1(function reverse(list) {
  return _isString(list) ? list.split('').reverse().join('') : Array.prototype.slice.call(list, 0).reverse();
});

/**
 * Performs right-to-left function composition. The last argument may have
 * any arity; the remaining arguments must be unary.
 *
 * **Note:** The result of compose is not automatically curried.
 *
 * @func
 * @memberOf R
 * @since v0.1.0
 * @category Function
 * @sig ((y -> z), (x -> y), ..., (o -> p), ((a, b, ..., n) -> o)) -> ((a, b, ..., n) -> z)
 * @param {...Function} ...functions The functions to compose
 * @return {Function}
 * @see R.pipe
 * @example
 *
 *      const classyGreeting = (firstName, lastName) => "The name's " + lastName + ", " + firstName + " " + lastName
 *      const yellGreeting = R.compose(R.toUpper, classyGreeting);
 *      yellGreeting('James', 'Bond'); //=> "THE NAME'S BOND, JAMES BOND"
 *
 *      R.compose(Math.abs, R.add(1), R.multiply(2))(-4) //=> 7
 *
 * @symb R.compose(f, g, h)(a, b) = f(g(h(a, b)))
 * @symb R.compose(f, g, h)(a)(b) = f(g(h(a)))(b)
 */

function compose() {
  if (arguments.length === 0) {
    throw new Error('compose requires at least one argument');
  }

  return pipe.apply(this, reverse(arguments));
}

export { compose };