PHP Tail Recursion

tailrecursion.php

<?php
class TailRecursion {

  private $_function = NULL;
  private $_arguments = array();
  private $_recursing = FALSE;

  private $_recursion = NULL;

  public function __construct(Callable $function) {
    $this->_function = $function;
  }

  public function recursion() {
    return call_user_func_array($this->_recursion, func_get_args());
  }

  public function __invoke() {
    $this->prepare();
    return call_user_func_array($this->_recursion, func_get_args());
  }

  private function prepare() {
    if (NULL === $this->_recursion) {
      $this->_arguments = array();
      $this->_recursing = FALSE;
      $function = $this->_function->bindTo($this);

      $this->_recursion = function() use ($function) {

        $this->_arguments[] = func_get_args();

        if (!$this->_recursing) {
          $this->_recursing = TRUE;

          while ($this->_arguments) {
            $result = call_user_func_array($function, array_shift($this->_arguments));
          }
          $this->_recursing = FALSE;
          return $result;
        }
      };
    }
  }
}

$facOne = new TailRecursion(
  function ($n, $acc = 1) {
    if ($n == 1) {
      return $acc;
    }
    return $this->recursion($n - 1, $acc * $n);
  }
);
var_dump($facOne(4));



/**
 * possible, but useful?
 */
class NestedRecursion {

  private $_function = NULL;

  public function __construct(Callable $function) {
    $this->_function = $function;
  }

  public function __invoke() {
    return call_user_func_array(array($this, 'recursion'), func_get_args());
  }

  public function recursion() {
    $function = $this->_function->bindTo($this);
    return call_user_func_array($function, func_get_args());
  }
}

$facTwo = new NestedRecursion(
  function ($n, $acc = 1) {
    if ($n == 1) {
      return $acc;
    }
    return $this->recursion($n - 1, $acc * $n);
  }
);
var_dump($facTwo(4));