Recursion with anonymous function [duplicate]

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Closed 9 years ago.

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javascript: recursive anonymous function?
Anonymous recursive PHP functions

I was wondering... Is it possible to do recursion with anonymous function?

Here is one example: I need to get six-chars long string which may contain only numbers and spaces. The only rules are that it cannot start or end with spaces. We check for that and if that occurs - just call recursion on the same, anonymous, function. Just how!?

function() {

    $chars   = range(0, 9);
    $chars[] = ' ';
    length   = 6;
    $count   = count($chars);

    $string = '';
    for ($i = 0; $i < $length; ++$i) {

        $string .= $chars[mt_rand(0, $count - 1)];

    }

    $string = trim($string);

    if (strlen($string) !== $length) { // There were spaces in front or end of the string. Shit!

        // Do recursion.

    }

    return $string;

}

Answer 1

Yes it is, but I wouldn't recommend it as it's a bit tricky ;)

First possibility:

<?php
$some_var1="1";
$some_var2="2";
function($param1, $param2) use ($some_var1, $some_var2)
{
    call_user_func(__FUNCTION__, $other_param1, $other_param2);
}
?>

Another one:

<?php 
$recursive = function () use (&$recursive){ 
    // The function is now available as $recursive 
} 
?> 

Examples taken from http://php.net/

Answer 2

The answer is complicated but not impossible. It took me several minutes to figure out. We first must define a utility function called $combinator().

The solution to your problem:

$combinator(
function($self) { function() use (&$self) {
    $chars   = range(0, 9);
    $chars[] = ' ';
    length   = 6;
    $count   = count($chars);

    $string = '';
    for ($i = 0; $i < $length; ++$i) {
        $string .= $chars[mt_rand(0, $count - 1)];
    }
    $string = trim($string);

    if (strlen($string) !== $length) {
        return $self();
    }
    return $string;
} }
);

The definition of $combinator():

$combinator = function($principle)
{
  (function($transept) use (&$principle)
  {
    $principle(
      function($arguments) use (&$transept)
      {
        call_user_func_array($transept($transept), $arguments));
      }
    );
  })
  (function($transept) use (&$principle)
  {
    $principle(
      function($arguments)
      {
        call_user_func_array($transept($transept), $arguments);
      }
    );
  });
}

Answer 3

A much saner method to do the same thing. Requires only one loop as well.

$chars = array_merge(range(0, 9), array(' '));

$string = mt_rand(0, 9);
for ($i = 1; $i <= 4; $i++) {
    $string .= $chars[array_rand($chars)];
}
$string .= mt_rand(0, 9);

Sorry for sidestepping the actual question though.

Answer 4

use goto

function() {
    start:
    $chars   = range(0, 9);
    $chars[] = ' ';
    length   = 6;
    $count   = count($chars);

    $string = '';
    for ($i = 0; $i < $length; ++$i) {

        $string .= $chars[mt_rand(0, $count - 1)];

    }

    $string = trim($string);

    if (strlen($string) !== $length) { // There were spaces in front or end of the string. Shit!

        goto start;

    }

    return $string;

But it's not the best idea to use goto.