Übergibson

The “while” loop is an ubiquitous feature of most programming languages. In languages with C-like syntax like Java and PHP it takes the form:

while( expression )
statement

In languages that support the evaluation of strings as source code, you can, using recursion, construct your own whiledo() function. Consider the following PHP function:

function whiledo($while, $do)
{
	if(eval("return ".$while)) {
		eval($do);
		whiledo($while, $do);
	}
}

$while is the expression to evaluate, and if it evaluates to true (in PHP this is any nonzero integer, any nonempty string, or the NULL constant) eval($do) is called and a recursive call to whiledo() is made.

Should eval(“return “.$while) evaluate to anything non-true, the block is skipped and the function stops calling itself.

Bizarre, no? To test the function it gets a bit nasty because the inner-function eval() call necessitates global variables. Try this:

<?
/*
 * The "while, do" function
 * Inner-function eval() necessitates globals
 */
global $i, $lim;
function whiledo($while, $do) {
	if(eval("return ".$while)) {
		eval($do);
		whiledo($while, $do);
	}
}
$i = 0;
$lim = 10;
whiledo('$GLOBALS[\'i\'] < $GLOBALS[\'lim\'];', '
	++$GLOBALS[\'i\'];
	echo $GLOBALS[\'i\']."\n";	
');
?>