array_product

This function can be used to test if all values in an array of booleans are TRUE.
Consider:
<?php
function outbool($test)
{
 return (bool) $test;
}
$check[] = outbool(TRUE);
$check[] = outbool(1);
$check[] = outbool(FALSE);
$check[] = outbool(0);
$result = (bool) array_product($check);
// $result is set to FALSE because only two of the four values evaluated to TRUE
?>

The above is equivalent to:
<?php
$check1 = outbool(TRUE);
$check2 = outbool(1);
$check3 = outbool(FALSE);
$check4 = outbool(0);
$result = ($check1 && $check2 && $check3 && $check4);
?>

This use of array_product is especially useful when testing an indefinite number of booleans and is easy to construct in a loop.

Here's how you can find a factorial of a any given number with help of range and array_product functions.
function factorial($num) {
 return array_product(range(1, $num));
}
printf("%d", factorial(5)); //120

Just a little correction for Andre D's answer: "(bool) array_product($array);" is equivalent with the conjunction of each array elements of $array, UNLESS the provided array is empty in which case array_product() will return 1, which will translate to boolean TRUE.
To mitigate this, you should expand the function with an additional check:
<?php
$result = !empty($check) && !!array_product($check);
?>

You can use array_product() to calculate the geometric mean of an array of numbers: 
<?php
$a = [ 1, 10, 100 ];
$geom_avg = pow( array_product( $a ), 1 / count( $a ));
// = 9.999999999999998 ≈ 10
?>

You can use array_product to calculate the factorial of n:
<?php
function factorial( $n )
{
 if( $n < 1 ) $n = 1;
 return array_product( range( 1, $n ));
}
?>

If you need the factorial without having array_product available, here is one:
<?php
function factorial( $n )
{
 if( $n < 1 ) $n = 1;
 for( $p++; $n; ) $p *= $n--;
 return $p;
}
?>