Conert to boolean by using normal PHP falsey equivalencies with the addition of string 'false' which PHP usually considers truthy.

bool.function.php

/**
 * Conert to boolean by using normal PHP falsey equivalencies with
 * the addition of string 'false' which PHP usually considers truthy.
 *
 * @param   mixed   $val        Value to convert to boolean
 * @return  boolean             Boolean equivalent
 */
function bool($val)
{
    if (
        $val === '' ||
        $val === 'false' ||
        $val === '0' ||
        $val === 0 ||
        $val === null ||
        $val === array() ||
        $val === 0.0 ||
        $val === false
    ) {
        return false;
    }
    
    return true;
}