<?php
    function make_path_from_bits() {
        //Accepts $sep (separator, eg "/"), followed by the filenames.
        $bits = func_get_args();    // all the arguments into an array
        $sep = array_shift($bits);  // arg1 is the separator, the rest are the files
        $p = implode($sep,$bits);
        $double = $sep . $sep;
        while (strpos($p,$double) !== false) {
            $p = str_replace($double, $sep, $p);
        }
        return $p;
    }

$webroot = "/";
$myfile = "/styles/my.css";
$data = "data/"

$fullpath = make_path_from_bits("/",$webroot,$data,$myfile);
echo $fullpath;