billhails

{
    // very simple environment, one binding per frame
    typedef environment { frame(string, expression, environment) | root }
    
    // lookup access to the environment
    fn lookup {
        (str, frame(str, value, _)) { value }
        (str, frame(_, _, parent))  { lookup(str, parent) }
        (str, root)                 { error("mce symbol not defined " @@ str) }
    }

billhails

<?php

function factorial($n) {
    if ($n === 0) {
        return 1;
    } else {
        return $n * factorial($n - 1);
    }
}