pairs.js

function cons(a,b) {
    return function (selector) {
        if (selector=='areyoualist?')
            return 'yesIam';
        return selector(a,b);
    };
}

function car(list) {
    function carHelper(a,b) {
        return a;
    }
    return list(carHelper);
}

function cdr(list) {
    function cdrHelper(a,b) {
        return b;
    }
    return list(cdrHelper);
}

function isList(thing) {
    if (typeof(thing)!='function')
        return false;
    try {
        if (thing('areyoualist?')=='yesIam')
        return true;
    } catch(e) {
    }
    return false;
}

function show(list) {
    var sval;
    if (list==null)
        sval = '()';
    else if (isList(list))
        sval = '('+ show(car(list)) +' '+show(cdr(list))+')';
    else 
        sval = String(list);
    return sval;
}