pure-log.js

/********** first version **********/

function double(x) {
    return (x * 2);
}

double(double(1)); // => 4



/********** add log function! **********/

function double(x, log) {
    return [(x * 2), (log + "calling double(" + x + ")!\n")];
}

var result_1 = double(1, "");
var result_2 = double(result_1[0], result_1[1]);  // wtf?!


/********** functional pattern **********/

function make_loggable(x, log) {
    return [x, log];
}

function chain(loggable, f) {
    var r = f(loggable[0]);
    return make_log(r[0], loggable[1] + r[1]);
}

function double(x) {
    return make_log(x * 2, "calling double(" + x + ")!\n");
}

chain(chain(make_loggable(1, ""), double), double); 
// with syntatic sugar, we can write something like: make_loggable(1, "") >>= double >>= double