Bit of prolog like magic with JavaScript

prolog.js

/*Prolog Num succ and prev defined in some wierd ass JS */

var num= (function(num) {
        num = num || 0;
        var x = num;
        return {
                s: function() {
                        x+=1;
                        return x;
                },  
                p: function() {
                        x-=1;
                        return x;
                }   
        };  
})();
var succ = num.s;
var prev = num.p;
console.log(succ(prev()));