delegation by composition #07

var first = (function() {
    var chainNames = ["then", "andThen", "next"];
    var endChainNames = ["finally", "andFinally", "last"];
    var chain = function(fn) {
        var f1 = function(g) {
            var func = function() {return g.call(this,
                    fn.apply(this, arguments));};
            chain(func);
            return func;
        };
        var f2 = function(g) {
            return function() {return g.call(this,
                    fn.apply(this, arguments));};
        };
        chainNames.forEach(function(name) {fn[name] = f1;});
        endChainNames.forEach(function(name) {fn[name] = f2;});
    };
    return function(f) {
        var fn = function() {
            return f.apply(this, arguments);
        };
        chain(fn);
        return fn;
    };
}());



var add1 = function(x) {return x + 1;};
var mult2 = function(x) {return x * 2;};
var square = function(x) {return x * x;};
var negate = function(x) {return -x;};


var f = first(add1).then(mult2).andThen(square).andFinally(negate);

var g = first(mult2).next(add1).then(negate).then(mult2)
                    .then(add1).last(square);

console.log(f(2));
console.log(g(3));

-Explicit Ordering Implementation
-This API makes a miniature DSL out of functional composition, always starting with "first", followed by any number of "then", "andThen", or "next" clauses, optionally concluding with "finally", "last", or "andFinally".

• Extract from: http://scott.sauyet.com/Javascript/Talk/Compose/2013-05-22/#slide-28