Deferred_piping.js

function addOne(n){ return n+1; }
function logger(){ console.log.apply(console,arguments); return  }


//Promise unit
function unit(n){ return $.Deferred().resolve(n); }


//make a simple function into a function that returns a Promise
function lift(fn){
    return function(v){
        return $.Deferred().resolve(fn(v)||v);//if no return value, pass through original value
    };
}

//bind promises together
function bind(apromise, promisefn){
    return apromise.then(function(x){
        return promisefn(x);
    });
}

//[a] -> [a -> [b]] -> [b]
var pipe = function(x, functions) {
    for (var i = 0, n = functions.length; i < n; i++) {
        x = bind(x, functions[i]);
    }
    return x;
};

var liftedAddOne = lift(addOne);
var liftedLog = lift(logger);
var pause1000 = function(val){ return $.Deferred(function(dfd){ window.setTimeout(function(){ dfd.resolve(val); },1000);  }); };


pipe(
    unit(5),//starting point
    [
        liftedAddOne,//list
        liftedAddOne,//of functions
        liftedLog,//that all return chainable promises
        pause1000,//and thus can be .then'd together in a series
        liftedAddOne,//which defines an entire program
        liftedAddOne,
        liftedLog
    ]
).then(null,function(){
    console.log.bind(console,'catch and report errors');
});