oop_transducers.js

if(typeof require != "undefined") {
    var lodash = require("lodash"),
        _      = require("underscore");
}

var MapTransformer = function(f, nextTransformer) {
    this.f = f;
    this.nextTransformer = nextTransformer;
};

MapTransformer.prototype.init = function() {
    return this.nextTransformer.init();
};

MapTransformer.prototype.result = function(result) {
    return this.nextTransformer.result(result);
};

MapTransformer.prototype.step = function(result, input) {
    return this.nextTransformer.step(result, this.f(input));
};

var MapTransducer = function(f) {
    this.f = f;
};

MapTransducer.prototype.transformer = function(nextTransformer) {
    return new MapTransformer(this.f, nextTransformer);
};

var transduce = function(transducer, builder, init, array) {
    var accumulator = init,
        transformer = transducer.transformer(builder);
    for(var i = 0; i < array.length; i++) {
        accumulator = transformer.step(accumulator, array[i]);
    };
    return transformer.result(accumulator);
};

var ArrayTransformer = function() {};

ArrayTransformer.prototype.result = function(array) {
    return array;
};

ArrayTransformer.prototype.step = function(array, value) {
    array.push(value);
    return array;
};

var inc = function(n) {
    return n + 1;
};

function log() {
    if(typeof console != "undefined") {
        console.log.apply(console, arguments);
    } else {
        print(Array.prototype.slice.call(arguments, 0).join(" "));
    }
}

function time(desc, f) {
    var s = new Date();
    var ret = f();
    log(desc, ret, (new Date())-s, "milliseconds elapsed");
};

var smallArray = [0,1,2,3,4,5,6,7,8,9];

log(smallArray.map(inc));
log(transduce(new MapTransducer(inc), new ArrayTransformer(), [], smallArray));

var largeArray = [];
for(var i = 0; i < 1000000; i++) {
    largeArray.push(i);
}

time("for loop", function() {
    var ret = [];
    for(var i = 0; i < largeArray.length; i++) {
        ret.push(inc(largeArray[i]));
    }
    return ret.length;
});

time("native map", function() {
    return largeArray.map(inc).length;
});

time("transducer", function() {
    return transduce(new MapTransducer(inc), new ArrayTransformer(), [], largeArray).length;
});

if(typeof lodash != "undefined") {
    time("lodash map", function() {
        return lodash.map(largeArray, inc).length;
    });
}

if(typeof _ != "undefined") {
    time("underscore map", function() {
        return _.map(largeArray, inc).length;
    });
}