Created
September 23, 2014 05:14
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TRANSducers!
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| // function reducing(acc, next) { | |
| // return next_acc | |
| // } | |
| // function transducing(reducing) { | |
| // return more_reducing | |
| // } | |
| // Example reducer (without transducers) | |
| // function incrPrintConcat() { | |
| // var i = 0 | |
| // return function (acc, val) { | |
| // console.log(i, val, acc) | |
| // return (acc||[]).concat(val+1) | |
| // } | |
| // } | |
| // | |
| // With transducers: | |
| // tcomp(map(function (x) { return x+1 }), | |
| // forEach(function (acc, val, i) { console.log(i, val, acc) }), | |
| // concat) | |
| // Perform transduction | |
| Array.prototype.transduce = function (f, init) { | |
| return this.reduce(f(), init) | |
| } | |
| Object.prototype.transduce = function (f, init) { | |
| var obj = this | |
| return Object.keys(obj).transduce(tcomp(map(function (key) { return [key, obj[key]] }), f), init) | |
| } | |
| // Compose transducers | |
| function tcomp(f) { | |
| var gs = Array.prototype.slice.call(arguments, 1) | |
| while (gs.length) | |
| f = (function (ff, g) { | |
| return function (x) { return ff(g(x)) } | |
| })(f, gs.shift()) | |
| return f | |
| } | |
| // Modifier transducers | |
| function forEach(f) { | |
| return function (next) { | |
| return function (acc, val, i) { | |
| f(acc, val, i) | |
| return next(acc, val, i) | |
| } | |
| } | |
| } | |
| function map(f) { | |
| return function (next) { | |
| return function (acc, val, i) { | |
| return next(acc, f(val, i), i) | |
| } | |
| } | |
| } | |
| function filter(f) { | |
| return function (next) { | |
| return function (acc, val, i) { | |
| if (f(val, i)) | |
| return next(acc, val, i) | |
| else | |
| return acc | |
| } | |
| } | |
| } | |
| function take(n) { | |
| return filter(function (val, i) { | |
| return i < n | |
| }) | |
| } | |
| function takeWhile(f) { | |
| var taking = true | |
| return filter(function (val, i) { | |
| return taking && (taking = f(val, i)) | |
| }) | |
| } | |
| function drop(n) { | |
| return filter(function (val, i) { | |
| return i >= n | |
| }) | |
| } | |
| function dropWhile(f) { | |
| var taking = false | |
| return filter(function (val, i) { | |
| return taking || (taking = f(val, i)) | |
| }) | |
| } | |
| function takeNth(n) { | |
| return filter(function (val, i) { | |
| return i === n | |
| }) | |
| } | |
| function attrgetter(name) { | |
| return map(function (obj) { | |
| return obj[name] | |
| }) | |
| } | |
| function itemgetter(i) { | |
| return map(function (arr) { | |
| return arr[i] | |
| }) | |
| } | |
| // Accumulating transducers | |
| function concat() { | |
| return function () { | |
| return function (acc, val) { | |
| return (acc||[]).concat(val) | |
| } | |
| } | |
| } | |
| function objectify(keyf) { | |
| return function () { | |
| return function (acc, val, i) { | |
| acc = acc || {} | |
| acc[keyf(val, i)] = val | |
| return acc | |
| } | |
| } | |
| } | |
| console.log([1,2,3].transduce(tcomp(map(function(x){return x+1}), concat()), [])) | |
| console.log({a:'b',c:'d',e:'f'}.transduce( | |
| tcomp(itemgetter(1), | |
| drop(1), | |
| map(function (letter) { return letter.toUpperCase() }), | |
| objectify(function(x) {return x.toLowerCase()})))) |
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