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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>JavaScript Transducers</title>
<meta name="description" content="A framework for easily creating beautiful presentations using HTML">
<meta name="author" content="Hakim El Hattab">
<meta name="apple-mobile-web-app-capable" content="yes" />
<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no, minimal-ui">
<link rel="stylesheet" href="css/reveal.css">
<link rel="stylesheet" href="css/theme/black.css" id="theme">
<!-- Code syntax highlighting -->
<link rel="stylesheet" href="lib/css/zenburn.css">
<!-- Printing and PDF exports -->
<script>
var link = document.createElement( 'link' );
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = window.location.search.match( /print-pdf/gi ) ? 'css/print/pdf.css' : 'css/print/paper.css';
document.getElementsByTagName( 'head' )[0].appendChild( link );
</script>
<!--[if lt IE 9]>
<script src="lib/js/html5shiv.js"></script>
<![endif]-->
</head>
<body>
<div class="reveal">
<!-- Any section element inside of this container is displayed as a slide -->
<div class="slides">
<section data-markdown>
<script type="text/template">
# JavaScript Transducers
by **Matias Volpe**
@matvolpe
<a href="http://ar.linkedin.com/in/matiasvolpe">ar.linkedin.com/in/matiasvolpe</a>
<br/>
https://github.com/kratico/jsconf-uy-2015
</script>
</section>
<section>
<blockquote>
Logic will get you from A to B.
<br/>
Imagination will take you everywhere.
</blockquote>
<p class="fragment">Albert Einstein</p>
</section>
<section>
<h2>Problem</h2>
<ul>
<li class="fragment">
I want to reuse data transformation logic without having to re-implement the transformation process for each data-type
</li>
<li class="fragment">
And I want it to be fast
</li>
<li class="fragment">
And I want it to be efficient
</li>
</ul>
</section>
<section data-markdown>
<script type="text/template">
## What are transducers?
Transducers are a powerful and **composable** way to build algorithmic
**transformations** that you can **reuse** in many **contexts**
</script>
</section>
<section data-markdown>
<script type="text/template">
## What are transducers?
* Transducers are composable algorithmic transformations.
* They are independent from the context of their input and output
sources and specify only the essence of the transformation in
terms of an individual element.
* Because transducers are decoupled from
input or output sources, they can be used in many different
processes - collections, streams, channels, observables, etc.
* Transducers compose directly, without awareness of input or
creation of intermediate aggregates.
</script>
</section>
<section>
<section>
<h2>Benchmark</h2>
<pre>
<code class="javascript">
input.map(addTen)
.map(double)
.filter(multipleOfFive)
.filter(even);
_(input)
.map(addTen)
.map(double)
.filter(multipleOfFive)
.filter(even)
.value();
</code>
</pre>
</section>
<section>
<h2>Benchmark</h2>
<pre>
<code class="javascript">
transduce(
// Transducer
compose(
map(addTen),
map(double),
filter(multipleOfFive),
filter(even)
),
append,
[],
input
);
</code>
</pre>
</section>
<section>
<h2>Benchmark</h2>
<img src="images/benchmark.png"></img>
<small>http://jlongster.com/Transducers.js-Round-2-with-Benchmarks</small>
</section>
<section data-markdown>
## Benchmark
```
// Intermediate allocations
var gArr = arr.map(g);
// [g(a1), g(a2),...]
var fgArr = gArr.map(f);
// [f(ga1), f(ga2),...]
// No intermediate allocations
var fg = compose(f, g);
var fgArr = arr.map(fg);
// [fg(a1), fg(a2),...]
// How can I compose filter, take, drop,...?
```
</section>
</section>
<section data-markdown>
<script type="text/template">
## Transduce
> transduce = transform + reduce
* The word `transduce` is just a combination of `transform` and `reduce`.
* The `reduce` function is the base transformation; any other
transformation can be expressed in terms of it (map, filter, etc).
</script>
</section>
<section data-markdown>
<script type="text/template">
## Array.prototype.reduce()
The `reduce()` method applies a function against an accumulator and
each value of the array (from left-to-right) has to reduce it to a
single value.
</script>
</section>
<section data-markdown>
<script type="text/template">
```
var input = [1, 2, 3, 4];
// The function passed to reduce is a reducing function
output = input.reduce(function(result, x) {
result.push(x + 1);
return result;
}, []);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Reducing function
It is important to remember that `reduce`:
* Starts with an initial value
* Operates on one item at a time with the reducing function using
* The initial value for result in the first step
* The return value of the step function for result of next iteration
* Outputs a value using the last computed result.
</script>
</section>
<section data-markdown>
<script type="text/template">
## Transform
```
var input = [1, 2, 3, 4];
// The essence of the transformation
var plus1 = function(x) {
return x + 1;
}
output = input.reduce(function(result, x) {
result.push(plus1(x));
return result;
}, []);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Separation of concerns
```
var input = [1, 2, 3, 4];
var plus1 = function(x) {
return x + 1;
};
var reduce = function(reducingFn, init, input) {
return input.reduce(reducingFn, init);
};
output = reduce(function(result, x) {
result.push(plus1(x));
return result;
}, [], input);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Separation of concerns
```
var input = [1, 2, 3, 4];
var plus1 = function(x) {
return x + 1;
};
var reduce = function(reducingFn, init, input) {
return input.reduce(reducingFn, init);
};
var append = function(result, input) {
result.push(input);
return result;
};
output = reduce(function(result, x) {
return append(result, plus1(x));
}, [], input);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Transduce
```
var input = [1, 2, 3, 4];
var plus1 = function(x) {
return x + 1;
};
var reduce = function(reducingFn, init, input) {
return input.reduce(reducingFn, init);
};
var append = function(result, input) {
result.push(input);
return result;
};
// plus1Transducer
output = transduce(plus1Transducer, append, [], input);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section>
<h2>Transducer signature</h2>
<pre>
<code class="javascript">
// A transducer takes a reducing function
// and returns a new reducing function
var transducer = function(reduceFn) {
returns function(result, input) {
// ... do sommething with reduceFn ...
}
}
</code>
</pre>
</section>
<section>
<section data-markdown>
<script type="text/template">
## Map Transducer
```
// Map Transducer
var mapping = function(f) {
return function(reduce) {
return function(result, input) {
return reduce(result, f(input));
};
};
};
var transduce = function(xform, f, init, input) {
return reduce(xform(f), init, input);
};
output = transduce(mapping(plus1), append, [], input);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Array.prototype.map
```
var input = [1, 2, 3, 4];
var plus1 = function(x) {
return x + 1;
}
var output = input.map(plus1);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## map(f, xs)
```
var input = [1, 2, 3, 4];
var plus1 = function(x) {
return x + 1;
};
var map = function(transform, xs) {
return xs.reduce(
// Reducing function
function(result, input) {
return append(result, transform(input));
},
[]);
}
var output = map(plus1, input);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## mapper(f)
```
var input = [1, 2, 3, 4];
var plus1 = function(x) {
return x + 1;
}
var mapper = function(transform) {
return function(result, input) {
return append(result, transform(input));
};
};
var output = input.reduce(mapper(plus1));
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## mapping(f)
```
var input = [1, 2, 3, 4];
var plus1 = function(x) {
return x + 1;
};
// Map Transducer
var mapping = function(transform) {
return function(reduce) {
return function(result, input) {
return reduce(result, transform(input));
};
};
}
var output = input.reduce(mapping(plus1)(append), []);
// output = [ 2, 3, 4, 5 ]
```
</script>
</section>
</section>
<section>
<section data-markdown>
<script type="text/template">
## Filter Transducer
```
// Filter transducer
var filtering = function(predicate) {
return function(reduce) {
return function(result, input) {
return predicate(input) ?
reduce(result, input) :
result;
};
};
}
var input = [1, 2, 3, 4];
var isOdd = function(x) {
return x % 2 === 0;
};
var output = input.reduce(filtering(isOdd)(append), []);
// output = [2, 4]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Array.prototype.filter
```
var input = [1, 2, 3, 4];
var isOdd = function(x) {
return x % 2 === 0;
};
var output = input.filter(isOdd);
// output = [2, 4]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## filter(predicate, xs)
```
var input = [1, 2, 3, 4];
var isOdd = function(x) {
return x % 2 === 0;
};
var filter = function(predicate, xs) {
return xs.reduce(
function(result, input) {
return predicate(input) ?
append(result, input) :
result
},
[]
);
};
var output = filter(isOdd, input);
// output = [2, 4]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## filterer(predicate)
```
var input = [1, 2, 3, 4];
var isOdd = function(x) {
return x % 2 === 0;
};
var filterer = function(predicate) {
return function(result, input) {
return predicate(input) ?
append(result, input) :
result;
}
};
var output = input.reduce(filterer(isOdd), []);
// output = [2, 4]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## filtering(predicate)
```
var input = [1, 2, 3, 4];
var isOdd = function(x) {
return x % 2 === 0;
};
// Filter transducer
var filtering = function(predicate) {
return function(reduce) {
return function(result, input) {
return predicate(input) ?
reduce(result, input) :
result;
};
};
}
var output = input.reduce(filtering(isOdd)(append), []);
// output = [2, 4]
```
</script>
</section>
</section>
<section>
<h1>Transducer Composition</h1>
</section>
<section data-markdown>
<script type="text/template">
## Composition
```
var input = [1, 2, 3, 4, 5];
// Could we use function composition?
var transducer = mapping(plus1)(
filtering(isOdd)
);
var output = transduce(transducer, append, [], input);
// output = [2, 4, 6]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Function composition
> (f ∘ g)(x) = f(g(x))
</script>
</section>
<section data-markdown>
<script type="text/template">
## Compose
```
function compose() {
var fns = Array.prototype.slice.call(arguments);
return function(x) {
var value = x;
for (var i = fns.length - 1; i >= 0; i--) {
value = fns[i](value);
}
return value;
};
}
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Compose
```
var plus1 = function(x) {
return x + 1;
}
var plus2 = compose(plus1, plus1);
var output = plus2(2);
// output = 4
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Transducer composition
```
var input = [1, 2, 3, 4, 5];
var transducer = compose(
mapping(plus1),
filtering(isOdd)
);
var output = transduce(transducer, append, [], input);
// output = [2, 4, 6]
```
</script>
</section>
<section data-markdown>
<script type="text/template">
# Stateful transducers
</script>
</section>
<section data-markdown>
<script type="text/template">
## drop(n)
```
var input = [1, 2, 3, 4, 5];
var drop = function drop(n) {
return function(reduce) {
return function(result, input) {
if (n > 0) {
n--;
} else {
result = reduce(result, input);
}
return result;
};
};
};
var transducer = compose(
mapping(plus1),
filtering(isOdd),
drop(1)
);
var output = transduce(transducer, append, [], input);
// output = [4, 6]
```
</script>
</section>
<section>
<section data-markdown>
<script type="text/template">
## Early termination
```
var transduce = function(xform, f, init, input) {
return reduce(xform(f), init, input);
};
var reduce = function(reducingFn, init, input) {
// How can we break the reduce process?
return input.reduce(reducingFn, init);
};
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Early termination
```
var transduce = function(xform, f, init, input) {
return reduce(xform(f), init, input);
};
var reduce = function(reducingFn, init, input) {
return arrayReduce(reducingFn, init, input);
};
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Early termination
```
var arrayReduce = function(xf, init, array) {
var result = init,
i = 0,
length = array.length;
for (; i < length; i++) {
result = xf(result, array[i]);
if(isReduced(result)) {
result = deref(result);
break;
}
}
return result;
}
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Early termination
ES6 Iterator Protocol
```
var iterableReduce = function(xf, init, iterable)
var result = init,
iter = iterable,
val = iter.next();
while(!val.done) {
result = xf(result, val.value);
if(isReduced(result)) {
result = deref(result);
break;
}
val = iter.next();
}
return result;
}
```
</script>
</section>
<section data-markdown>
<script type="text/template">
## Early termination
```
function reduced(value) {
return {
value: value,
__transducers_reduced__: true
};
}
function isReduced(value) {
return value && value.__transducers_reduced__;
}
function deref(reducedValue) {
return reducedValue.value;
}
```
</script>
</section>
</section>
<section data-markdown>
<script type="text/template">
## take(n)
```
var input = [1, 2, 3, 4, 5];
var take = function(n) {
return function(reduce) {
return function(result, input) {
result = reduce(result, input);
if (--n <= 0) {
result = reduced(result);
}
return result;
};
};
}
var transducer = compose(
mapping(plus1),
filtering(isOdd),
drop(1)
take(1)
);
var output = transduce(transducer, append, [], input);
// output = [4]
```
</script>
</section>
<section>
<h1>Examples</h1>
</section>
<section>
<section data-markdown>
## Array to Object
Counting #hashtags
```
var input = [
{ username: 'Balda', text: 'some #cool hashtag' },
{ username: 'Pami', text: 'other #good hashtag' },
{ username: 'Cohen0', text: '#transducers FTW' },
{ username: 'Perotti', text: '#cool' },
{ username: 'Zyrko', text: 'no hashtag' },
{ username: 'Novoa', text: 'What are #transducers ?' }
];
var transducer = compose(...);
var append = function(result, input) {...};
var output = transduce(transducer, append, {}, input);
// output = { '#cool': 2, '#good': 1, '#transducers': 2 }
```
</section>
<section data-markdown>
## Array to Object
Counting #hashtags
```
var transducer = compose(
filtering(function(tweet) {
// Filter tweets with hashtag
return tweet.text.match(/#\w+/);
}),
mapping(function(tweet) {
// Return the #hashtag text
return tweet.text.match(/#\w+/g)[0];
})
);
var append = function(result, input) {
result[input] = result[input] || 0;
result[input]++;
return result;
};
```
</section>
</section>
<section>
<section data-markdown>
## Generator to Object
Counting #hashtags
```
var input = function* () {
yield { username: 'Balda', text: 'some #cool hashtag' };
yield { username: 'Pami', text: 'other #good hashtag' };
yield { username: 'Cohen0', text: '#transducers FTW' };
yield { username: 'Perotti', text: '#cool' };
yield { username: 'Zyrko', text: 'no hashtag' };
yield { username: 'Novoa', text: 'What are #transducers ?' };
};
var transducer = compose(...);
var append = function(result, input) {...};
var output = transduce(transducer, append, {}, input());
// output = { '#cool': 2, '#good': 1, '#transducers': 2 }
```
</section>
<section data-markdown>
## Generator to Object
Counting #hashtags
```
var transducer = compose(
filtering(function(tweet) {
// Filter tweets with hashtag
return tweet.text.match(/#\w+/);
}),
mapping(function(tweet) {
// Return the #hashtag text
return tweet.text.match(/#\w+/g)[0];
})
);
var append = function(result, input) {
result[input] = result[input] || 0;
result[input]++;
return result;
};
```
</section>
</section>
<section>
<section data-markdown>
## Generator to Array
Counting #hashtags
```
var input = function* () {
yield { username: 'Balda', text: 'some #cool hashtag' };
yield { username: 'Pami', text: 'other #good hashtag' };
yield { username: 'Cohen0', text: '#transducers FTW' };
yield { username: 'Perotti', text: '#cool' };
yield { username: 'Zyrko', text: 'no hashtag' };
yield { username: 'Novoa', text: 'What are #transducers ?' };
};
var transducer = compose(...);
var append = function(result, input) {...};
var output = transduce(transducer, append, [], input());
// output = [ ['#cool', 2], ['#good', 1], ['#transducers': 2] ]
```
</section>
<section data-markdown>
## Generator to Array
Counting #hashtags
```
var transducer = compose(
filtering(function(tweet) {
// Filter tweets with hashtag
return tweet.text.match(/#\w+/);
}),
mapping(function(tweet) {
// Return the #hashtag text
return tweet.text.match(/#\w+/g)[0];
})
);
var append = function(result, hashtag) {
var hashtagCount = findByHashtag(hashtag, result);
if (!hashtagCount) {
hashtagCount = [hashtag, 1];
result.push(hashtagCount);
} else {
hashtagCount[1]++;
}
return result;
};
```
</section>
</section>
<section>
<section data-markdown>
## Streams
Streaming numbers
```
arrayStream(['1', '2', '3', '4', '5'])