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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8"/>
<title>Building A Program</title>
<meta name="author" content="(Bill Carlson)"/>
<style type="text/css">
.underline { text-decoration: underline; }
</style>
<link rel="stylesheet" href="./reveal.js/css/reveal.css"/>
<link rel="stylesheet" href="./reveal.js/css/theme/sky.css" id="theme"/>
<link rel="stylesheet" href="./reveal.js/lib/css/zenburn.css"/>
<!-- If the query includes 'print-pdf', include the PDF print sheet -->
<script>
if( window.location.search.match( /print-pdf/gi ) ) {
var link = document.createElement( 'link' );
link.rel = 'stylesheet';
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link.href = './reveal.js/css/print/pdf.css';
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}
</script>
</head>
<body>
<div class="reveal">
<div class="slides">
<section id="sec-title-slide"><h1>Building A Program</h1>
</section>
</section>
</section>
<section>
<section id="slide-org6cc8bf3">
<h3 id="org6cc8bf3">About Me</h3>
<div class="outline-text-3" id="text-org6cc8bf3">
</div>
</section>
<section id="slide-org3d9255b">
<h4 id="org3d9255b">Bill Carlson</h4>
</section>
<section id="slide-org72ce98e">
<h4 id="org72ce98e">Cotiviti Labs</h4>
</section>
<section id="slide-orga3b576c">
<h4 id="orga3b576c"><a href="https://www.facebook.com/BungalowJax/">The Bungalow</a></h4>
<img src="bungalow.png" width="400"/>
</section>
</section>
<section>
<section id="slide-orgb2e047a">
<h3 id="orgb2e047a">Last Time in "Functional Programming"</h3>
<ul class="fragment">
<li>Programming with functions</li>
</ul>
<ul class="fragment">
<li>Referential transparency</li>
</ul>
</section>
<section >
<p>
A program is <i>evaluated</i> by repeated substitution of function calls with the values they represent.
</p>
</section>
<section >
<p>
The code is simply an interpreter for a particular algebra. The program is the data that gets evaluated.
</p>
</section>
<section >
<p>
But how do you actually <i>build</i> the program?
</p>
</section>
</section>
<section>
<section id="slide-org35aa41d">
<h2 id="org35aa41d">Data Types Revisited</h2>
<p>
Standard Types
</p>
<ul>
<li><code>Int</code></li>
<li><code>String</code></li>
</ul>
<p>
Higher-Kinded Types
</p>
<ul>
<li><code>Option[A]</code></li>
<li><code>List[A]</code></li>
<li><code>Either[E, A]</code></li>
</ul>
</section>
</section>
<section>
<section id="slide-org2dd928e">
<h2 id="org2dd928e">Typeclasses</h2>
<div class="outline-text-2" id="text-org2dd928e">
</div>
</section>
<section id="slide-orgc146b08">
<h4 id="orgc146b08">Typeclasses</h4>
<ul>
<li>Typeclasses are a mechanism to allow for <b>ad-hoc polymorphism</b></li>
<li>The typeclass declares an interface</li>
<li>THe instance defines the operations</li>
</ul>
</section>
<section id="slide-orgffa4034">
<h4 id="orgffa4034">Typeclasses allow you to modify behavior of code you don't own.</h4>
</section>
<section id="slide-org4db76d3">
<h4 id="org4db76d3">Typeclasses</h4>
<div class="org-src-container">
<pre><code class="scala" >trait Show[A] {
def show(a: A): String
}
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >implicit val stringShow = new Show[String] {
def show(s: String) = s
}
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >implicit val addressShow = new Show[Address] {
def show(addr: Address) =
s"""|${addr.street}
|${addr.city} ${addr.state} ${addr.zip}""".stripMargin
}
</code></pre>
</div>
</section>
<section id="slide-org27e0b96">
<h4 id="org27e0b96">Typeclasses</h4>
<div class="org-src-container">
<pre><code class="scala" >// A polymorphic function that works only when there is an implicit
// instance of Show[A] available
def log[A](a: A)(implicit s: Show[A]) = println(s.show(a))
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >object Show {
def apply[A] = implicitly[Show[A]]
}
def log[A : Show](a: A) = println(Show[A].show(a))
</code></pre>
</div>
</section>
</section>
<section>
<section id="slide-orgd62c999">
<h2 id="orgd62c999">Algebraic Combinators</h2>
<div class="outline-text-2" id="text-orgd62c999">
</div>
</section>
</section>
<section>
<section id="slide-orgfbfc81c">
<h3 id="orgfbfc81c">Monoid</h3>
<div class="org-src-container">
<pre><code class="scala" >trait Monoid[A] {
val zero: A
def append(a: A, b: A)): A
}
</code></pre>
</div>
</section>
<section id="slide-org3837756">
<h4 id="org3837756">String concatenation</h4>
<div class="org-src-container">
<pre><code class="scala" >val stringConcat = new Monoid[String] {
val zero: String = ""
def append(a: String, b: String)) = a + b
}
</code></pre>
</div>
</section>
<section id="slide-org7607d64">
<h4 id="org7607d64">Integer Addition</h4>
<div class="org-src-container">
<pre><code class="scala" >val additionMonoid = new Monoid[Int] {
val zero: Int = 0
def append(a: Int, b: Int)) = a + b
}
</code></pre>
</div>
</section>
<section id="slide-org83ca564">
<h4 id="org83ca564">Integer Multiplication</h4>
<div class="org-src-container">
<pre><code class="scala" >val multiplicationMonoid = new Monoid[Int] {
val zero: Int = 1
def append(a: Int, b: Int)) = a * b
}
</code></pre>
</div>
</section>
<section id="slide-org821d3ff">
<h4 id="org821d3ff">Laws</h4>
<p>
Right Identity
</p>
<div class="org-src-container">
<pre><code class="scala" >append(a, zero) == a
</code></pre>
</div>
<p>
Left Identity
</p>
<div class="org-src-container">
<pre><code class="scala" >append(zero, a) == a
</code></pre>
</div>
<p>
Associativity
</p>
<div class="org-src-container">
<pre><code class="scala" >append(a, append(b, c)) === append(append(a, b), c)
</code></pre>
</div>
</section>
<section id="slide-org8a653cb">
<h4 id="org8a653cb">Option</h4>
<div class="org-src-container">
<pre><code class="scala" >def optionMonoid[A : Monoid] = new Monoid[Option[A]] {
val zero: Int = None
def append(a: Option[A], b: Option[A])) = a match {
case None => b
case Some(x) => b match {
case None => a
case Some(y) => Some(implicitly[Monoid[A]].append(x, y))
}
}
}
optionMonoid[Int].append(Some(3), Some(4)) == Some(7)
optionMonoid[Int].append(Some(3), None) == Some(3)
</code></pre>
</div>
</section>
</section>
<section>
<section id="slide-orgbf502cc">
<h3 id="orgbf502cc">Foldable</h3>
<div class="org-src-container">
<pre><code class="scala" >trait Foldable[F[_]] {
def foldLeft[A, B](a: F[A])(z: B)(f: (B, A) => B): B
def foldRight[A, B](a: F[A])(z: B)(f: (A, B) => B): B
def foldMap[A, B : Monoid](a: F[A])(f: A => B): B =
foldLeft(a)(Monoid[B].empty) { (b, a) =>
Monoid[B].append(b, f(b))
}
}
</code></pre>
</div>
</section>
<section id="slide-orgedc0cd8">
<h4 id="orgedc0cd8">Combine</h4>
<div class="org-src-container">
<pre><code class="scala" >def combine[F[_], A : Monoid](a: F[A]): A =
Foldable[F].foldMap(a)(identity)
combine(List(1, 2, 3, 4)) // 10
combine(List("how", "now", "brown", "cow") // "hownowbrowncow"
</code></pre>
</div>
</section>
<section id="slide-orge227fa8">
<h4 id="orge227fa8">Count</h4>
<div class="org-src-container">
<pre><code class="scala" >def count[F[_], A : Monoid](a: F[A]): A =
Foldable[F].foldMap(a)(_ => 1)
count(Some(4)) // 1
count(None) // 0
count(List(1,2,3,4)) // 4
</code></pre>
</div>
</section>
</section>
<section>
<section id="slide-org1d12ba8">
<h3 id="org1d12ba8">Functor</h3>
<div class="org-src-container">
<pre><code class="scala" >trait Functor[F[_]] {
def map[A, B](a: F[A], f: A => B): F[B]
}
</code></pre>
</div>
</section>
<section id="slide-orgd541c8d">
<h4 id="orgd541c8d">Which means?</h4>
<p>
<code>map</code> allows you to modify the values within a context without modifying the shape of the context
</p>
</section>
<section id="slide-orgc8927ae">
<h4 id="orgc8927ae">What does <i>that</i> mean?</h4>
<div class="org-src-container">
<pre><code class="scala" >Functor[Option].map(Some(4), (_: Int) * 2) === Some(8)
Functor[Option].map(None, (_: Int) * 2) === None
</code></pre>
</div>
<div class="org-src-container">
<pre><code class="scala" >Functor[List].map(List(1, 2, 3, 4), (_: Int) * 2) === List(2, 4, 6, 8)
Functor[List].map(List.empty[Int], (_: Int) * 2) === List()
</code></pre>
</div>
</section>
<section id="slide-org305c1bd">
<h4 id="org305c1bd">Laws</h4>
<p>
Identity
</p>
<div class="org-src-container">
<pre><code class="scala" >F.map(a)(identity) == a
</code></pre>
</div>
<p>
Composition
</p>
<div class="org-src-container">
<pre><code class="scala" >F.map(F.map(a)(f))(g) == F.map(a)(f compose g)
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >a.map(f).map(g) == a.map(f andThen g)
</code></pre>
</div>
</section>
</section>
<section>
<section id="slide-org3ccbd10">
<h3 id="org3ccbd10">Applicative</h3>
<p>
Because not every function has one argument…
</p>
</section>
<section >
<p>
What happens if you have a function
</p>
<div class="org-src-container">
<pre><code class="scala" >f: (A, B) => C
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >Functor[Option].map(Some(3), f)
// error: type mismatch;
// found : (Int, Int) => Int
// required: Int => ?
</code></pre>
</div>
</section>
<section >
<div class="org-src-container">
<pre><code class="scala" >f.curried // (a: Int) => (b: Int) => f(a, b)
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >Functor[Option].map(Some(3), f.curried)
// Some[Int => Int]
</code></pre>
</div>
</section>
<section id="slide-orge39a23b">
<h4 id="orge39a23b">Applicative</h4>
<div class="org-src-container">
<pre><code class="scala" >trait Apply[F[_]] {
def ap[A, B](a: F[A], b: F[A => B]): F[B]
}
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >val sum = (a: Int, b: Int) => a + b
val fOption: Option[Int => Int] = Functor[Option].map(Some(3), sum.curried)
Applicative[Option].ap(Some(4), fOption)
// res4: Option[Int] = Some(7)
Some(4) <*> fOption
</code></pre>
</div>
</section>
<section id="slide-org3d2257b">
<h4 id="org3d2257b">Extensions</h4>
<div class="org-src-container">
<pre><code class="scala" >trait Applicative[F[_]] extends Apply[F] with Functor[F] {
def pure[A](a: A): F[A]
def map2[A, B, C](
a: F[A],
b: F[B],
c: (A, B) => C): F[C] =
ap(b, Fucntor[A].map(a, c.curried))
}
</code></pre>
</div>
</section>
</section>
<section>
<section id="slide-orgdefda8d">
<h3 id="orgdefda8d">Monad</h3>
<div class="outline-text-3" id="text-orgdefda8d">
</div>
</section>
<section id="slide-org0c8e09e">
<h4 id="org0c8e09e">Monad</h4>
<p>
It's really not that scary
</p>
</section>
<section id="slide-orgf963818">
<h4 id="orgf963818">Monad</h4>
<div class="org-src-container">
<pre><code class="scala" >trait Monad[F[_]] extends Applicative[F] {
def flatMap[A, B](a: F[A])(f: A => F[B]): F[B]
}
</code></pre>
</div>
</section>
<section id="slide-orgf01b379">
<h4 id="orgf01b379">Why?</h4>
<div class="org-src-container">
<pre><code class="scala" >def getUser(id: String): Option[User]
def getAddress(user: User): Option[Address]
def getAddressForId(id: Sting) =
getUser(id).flatMap { user =>
getAddress(user)
}
</code></pre>
</div>
<p class="fragment">
This gets ugly really fast.
</p>
</section>
<section id="slide-org8d309c0">
<h4 id="org8d309c0">for-comprehension</h4>
<ul>
<li>Syntactic sugar built into the Scala compiler.</li>
<li>Similar construct (do-notation) exists in Haskell</li>
</ul>
<pre class="example">
def getPOBoxForId(id: String) = for {
user <- getUser(id)
address <- getAddress(user)
pobox <- getPOBox(address)
} yield address
</pre>
</section>
<section id="slide-orgb8cbfff">
<h4 id="orgb8cbfff">Laws</h4>
<p>
Left Identity
</p>
<div class="org-src-container">
<pre><code class="scala" >pure(a).flatMap(f) == f(a)
</code></pre>
</div>
<p>
Right Identity
</p>
<div class="org-src-container">
<pre><code class="scala" >m.flatMap(pure) == m
</code></pre>
</div>
<p>
Associativity
</p>
<div class="org-src-container">
<pre><code class="scala" >flatMap(flatMap(m)(f))(g) == flatMap(m)(x => flatMap(f(x))(g))
</code></pre>
</div>
<div class="org-src-container">
<pre class="fragment"><code class="scala" >(m >>= f) >>= g == m >>= (x => f(x) >>= g)
</code></pre>
</div>
</section>
<section id="slide-orgd580830">
<h4 id="orgd580830">Examples</h4>
<div class="org-src-container">
<pre><code class="scala" >implicit val optionMonad = new Monad[Option] {
def flatMap[A, B](a: Option[A])(f: A => Option[B]) = a match {
case None => None
case Some(x) => f(x)
}
}
</code></pre>
</div>
</section>
</section>
<section>
<section id="slide-org7c3d2cc">
<h3 id="org7c3d2cc">Monads are your friends</h3>
<div class="outline-text-3" id="text-org7c3d2cc">
</div>
</section>
<section id="slide-org27869bc">
<h4 id="org27869bc">Popular Monads</h4>
<ul>
<li>Option</li>
<li>Either</li>
<li>List</li>
</ul>
<ul class="fragment">
<li>But wait! There's more!</li>
</ul>
</section>
<section id="slide-org201968d">
<h4 id="org201968d">Reader</h4>
<div class="org-src-container">
<pre><code class="scala" >Reader[I, A]
I => A
</code></pre>
</div>
</section>
<section id="slide-org95e3a02">
<h4 id="org95e3a02">Writer</h4>
<div class="org-src-container">
<pre><code class="scala" >Writer[A]
A => Unit
</code></pre>
</div>
</section>
<section id="slide-org5bc8f66">
<h4 id="org5bc8f66">State</h4>
<div class="org-src-container">
<pre><code class="scala" >State[S, A]
S => (A, S)
</code></pre>
</div>
</section>
<section id="slide-org84d04e4">
<h4 id="org84d04e4">IO</h4>
<div class="org-src-container">
<pre><code class="scala" >IO[A]
for {
name <- IO { readLine("What is your name?") }
_ <- IO { print(s"Hello, $name") }
} yield ()
</code></pre>
</div>
</section>
<section id="slide-orgf08b209">
<h4 id="orgf08b209">Stream</h4>
<p>
(specifically, <code>fs2.Stream</code>)
</p>
<div class="org-src-container">
<pre><code class="scala" >Stream[F[_], A]
</code></pre>
</div>
<p>
<a href="https://github.com/functional-streams-for-scala/fs2">https://github.com/functional-streams-for-scala/fs2</a>
</p>
</section>
<section id="slide-org209cb07">
<h4 id="org209cb07">Free</h4>
<p class="fragment">
More on this later…
</p>
</section>
</section>
<section>
<section id="slide-orga5ca53e">
<h3 id="orga5ca53e">Additional Resources</h3>
<ul>
<li><a href="https://wiki.haskell.org/Typeclassopedia">Typeclassopedia</a></li>
<li><a href="https://www.manning.com/books/functional-programming-in-scala">Functional Programming in Scala</a></li>
<li><a href="http://learnyouahaskell.com/">Learn You A Haskell For Great Good</a></li>
<li><a href="http://eed3si9n.com/learning-scalaz/index.html">Learning Scalaz</a>/<a href="http://eed3si9n.com/herding-cats/">Herding Cats</a></li>
</ul>
</section>
</section>
<section>
<section id="slide-org318c477">
<h2 id="org318c477">?</h2>
<div class="outline-text-2" id="text-org318c477">
</div>
</section>
</section>
<section>
<section id="slide-org2ced1cc">
<h3 id="org2ced1cc">Thank You!</h3>
<ul>
<li>Bill Carlson</li>
<li><a href="https://twitter.com/coacoas">@coacoas</a></li>
</ul>
</section>
</section>
</div>
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