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An Introduction to Scala.html
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<title>An Introduction to Scala</title>
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<div class="slides">
<div class="slide-wrapper">
<div class="slide" id="slide-1">
<div data-id="1" class="slide-overlay"></div>
<section class="slide-content"><h1 id="scala">Scala</h1>
<h2 id="a-general-purpose-programming-language-providing-support-for-functional-programming-and-a-strong-static-type-system-">A general-purpose programming language providing support for functional programming and a strong static type system.</h2>
</section>
</div>
</div>
<div class="slide-wrapper">
<div class="slide hidden" id="slide-2">
<div data-id="2" class="slide-overlay"></div>
<section class="slide-content"><h3 id="scala-in-a-nutshell">Scala in a Nutshell</h3>
<ul>
<li>Seamless Java Interop</li>
<li>Type Inference</li>
<li>Concurrency & Distribution</li>
<li>Traits</li>
<li>Pattern Matching</li>
<li>Higher-order functions</li>
</ul>
</section>
</div>
</div>
<div class="slide-wrapper">
<div class="slide hidden" id="slide-3">
<div data-id="3" class="slide-overlay"></div>
<section class="slide-content"><h3 id="building-tools">Building Tools</h3>
<ul>
<li><p>sbt</p>
<p> You can download it from <a href="https://www.scala-sbt.org/">https://www.scala-sbt.org/</a> .</p>
</li>
<li><p>maven</p>
<p> If you want to compile with Java, maven is suggested.</p>
</li>
</ul>
</section>
</div>
</div>
<div class="slide-wrapper">
<div class="slide hidden" id="slide-4">
<div data-id="4" class="slide-overlay"></div>
<section class="slide-content"><h3 id="building-tools">Building Tools</h3>
<ul>
<li>recommended source management with sbt<pre><code>project/
plugins.sbt
build.properties
src/
main/
resources/
scala/
java/
test/
resources
scala/
java/
build.sbt
</code></pre></li>
</ul>
</section>
</div>
</div>
<div class="slide-wrapper">
<div class="slide hidden" id="slide-5">
<div data-id="5" class="slide-overlay"></div>
<section class="slide-content"><h3 id="building-tools">Building Tools</h3>
<ul>
<li><p>an example of <code>build.sbt</code></p>
<pre><code class="lang-scala"> <span class="hljs-type">ThisBuild</span> / scalaVersion := <span class="hljs-string">"2.12.6"</span>
<span class="hljs-type">ThisBuild</span> / organization := <span class="hljs-string">"com.example"</span>
<span class="hljs-keyword">lazy</span> <span class="hljs-keyword">val</span> hello = (project in file(<span class="hljs-string">"."</span>))
.settings(
name := <span class="hljs-string">"Hello"</span>,
libraryDependencies += <span class="hljs-string">"org.scalatest"</span> %% <span class="hljs-string">"scalatest"</span> % <span class="hljs-string">"3.0.5"</span> % <span class="hljs-type">Test</span>,
)
</code></pre>
</li>
</ul>
</section>
</div>
</div>
<div class="slide-wrapper">
<div class="slide hidden" id="slide-6">
<div data-id="6" class="slide-overlay"></div>
<section class="slide-content"><h3 id="building-tools">Building Tools</h3>
<ul>
<li>sbt commands<ul>
<li>clean</li>
<li>compile</li>
<li>test</li>
<li>console</li>
<li>...</li>
</ul>
</li>
</ul>
</section>
</div>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li><p>Hello World</p>
<pre><code class="lang-scala"> <span class="hljs-class"><span class="hljs-keyword">object</span> <span class="hljs-title">Main</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span></span>(args: <span class="hljs-type">Array</span>[<span class="hljs-type">String</span>]): <span class="hljs-type">Unit</span> =
println(<span class="hljs-string">"Hello, Scala developer!"</span>)
}
</code></pre>
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</ul>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li><code>val</code> <code>var</code> <code>lazy</code></li>
<li><code>def fun[T](x:A,y:B):C = expr</code></li>
<li><code>(x:A,y:B) => expr</code></li>
<li><code>{expr}</code> = <code>expr</code></li>
<li><code>match x {case _=>expr}</code></li>
<li><code>new X</code></li>
<li><code>x.fun(y)</code> = <code>x fun y</code></li>
<li><code>;</code> and <code>return</code></li>
</ul>
</section>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li><code>package</code> <code>import</code></li>
<li><code>class A[T](x:T){}</code></li>
<li><code>case class B(x:A[C])</code></li>
<li><code>extend</code> <code>with</code></li>
<li><code>object</code></li>
<li><code>trait</code></li>
</ul>
</section>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li><p><code>apply</code> : the factory function</p>
<pre><code class="lang-scala"> <span class="hljs-type">List</span>(
<span class="hljs-string">"a string"</span>,
<span class="hljs-number">732</span>, <span class="hljs-comment">// an integer</span>
'c', <span class="hljs-comment">// a character</span>
<span class="hljs-literal">true</span>, <span class="hljs-comment">// a boolean value</span>
() => <span class="hljs-string">"an anonymous function returning a string"</span>
)
</code></pre>
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</ul>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li><p>currying</p>
<pre><code class="lang-scala"> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">foldLeft</span></span>[<span class="hljs-type">B</span>](z: <span class="hljs-type">B</span>)(op: (<span class="hljs-type">B</span>, <span class="hljs-type">A</span>) => <span class="hljs-type">B</span>): <span class="hljs-type">B</span>
<span class="hljs-keyword">val</span> numbers = <span class="hljs-type">List</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>, <span class="hljs-number">8</span>, <span class="hljs-number">9</span>, <span class="hljs-number">10</span>)
<span class="hljs-keyword">val</span> res = numbers.foldLeft(<span class="hljs-number">0</span>)((m, n) => m + n)
print(res) <span class="hljs-comment">// 55</span>
</code></pre>
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</ul>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li><p><code>_</code></p>
<pre><code class="lang-scala"> numbers.foldLeft(<span class="hljs-number">0</span>, {(m: <span class="hljs-type">Int</span>, n: <span class="hljs-type">Int</span>) => m + n})
numbers.foldLeft(<span class="hljs-number">0</span>)(_+_)
</code></pre>
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</ul>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li><p>monad</p>
<pre><code class="lang-scala"> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">flatMap</span></span>[<span class="hljs-type">B</span>](f: (<span class="hljs-type">A</span>) => <span class="hljs-type">GenTraversableOnce</span>[<span class="hljs-type">B</span>]): <span class="hljs-type">TraversableOnce</span>[<span class="hljs-type">B</span>]
<span class="hljs-keyword">for</span>(x<-<span class="hljs-type">M</span>) <span class="hljs-keyword">yield</span> y
</code></pre>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li>variances<pre><code class="lang-scala"> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Foo</span>[+<span class="hljs-type">A</span>] <span class="hljs-title">//</span> <span class="hljs-title">A</span> <span class="hljs-title">covariant</span> <span class="hljs-title">class</span></span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Bar</span>[-<span class="hljs-type">A</span>] <span class="hljs-title">//</span> <span class="hljs-title">A</span> <span class="hljs-title">contravariant</span> <span class="hljs-title">class</span></span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Baz</span>[<span class="hljs-type">A</span>] <span class="hljs-title">//</span> <span class="hljs-title">An</span> <span class="hljs-title">invariant</span> <span class="hljs-title">class</span></span>
</code></pre>
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</ul>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li>lower && upper bound<pre><code class="lang-scala"> <span class="hljs-class"><span class="hljs-keyword">trait</span> <span class="hljs-title">Node</span>[+<span class="hljs-type">B</span>] </span>{
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">prepend</span></span>[<span class="hljs-type">U</span> >: <span class="hljs-type">B</span>](elem: <span class="hljs-type">U</span>): <span class="hljs-type">Node</span>[<span class="hljs-type">U</span>]
}
<span class="hljs-keyword">case</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">ListNode</span>[+<span class="hljs-type">B</span>](<span class="hljs-params">h: <span class="hljs-type">B</span>, t: <span class="hljs-type">Node</span>[<span class="hljs-type">B</span>]</span>) <span class="hljs-keyword">extends</span> <span class="hljs-title">Node</span>[<span class="hljs-type">B</span>] </span>{
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">prepend</span></span>[<span class="hljs-type">U</span> >: <span class="hljs-type">B</span>](elem: <span class="hljs-type">U</span>): <span class="hljs-type">ListNode</span>[<span class="hljs-type">U</span>] = <span class="hljs-type">ListNode</span>(elem, <span class="hljs-keyword">this</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">head</span></span>: <span class="hljs-type">B</span> = h
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">tail</span></span>: <span class="hljs-type">Node</span>[<span class="hljs-type">B</span>] = t
}
</code></pre>
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<section class="slide-content"><pre><code class="lang-scala"> <span class="hljs-keyword">case</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Nil</span>[+<span class="hljs-type">B</span>](<span class="hljs-params"></span>) <span class="hljs-keyword">extends</span> <span class="hljs-title">Node</span>[<span class="hljs-type">B</span>] </span>{
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">prepend</span></span>[<span class="hljs-type">U</span> >: <span class="hljs-type">B</span>](elem: <span class="hljs-type">U</span>): <span class="hljs-type">ListNode</span>[<span class="hljs-type">U</span>] = <span class="hljs-type">ListNode</span>(elem, <span class="hljs-keyword">this</span>)
}
</code></pre>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li>compound type<pre><code class="lang-scala"> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">cloneAndReset</span></span>(obj: <span class="hljs-type">Cloneable</span> <span class="hljs-keyword">with</span> <span class="hljs-type">Resetable</span>): <span class="hljs-type">Cloneable</span> = {
<span class="hljs-comment">//...</span>
}
</code></pre>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li>implicit parameters<pre><code class="lang-scala"> <span class="hljs-keyword">abstract</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Monoid</span>[<span class="hljs-type">A</span>] </span>{
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span></span>(x: <span class="hljs-type">A</span>, y: <span class="hljs-type">A</span>): <span class="hljs-type">A</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">unit</span></span>: <span class="hljs-type">A</span>
}
<span class="hljs-class"><span class="hljs-keyword">object</span> <span class="hljs-title">ImplicitTest</span> </span>{
<span class="hljs-keyword">implicit</span> <span class="hljs-keyword">val</span> stringMonoid: <span class="hljs-type">Monoid</span>[<span class="hljs-type">String</span>] = <span class="hljs-keyword">new</span> <span class="hljs-type">Monoid</span>[<span class="hljs-type">String</span>] {
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span></span>(x: <span class="hljs-type">String</span>, y: <span class="hljs-type">String</span>): <span class="hljs-type">String</span> = x concat y
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">unit</span></span>: <span class="hljs-type">String</span> = <span class="hljs-string">""</span>
}
</code></pre>
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</ul>
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<section class="slide-content"><pre><code class="lang-scala"> <span class="hljs-keyword">implicit</span> <span class="hljs-keyword">val</span> intMonoid: <span class="hljs-type">Monoid</span>[<span class="hljs-type">Int</span>] = <span class="hljs-keyword">new</span> <span class="hljs-type">Monoid</span>[<span class="hljs-type">Int</span>] {
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span></span>(x: <span class="hljs-type">Int</span>, y: <span class="hljs-type">Int</span>): <span class="hljs-type">Int</span> = x + y
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">unit</span></span>: <span class="hljs-type">Int</span> = <span class="hljs-number">0</span>
}
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">sum</span></span>[<span class="hljs-type">A</span>](xs: <span class="hljs-type">List</span>[<span class="hljs-type">A</span>])(<span class="hljs-keyword">implicit</span> m: <span class="hljs-type">Monoid</span>[<span class="hljs-type">A</span>]): <span class="hljs-type">A</span> =
<span class="hljs-keyword">if</span> (xs.isEmpty) m.unit
<span class="hljs-keyword">else</span> m.add(xs.head, sum(xs.tail))
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span></span>(args: <span class="hljs-type">Array</span>[<span class="hljs-type">String</span>]): <span class="hljs-type">Unit</span> = {
println(sum(<span class="hljs-type">List</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>))) <span class="hljs-comment">// uses IntMonoid implicitly</span>
println(sum(<span class="hljs-type">List</span>(<span class="hljs-string">"a"</span>, <span class="hljs-string">"b"</span>, <span class="hljs-string">"c"</span>))) <span class="hljs-comment">// uses StringMonoid implicitly</span>
}
}
</code></pre>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li>by-name parameters<pre><code class="lang-scala"> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">calculate</span></span>(input: => <span class="hljs-type">Int</span>) = input * <span class="hljs-number">37</span>
</code></pre>
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<section class="slide-content"><h3 id="the-syntax-of-scala">The Syntax of Scala</h3>
<ul>
<li>adt in scala<pre><code class="lang-scala"> <span class="hljs-keyword">sealed</span> <span class="hljs-class"><span class="hljs-keyword">trait</span> <span class="hljs-title">Tree</span>[<span class="hljs-type">T</span>]</span>
<span class="hljs-keyword">case</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Node</span>[<span class="hljs-type">T</span>](<span class="hljs-params">left: <span class="hljs-type">Tree</span>[<span class="hljs-type">T</span>], right: <span class="hljs-type">Tree</span>[<span class="hljs-type">T</span>]</span>) <span class="hljs-keyword">extends</span> <span class="hljs-title">Tree</span>[<span class="hljs-type">T</span>]</span>
<span class="hljs-keyword">case</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Leaf</span>[<span class="hljs-type">T</span>](<span class="hljs-params">value: <span class="hljs-type">T</span></span>) <span class="hljs-keyword">extends</span> <span class="hljs-title">Tree</span>[<span class="hljs-type">T</span>]</span>
</code></pre>
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<section class="slide-content"><h3 id="the-scala-libraries">The Scala Libraries</h3>
<ul>
<li><p>regex</p>
<pre><code class="lang-scala"> <span class="hljs-keyword">import</span> scala.util.matching.<span class="hljs-type">Regex</span>
<span class="hljs-keyword">val</span> numberPattern: <span class="hljs-type">Regex</span> = <span class="hljs-string">"[0-9]"</span>.r
numberPattern.findFirstMatchIn(<span class="hljs-string">"awesomepassword"</span>) <span class="hljs-keyword">match</span> {
<span class="hljs-keyword">case</span> <span class="hljs-type">Some</span>(_) => println(<span class="hljs-string">"Password OK"</span>)
<span class="hljs-keyword">case</span> <span class="hljs-type">None</span> => println(<span class="hljs-string">"Password must contain a number"</span>)
}
</code></pre>
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<section class="slide-content"><h3 id="the-scala-libraries">The Scala Libraries</h3>
<ul>
<li>collections<pre><code class="lang-scala"> <span class="hljs-keyword">val</span> seq = <span class="hljs-type">Seq</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
<span class="hljs-keyword">val</span> set = <span class="hljs-type">Set</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
<span class="hljs-keyword">val</span> map = <span class="hljs-type">Map</span>(<span class="hljs-number">1</span> -> <span class="hljs-string">"one"</span>, <span class="hljs-number">2</span> -> <span class="hljs-string">"two"</span>, <span class="hljs-number">3</span> -> <span class="hljs-string">"three"</span>)
</code></pre>
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<section class="slide-content"><pre><code class="lang-scala"> <span class="hljs-keyword">val</span> votes = <span class="hljs-type">Seq</span>((<span class="hljs-string">"scala"</span>, <span class="hljs-number">1</span>), (<span class="hljs-string">"java"</span>, <span class="hljs-number">4</span>), (<span class="hljs-string">"scala"</span>, <span class="hljs-number">10</span>), (<span class="hljs-string">"scala"</span>, <span class="hljs-number">1</span>), (<span class="hljs-string">"python"</span>, <span class="hljs-number">10</span>))
<span class="hljs-keyword">val</span> orderedVotes = votes
.groupBy(_._1)
.map { <span class="hljs-keyword">case</span> (which, counts) =>
(which, counts.foldLeft(<span class="hljs-number">0</span>)(_ + _._2))
}.toSeq
.sortBy(_._2)
.reverse
</code></pre>
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