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@ -663,7 +668,7 @@ pre > code.sourceCode > span > a:first-child::before { text-decoration: underlin
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<p>Stellen wir uns vor, dass wir eine Funktion schreiben, die einen String bekommt (mehrere Lines mit ACSII-Text) und dieses Wort-für-Wort rückwärts ausgeben soll. Das ist ein einfacher Einzeiler:</p>
|
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<div class="sourceCode" id="cb1"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="kw">module</span> <span class="dt">Main</span> <span class="kw">where</span></span>
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<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb1"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="kw">module</span> <span class="dt">Main</span> <span class="kw">where</span></span>
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<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a></span>
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<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="kw">import</span> <span class="dt">System.Environment</span> (getArgs)</span>
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<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a><span class="kw">import</span> <span class="dt">Data.Monoid</span> (mconcat)</span>
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||||
@ -671,30 +676,30 @@ pre > code.sourceCode > span > a:first-child::before { text-decoration: underlin
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<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a></span>
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||||
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a>main <span class="ot">=</span> <span class="kw">do</span></span>
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<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a> ls <span class="ot"><-</span> <span class="fu">readFile</span> <span class="op">=<<</span> <span class="fu">head</span> <span class="op"><$></span> getArgs</span>
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||||
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a> <span class="fu">mconcat</span> <span class="op"><$></span> <span class="fu">mapM</span> (<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>) (<span class="fu">lines</span> ls) <span class="co">--die eigentliche Funktion, ls ist das argument.</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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||||
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a> <span class="fu">mconcat</span> <span class="op"><$></span> <span class="fu">mapM</span> (<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>) (<span class="fu">lines</span> ls) <span class="co">--die eigentliche Funktion, ls ist das argument.</span></span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
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||||
<p>Was passiert hier an Vodoo? Und was machen die ganzen wilden Zeichen da?</p>
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||||
<p>Gehen wir die Main zeilenweise durch: Wir lesen die Datei, die im ersten Kommandozeilen-Argument gegeben wird. getArgs hat folgende Signatur:</p>
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||||
<div class="sourceCode" id="cb2"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="ot">getArgs ::</span> <span class="dt">IO</span> [<span class="dt">String</span>]</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb2"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="ot">getArgs ::</span> <span class="dt">IO</span> [<span class="dt">String</span>]</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
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||||
<p>Wir bekommen als eine Liste der Argumente. Wir wollen nur das erste. Also machen wir head getArgs. Allerdings fliegt uns dann ein Fehler. head sieht nämlich so aus:</p>
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||||
<div class="sourceCode" id="cb3"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span><span class="ot"> ::</span> [a] <span class="ot">-></span> a</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb3"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span><span class="ot"> ::</span> [a] <span class="ot">-></span> a</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
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||||
<p>Irgendwie müssen wird as <strong>in</strong> das IO bekommen. Hierzu gibt es fmap. Somit ist</p>
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||||
<div class="sourceCode" id="cb4"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="fu">fmap</span><span class="ot"> head ::</span> <span class="dt">IO</span> [a] <span class="ot">-></span> <span class="dt">IO</span> a</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb4"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="fu">fmap</span><span class="ot"> head ::</span> <span class="dt">IO</span> [a] <span class="ot">-></span> <span class="dt">IO</span> a</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
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||||
<p>Ein inline-Alias (um die Funktion links und das Argument rechts zu schreiben und sich ne Menge Klammern zu sparen) ist <$>. Somit ist schlussendlich der Inhalt der Datei aus dem ersten Argument (lazy) in ls.</p>
|
||||
<p>Eine andere Möglichkeit sich das (in diesem Fall) zu merken, bzw. drauf zu kommen ist, dass [] AUCH ein Funktor (sogar eine Monade) ist. Man könnte das also auch so schreiben:</p>
|
||||
<div class="sourceCode" id="cb5"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span><span class="ot"> ::</span> [] a <span class="ot">-></span> a</span>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb5"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span><span class="ot"> ::</span> [] a <span class="ot">-></span> a</span>
|
||||
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span><span class="ot"> ::</span> <span class="dt">Functor</span> f <span class="ot">=></span> [] (f a) <span class="ot">-></span> f a <span class="co">-- das "a" geschickt ersetzt zur Verdeutlichung</span></span>
|
||||
<span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a><span class="ot">getArgs ::</span> <span class="dt">IO</span> [] <span class="dt">String</span></span>
|
||||
<span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a><span class="fu">fmap</span><span class="ot"> head ::</span> <span class="dt">Functor</span> f <span class="ot">=></span> f [] a <span class="ot">-></span> f a</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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||||
<span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a><span class="fu">fmap</span><span class="ot"> head ::</span> <span class="dt">Functor</span> f <span class="ot">=></span> f [] a <span class="ot">-></span> f a</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>fmap “packt” die Funktion quasi 1 Umgebung (Funktor, Monade, ..) weiter rein - Sei es nun in Maybe, Either oder irgendwas anderes.</p>
|
||||
<p>Alternatives (ausführliches) Beispiel am Ende.</p>
|
||||
<p>Wenn wir uns die Signatur ansehen, dann haben wir nun</p>
|
||||
<div class="sourceCode" id="cb6"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span> <span class="op"><$></span><span class="ot"> getArgs ::</span> <span class="dt">IO</span> <span class="dt">String</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb6"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span> <span class="op"><$></span><span class="ot"> getArgs ::</span> <span class="dt">IO</span> <span class="dt">String</span></span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>readFile will aber nun ein String haben. Man kann nun</p>
|
||||
<div class="sourceCode" id="cb7"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a>f <span class="ot"><-</span> <span class="fu">head</span> <span class="op"><$></span> getArgs</span>
|
||||
<span id="cb7-2"><a href="#cb7-2" aria-hidden="true" tabindex="-1"></a>ls <span class="ot"><-</span> <span class="fu">readFile</span> f</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb7"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a>f <span class="ot"><-</span> <span class="fu">head</span> <span class="op"><$></span> getArgs</span>
|
||||
<span id="cb7-2"><a href="#cb7-2" aria-hidden="true" tabindex="-1"></a>ls <span class="ot"><-</span> <span class="fu">readFile</span> f</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>kann man auch “inline” mit =<< die Sachen “auspacken”.</p>
|
||||
<p>Die 2. Zeile lesen wir nun einfach “von hinten”, wie man das meistens tun sollte. Hier ist ein</p>
|
||||
<div class="sourceCode" id="cb8"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a><span class="fu">lines</span><span class="ot"> ls ::</span> [<span class="dt">String</span>]</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb8"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a><span class="fu">lines</span><span class="ot"> ls ::</span> [<span class="dt">String</span>]</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>was uns den Inhalt der Datei zeilenweise gibt. Mit jeder Zeile möchten wir nun folgendes machen:</p>
|
||||
<ol type="1">
|
||||
<li>nach Wörtern trennen (words)</li>
|
||||
@ -703,42 +708,42 @@ pre > code.sourceCode > span > a:first-child::before { text-decoration: underlin
|
||||
<li>diese Zeile ausgeben (putStrLn)</li>
|
||||
</ol>
|
||||
<p>Wenn wir uns die Signatur ansehen:</p>
|
||||
<div class="sourceCode" id="cb9"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a>(<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>)<span class="ot"> ::</span> <span class="dt">String</span> <span class="ot">-></span> <span class="dt">IO</span> ()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb9"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a>(<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>)<span class="ot"> ::</span> <span class="dt">String</span> <span class="ot">-></span> <span class="dt">IO</span> ()</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>Das mag im ersten Moment verwirren, daher noch die Signaturen der Einzelfunktionen:</p>
|
||||
<div class="sourceCode" id="cb10"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a><span class="fu">words</span><span class="ot"> ::</span> <span class="dt">String</span> <span class="ot">-></span> [<span class="dt">String</span>]</span>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb10"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a><span class="fu">words</span><span class="ot"> ::</span> <span class="dt">String</span> <span class="ot">-></span> [<span class="dt">String</span>]</span>
|
||||
<span id="cb10-2"><a href="#cb10-2" aria-hidden="true" tabindex="-1"></a><span class="fu">reverse</span><span class="ot"> ::</span> [a] <span class="ot">-></span> [a]</span>
|
||||
<span id="cb10-3"><a href="#cb10-3" aria-hidden="true" tabindex="-1"></a><span class="fu">unwords</span><span class="ot"> ::</span> [<span class="dt">String</span>] <span class="ot">-></span> <span class="dt">String</span></span>
|
||||
<span id="cb10-4"><a href="#cb10-4" aria-hidden="true" tabindex="-1"></a><span class="fu">putStrLn</span><span class="ot"> ::</span> <span class="dt">String</span> <span class="ot">-></span> <span class="dt">IO</span> ()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<span id="cb10-4"><a href="#cb10-4" aria-hidden="true" tabindex="-1"></a><span class="fu">putStrLn</span><span class="ot"> ::</span> <span class="dt">String</span> <span class="ot">-></span> <span class="dt">IO</span> ()</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>Da wir am Ende in der IO-Monade landen müssen wir das auf unsere Zeilen mit mapM statt map anwenden. Dies sorgt auch dafür, dass die Liste der reihe nach durchgegangen wird. mapM mit unserer Funktion schaut dann so aus:</p>
|
||||
<div class="sourceCode" id="cb11"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true" tabindex="-1"></a><span class="fu">mapM</span> (<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>)<span class="ot"> ::</span> [<span class="dt">String</span>] <span class="ot">-></span> [<span class="dt">IO</span> ()]</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb11"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true" tabindex="-1"></a><span class="fu">mapM</span> (<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>)<span class="ot"> ::</span> [<span class="dt">String</span>] <span class="ot">-></span> [<span class="dt">IO</span> ()]</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>eek! Das [IO ()] sieht ekelig aus. Wir haben eine Liste von IO-gar nichts. Das können wir eigentlich entsorgen. Da wir innerhalb der main-Funktion in einer IO-Monade sind, wollen wir IO () anstatt [IO ()] zurück haben.</p>
|
||||
<p>Wenn wir uns jetzt erinnern, dass [] auch nur eine Monade ist und dass jede Monade ein Monoid ist, dann ist die Lösung einfach. Monoide haben eine “append”-funktion (mappend oder (<>) genannt). Wenn wir “nichts” an “nichts” anhängen, dann erhalten wir …. <em>Trommelwirbel</em> “nichts”! Wir müssen die [IO ()]-Liste also “nur noch” mit mappend falten. Hierzu gibt es schon eine vorgefertigte Funktion:</p>
|
||||
<div class="sourceCode" id="cb12"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb12-1"><a href="#cb12-1" aria-hidden="true" tabindex="-1"></a><span class="fu">mconcat</span><span class="ot"> ::</span> [a] <span class="ot">-></span> a</span>
|
||||
<span id="cb12-2"><a href="#cb12-2" aria-hidden="true" tabindex="-1"></a><span class="fu">mconcat</span> <span class="ot">=</span> <span class="fu">foldr</span> <span class="fu">mappend</span> <span class="fu">mempty</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb12"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb12-1"><a href="#cb12-1" aria-hidden="true" tabindex="-1"></a><span class="fu">mconcat</span><span class="ot"> ::</span> [a] <span class="ot">-></span> a</span>
|
||||
<span id="cb12-2"><a href="#cb12-2" aria-hidden="true" tabindex="-1"></a><span class="fu">mconcat</span> <span class="ot">=</span> <span class="fu">foldr</span> <span class="fu">mappend</span> <span class="fu">mempty</span></span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>Was genau die gewünschte Faltung macht. Wir müssen nun wieder fmap nehmen, da wir die Liste selbst falten wollen - und nicht map, welches auf den IO () innerhalb der Liste arbeiten würde. Durch die Faltung fällt die Liste nun auf IO () zusammen.</p>
|
||||
<p>Viel Voodoo in wenig Code, aber wenn man sich dran gewöhnt hat, sind Monaden in Monaden auch nicht schlimm. Man muss sich immer nur richtig “rein” fmap’en.</p>
|
||||
<hr>
|
||||
<p>Kleinen Tipp gab es noch: mapM_ macht genau das, was oben mit mconcat erreicht werden sollte. Somit kann man auch</p>
|
||||
<div class="sourceCode" id="cb13"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a><span class="fu">mapM_</span> (<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>) (<span class="fu">lines</span> ls)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb13"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a><span class="fu">mapM_</span> (<span class="fu">putStrLn</span> <span class="op">.</span> <span class="fu">unwords</span> <span class="op">.</span> <span class="fu">reverse</span> <span class="op">.</span> <span class="fu">words</span>) (<span class="fu">lines</span> ls)</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>schreiben. Ich hab es aber mal wegen der klarheit oben so gelassen.</p>
|
||||
<section id="alternatives-fmap-beispiel" class="level2">
|
||||
<h2 class="anchored" data-anchor-id="alternatives-fmap-beispiel">Alternatives fmap-Beispiel</h2>
|
||||
<p>Nehmen wir als alternatives Beispiel mal an:</p>
|
||||
<div class="sourceCode" id="cb14"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a><span class="ot">a ::</span> <span class="dt">IO</span> <span class="dt">Maybe</span> <span class="dt">State</span> t</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb14"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a><span class="ot">a ::</span> <span class="dt">IO</span> <span class="dt">Maybe</span> <span class="dt">State</span> t</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>Um Funktionen vom Typ</p>
|
||||
<div class="sourceCode" id="cb15"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb15-1"><a href="#cb15-1" aria-hidden="true" tabindex="-1"></a><span class="ot">f ::</span> <span class="dt">IO</span> a <span class="ot">-></span> <span class="dt">IO</span> a</span>
|
||||
<span id="cb15-2"><a href="#cb15-2" aria-hidden="true" tabindex="-1"></a>f a <span class="co">-- valide</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb15"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb15-1"><a href="#cb15-1" aria-hidden="true" tabindex="-1"></a><span class="ot">f ::</span> <span class="dt">IO</span> a <span class="ot">-></span> <span class="dt">IO</span> a</span>
|
||||
<span id="cb15-2"><a href="#cb15-2" aria-hidden="true" tabindex="-1"></a>f a <span class="co">-- valide</span></span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>zu nehmen, brauchen wir nichts machen. Bei</p>
|
||||
<div class="sourceCode" id="cb16"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a><span class="ot">f' ::</span> <span class="dt">Maybe</span> a <span class="ot">-></span> <span class="dt">Maybe</span> a</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb16"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a><span class="ot">f' ::</span> <span class="dt">Maybe</span> a <span class="ot">-></span> <span class="dt">Maybe</span> a</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>brauchen wir 1 fmap, also ein</p>
|
||||
<div class="sourceCode" id="cb17"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a>f' a <span class="co">-- error</span></span>
|
||||
<span id="cb17-2"><a href="#cb17-2" aria-hidden="true" tabindex="-1"></a>f' <span class="op"><$></span> a</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb17"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a>f' a <span class="co">-- error</span></span>
|
||||
<span id="cb17-2"><a href="#cb17-2" aria-hidden="true" tabindex="-1"></a>f' <span class="op"><$></span> a</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>um eine Funktion</p>
|
||||
<div class="sourceCode" id="cb18"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a><span class="ot">f'' ::</span> <span class="dt">State</span> t <span class="ot">-></span> <span class="dt">State</span> t</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb18"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a><span class="ot">f'' ::</span> <span class="dt">State</span> t <span class="ot">-></span> <span class="dt">State</span> t</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
<p>zu benutzen folglich:</p>
|
||||
<div class="sourceCode" id="cb19"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb19-1"><a href="#cb19-1" aria-hidden="true" tabindex="-1"></a>f'' a <span class="co">-- error</span></span>
|
||||
<div class="code-copy-outer-scaffold"><div class="sourceCode" id="cb19"><pre class="sourceCode haskell code-with-copy"><code class="sourceCode haskell"><span id="cb19-1"><a href="#cb19-1" aria-hidden="true" tabindex="-1"></a>f'' a <span class="co">-- error</span></span>
|
||||
<span id="cb19-2"><a href="#cb19-2" aria-hidden="true" tabindex="-1"></a>f'' <span class="op"><$></span> a <span class="co">-- error</span></span>
|
||||
<span id="cb19-3"><a href="#cb19-3" aria-hidden="true" tabindex="-1"></a><span class="fu">fmap</span> f'' <span class="op"><$></span> a</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
|
||||
<span id="cb19-3"><a href="#cb19-3" aria-hidden="true" tabindex="-1"></a><span class="fu">fmap</span> f'' <span class="op"><$></span> a</span></code></pre></div><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></div>
|
||||
|
||||
|
||||
</section>
|
||||
@ -758,7 +763,7 @@ pre > code.sourceCode > span > a:first-child::before { text-decoration: underlin
|
||||
a.appendChild(i);
|
||||
window.document.body.appendChild(a);
|
||||
}
|
||||
window.setColorSchemeToggle(window.hasAlternateSentinel())
|
||||
setColorSchemeToggle(hasAlternateSentinel())
|
||||
const icon = "";
|
||||
const anchorJS = new window.AnchorJS();
|
||||
anchorJS.options = {
|
||||
|
||||
Reference in New Issue
Block a user