8 lines
420 B
HTML
8 lines
420 B
HTML
<h2 id="composition-problem">Composition problem</h2>
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<p>The Problem; example with lists:</p>
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<pre class="haskell"><code>f x = [x] ⇒ f 1 = [1] ⇒ (f.f) 1 = [[1]] ✗
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g x = [x+1] ⇒ g 1 = [2] ⇒ (g.g) 1 = ERROR [2]+1 ✗
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h x = [x+1,x*3] ⇒ h 1 = [2,3] ⇒ (h.h) 1 = ERROR [2,3]+1 ✗ </code></pre>
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<p>The same problem with most <code>f :: a -> F a</code> functions and functor <code>F</code>.</p>
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