19 lines
708 B
Markdown
19 lines
708 B
Markdown
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κατα-morphism: fold generalization
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----------------------------------
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`acc` type of the "accumulator":
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`fold :: (acc -> a -> acc) -> acc -> [a] -> acc`
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Idea: put the accumulated value inside the type.
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<pre class="haskell"><code>-- Equivalent to fold (+1) 0 "cata"
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(Cons 'c' (Cons 'a' (Cons 't' (Cons 'a' Nil))))
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(Cons 'c' (Cons 'a' (Cons 't' (Cons 'a' <span style="border: solid 1px;">0</span>))))
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(Cons 'c' (Cons 'a' (Cons 't' <span style="border: solid 1px;">1</span>)))
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(Cons 'c' (Cons 'a' <span style="border: solid 1px;">2</span>))
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(Cons 'c' <span style="border: solid 1px;">3</span>)
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<span style="border: solid 1px;">4</span></code></pre>
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But where are all the informations? `(+1)` and `0`?
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