2022-03-12 23:33:26 +00:00
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:PROPERTIES:
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:ID: b22a1c70-02a7-49ce-b5e7-407f1064cd0c
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:END:
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#+title: Semigroup
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2022-03-16 23:56:10 +00:00
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In [[id:9e68d422-cced-4177-96d1-90f777b9a493][Software Development]], a Semigroup is a category of types such that two values
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of the type can be combined associatively to create a new value of the same
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type.
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In [[id:9ac78677-2602-4a06-af0a-4ed82e98a9b6][Haskell]], the function to combine two semigroup values is =mappend=, also
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available as the infix operator =<>=. =mconcat= is also provided for combining a
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list of semigroup values into a single new value. The =mappend= and =mconcat=
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functions are part of the [[id:434ee61c-4461-424f-8dba-5c86ddb06c3c][Monoid]] type class in Haskell, as it was introduced to
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the language prior to Semigroup, and were given those names as the most common
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[[id:434ee61c-4461-424f-8dba-5c86ddb06c3c][Monoid]] is a list.
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#+caption: Semigroup functions in Haskell
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#+begin_src haskell :exports code
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(<>) :: Semigroup a => a -> a -> a
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mappend :: Monoid a => a -> a -> a
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mconcat :: Monoid a => [a] -> a
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#+end_src
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