2022-03-12 23:33:26 +00:00
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:PROPERTIES:
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:ID: 434ee61c-4461-424f-8dba-5c86ddb06c3c
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:END:
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#+title: Monoid
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A [[id:b22a1c70-02a7-49ce-b5e7-407f1064cd0c][Semigroup]] with an identity value.
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2022-03-16 23:56:10 +00:00
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In [[id:9ac78677-2602-4a06-af0a-4ed82e98a9b6][Haskell]], the function representing the identity value for a given Monoid is
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=mempty=.
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#+caption: =mempty= in Haskell
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#+begin_src haskell :exports code
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mempty :: Monoid a => a
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#+end_src
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2022-03-12 23:33:26 +00:00
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* Examples
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2022-03-16 23:56:10 +00:00
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** List
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Combined with =append=, identity value is the empty list (=[]=)
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** Number Addition
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Combined with =+=, identity value is =0=
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** Number Multiplication
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Combined with =*=, identity value is =1=
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