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Typeclasses that ONLY define laws. #334

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woparry opened this issue Jun 8, 2015 · 1 comment · Fixed by #1720
Closed

Typeclasses that ONLY define laws. #334

woparry opened this issue Jun 8, 2015 · 1 comment · Fixed by #1720
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@kailuowang

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@woparry
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woparry commented Jun 8, 2015

What do people think of adding typeclasses that only add new laws (ie. have no new functionality, but restrict which implementations are valid.)

I'm specifically thinking of something like CommutativeMonad, which would add a commutativity restriction to Monad (so that e.g. a distributive law can be derived which would allow composition, see #332 and the related discussion re: Traverse).

Since we have discipline, the extra laws can be checked by implementers fairly easily, and it opens up new avenues for writing slightly more general combinators in cats.
@ceedubs
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ceedubs commented Jun 20, 2015

Sounds good to me.

@diesalbla diesalbla mentioned this issue Jun 4, 2017
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@kailuowang kailuowang mentioned this issue Jun 5, 2017
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@kailuowang kailuowang self-assigned this Jun 5, 2017
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type classes with only defined laws to guideline typelevel/cats
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@kailuowang @ceedubs @woparry