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Result is not a lawful Monad #147

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benjamin-hodgson opened this issue Aug 5, 2017 · 0 comments
Open

Result is not a lawful Monad #147

benjamin-hodgson opened this issue Aug 5, 2017 · 0 comments

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@benjamin-hodgson
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benjamin-hodgson commented Aug 5, 2017 •
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Result's Monad instance violates the (<*>) = ap law.

ghci> Error "a" `ap` Error "b"
Error "a"
ghci> Error "a" <*> Error "b"
Error "ab"

This is a potential "gotcha" and it should at least be documented.
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