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Herbert Valerio Riedel authored
Warn about incoherent/non-canonical 'Applicative'/'Monad' instance declarations. Specifically the following invariants are checked: In 'Monad' instances declarations warn if the any of the following conditions does not hold: * If `return` is overridden it must be canonical (i.e. `return = pure`). * If `(>>)` is overridden it must be canonical (i.e. `(>>) = (*>)`). In 'Applicative' instance declarations: * Warn if 'pure' is defined backwards (i.e. `pure = return`). * Warn if '(*>)' is defined backwards (i.e. `(*>) = (>>)`). NB, this warning flag is not enabled via `-Wall` nor `-Wcompat`. This addresses #11128 Reviewers: quchen, austin, bgamari Reviewed By: bgamari Differential Revision: https://phabricator.haskell.org/D1516
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