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Can't infer Monad n from (Monad m, m ~ n)

This looks like a regression in GHC HEAD.

Test/SmallCheck/Property.hs:187:10:
    Could not deduce (Monad n)
      arising from the superclasses of an instance declaration
    from the context: (Monad m, m ~ n)
      bound by the instance declaration
      at Test/SmallCheck/Property.hs:187:10-52
    Possible fix:
      add (Monad n) to the context of the instance declaration
    In the instance declaration for ‘Testable n (Property m)’

The code is here: https://github.com/feuerbach/smallcheck/blob/v1.1.1/Test/SmallCheck/Property.hs#L187-L188

Originally reported here: https://github.com/feuerbach/smallcheck/issues/28

Trac metadata
Trac field Value
Version 7.11
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
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