Opened 3 years ago

Closed 3 years ago

#10499 closed bug (duplicate)

Constraints should commute over ~

Reported by: joelteon Owned by:
Priority: normal Milestone:
Component: Compiler Version: 7.10.1
Keywords: Cc:
Operating System: Unknown/Multiple Architecture: Unknown/Multiple
Type of failure: None/Unknown Test Case:
Blocked By: Blocking:
Related Tickets: Differential Rev(s):
Wiki Page:


Building the smallcheck package fails with this error:

    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)’

Wondering if this is a bug in 7.11's constraint solver or 7.10's, since 7.10 and previous GHCs accept it and 7.11 doesn't.

Change History (2)

comment:1 Changed 3 years ago by joelteon

Summary: Constraints should associate over ~Constraints should commute over ~

comment:2 Changed 3 years ago by goldfire

Resolution: duplicate
Status: newclosed

Fixed as #10423. Thanks for reporting!

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