Constraints should commute over ~
Building the smallcheck package fails with this error:
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)’
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.
Trac metadata
Trac field | Value |
---|---|
Version | 7.10.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |