Per the GHC manual section on instance overlap:
If an instance declaration is compiled without
-XOverlappingInstances, then that instance can never be
overlapped. This could perhaps be inconvenient.
It is inconvenient for certain things. If I want to declare a
special `instance Show [MyType] where...` I am out of luck.
However, the solution need not involve a change to the way
instances are handled -- if all the `GHC.*` instances were
compiled with overlapping instances, I'd be able to declare my
instance.
Is there a substantial barrier, either theoretical or
practical, to recompiling GHC this way?
--
_jsn
|...GHC manual section...|
http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-overlap
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