Allow SPECIALISE pragmas for functions defined in another module

See http://www.haskell.org/pipermail/glasgow-haskell-users/2010-July/019042.html

say I have

  module A where
     class C a where ...
     f :: C a => String -> a

  module B where
     import A
     data T = ...
     instance C T where ...
     g :: String -> SomeOtherType
     g s = doSomethingWith (f s)

Is it possible to SPECIALIZE f for the type T? Currently no.

Some care would be needed to support this. Currently GHC's -fexpose-all-unfoldings makes no attempt to ensure that the exposed unfolding for f is exactly what the user originally wrote. For example, other functions might have been inlined into f's RHS that might make it a lot bigger. Maybe you'd want to say

	{-# SPECIALISABLE f #-}
	f = <blah>

to mean "expose f's unfolding, pretty much as-is, rather than optimising it". This is close to what you get with

	{-# INLINE f #-}

(which also exposes the original RHS) but without the "please inline me at every call site" meaning.

Trac metadata

Trac field	Value
Version	6.12.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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CC	sebf@informatik.uni-kiel.de
Operating system
Architecture