| SPECIALISE pragmas are not supported in any but the defining module
| because the Core for a function to specialise is not guaranteed to be
| available in any other module. I don't think there is any other
| barrier.
Yes, exactly.
| It is possible to imagine implementing a remedy for this by using
| -fexpose-all-unfoldings and having GHC use the exposed Core to
| generate a specialisation in any importing module.
Indeed, I've often thought of such a feature. It would be a Good Thing.
But some care would be needed. 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. Hmm. Oh if I had more time.
But as of today, no it just isn't supported. Another ticket!
http://hackage.haskell.org/trac/ghc/ticket/4227
Simon
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