Locally-scoped RULES
I'd like the following to compile:
module A where
f = g where
{-# RULES "g/h" g = h #-}
g = undefined
h = undefined
This doesn't currently compile, because all RULES have to be top-level.
However, GHC permits SPECIALISE pragmas at local scope; the following compiles:
module Test where
f :: Num a => a -> a
f = g where
{-# SPECIALISE g :: Int -> Int #-}
g :: Num b => b -> b
g x = x + x
(Admittedly, this example discards the specialisation, but more interesting examples don't.)
I only point out that the SPECIALISE pragma succeeds, because the user manual has the comment that rules subsume the 'Obsolete SPECIALIZE syntax', but in this case they don't.
I've got a real example where I would like locally-scoped RULES, but it is rather long, so I will post it as a comment.
Trac metadata
Trac field | Value |
---|---|
Version | 7.0.3 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
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Blocking | |
CC | |
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Architecture |