#5458: Phantom types confuse SpecConstr
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.2.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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This program
{{{
type T a = Int
f :: T a -> Bool -> [Int]
f x b = case b of
True -> f x b
False -> x : f x (x > 19)
}}}
gave a Lint error in `SpecConstr` (use -O2). Reason: the specialised
function was abstracted over `x`, but x's type mentions a phantom type
variable `a`, and that ''wasn't'' being abstracted over.
Phantom type variables are a nuisance. A simple fix is to de-synonym the
type of the abstracted variables.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5458>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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