#4846: Newtype derving used wrongly
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Emil Axelsson reports: I attach a program `Test.hs` which I suspect
demonstrates a bug in GHC. The important lines are:
{{{
showType :: forall a . Expr a -> String
showType (Lit _) = show (typeOf (undefined :: a))
test1 = showType (mk :: Expr BOOL) -- Prints "Bool" (wrong?)
test2 = showType (Lit mk :: Expr BOOL) -- Prints "Main.BOOL" (correct)
}}}
`test1` and `test2` give different results, even though showType shouldn't
be able to tell them apart. It seems that the `Typeable` context packed
with the Lit constructor is wrong in `test2`.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4846>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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