#7453: unsafe coerce without extensions
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type
checker)
Version: 7.6.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: GHC accepts invalid program | Blockedby:
Blocking: | Related:
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The following program implements an unsafe coerce and works on versions of
GHC at least as far back as 7.0.3 but is fixed in HEAD. I'm reporting this
because I don't know if it was fixed on purpose and might merit at least a
fix to the 7.6.X branch if not the 7.4.X branch (due to its use in the
platform)
{{{
newtype Id a = Id { runId :: a }
-- Providing this type triggers a type-error
-- cast :: a -> b
cast v = runId z
where
z :: Id v
z = aux
where
aux = Id v
}}}
Example usage:
{{{
*Main> map cast [97..107 :: Int] :: String
"abcdefghijk"
*Main> cast (Just True) :: String
"\-1152921504589708267Segmentation fault: 11
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7453>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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