#3150: Overlapping data instances can segfault
-----------------------------+----------------------------------------------
Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.10.1 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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When exploring data families for some fast unboxed tuple representation,
we came across the following scenario.
{{{
class Foo a where
data Bar a :: *
instance Foo a where
data Bar a = PBar a
instance Foo () where
data Bar () = PUnit
}}}
{{{
GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main ( Foo.hs, interpreted )
Ok, modules loaded: Main.
*Main> case PUnit of PBar x -> x
Segmentation fault
}}}
It appears the compiler is allowing the refinement of a into () because
they overlap, when it shouldn't.
This is less academic than this example, because it affects doing similar
operations to automatically unbox tuples of primitives when possible.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3150>
GHC <http://www.haskell.org/ghc/>
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