Optimiser bug with extistentials and GADT's
Given the program:
{-# LANGUAGE GADTs, ExistentialQuantification #-}
module GadtBug(bug) where
data Existential = forall a . Existential (Gadt a)
data Gadt a where Value :: Gadt Double
bug = [ match undefined | ps <- undefined, _ <- ps ]
where
match (Existential _) = undefined
match (Existential _) = undefined
Using GHC Head from yesterday, compiling without optimisations I get:
C:\Neil>ghc --make GadtBug.hs
[1 of 1] Compiling GadtBug ( GadtBug.hs, GadtBug.o )
GadtBug.hs:11:8:
Warning: Pattern match(es) are overlapped
In the definition of `match': match (Existential _) = ...
With optimisations (-O or -O2) I get:
C:\Neil\paradise-bug-csdg\alone>ghc --make GadtBug.hs -O
[1 of 1] Compiling GadtBug ( GadtBug.hs, GadtBug.o )
GadtBug.hs:11:8:
Warning: Pattern match(es) are overlapped
In the definition of `match': match (Existential _) = ...
ghc: panic! (the 'impossible' happened)
(GHC version 6.9.20080905 for i386-unknown-mingw32):
idInfo a{tv ag4} [sk]
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
-- Neil
Trac metadata
Trac field | Value |
---|---|
Version | 6.9 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | Unknown |
Architecture | Unknown |