panic: funArgTy

The following module crashes GHC 6.11.20090615:

module V where

import GHC.IO.Handle.Types
import GHC.IO.Handle.Internals

f :: Handle -> IO ()
f hdl = withHandle_ "" hdl $ \h -> return h{haDevice=undefined}

results:

$ ghc-testing2 --make V.hs
[1 of 1] Compiling V                ( V.hs, V.o )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 6.11.20090615 for x86_64-unknown-linux):
        funArgTy ghc-prim:GHC.Unit.(){(w) tc 40}

It imports some internals of the IO library; I tried to reproduce it with a completely standalone module, but failed. The field haDevice of Handle__ has existential type - normally GHC rejects a record update when the field has existential type, but does not in this case, I'm not sure why.

Trac metadata

Trac field	Value
Version	6.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture