[ ghc-Bugs-1232479 ] panic: "Non-exhaustive patterns in function zip_ty_env"

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Bugs item #1232479, was opened at 2005-07-05 00:39
Message generated for change (Settings changed) made by simonpj
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Category: Compiler (Type checker)
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Simon Peyton Jones (simonpj)
Summary: panic: "Non-exhaustive patterns in function zip_ty_env"

Initial Comment:
ghc-6.4: panic! (the `impossible' happened, GHC version
6.4):
        types/Type.lhs:(1107,0)-(1108,77):
Non-exhaustive patterns in function zip_ty_env

The same file compiles fine with GHC 6.2.2.

Unfortunately I don't have a small example of this
behaviour. I can send you the whole library if you need
it, but it is not painless to get to this point.

It would be great if you could give me some pointers
about where the bug might lie - it uses MPTC instances,
recursive newtypes and the FFI.

thanks,
peter, peteg at unsw.edu.au

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>Comment By: Simon Peyton Jones (simonpj)
Date: 2005-07-06 11:37

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Duplicate of #1202062, fixed in May.

Simon

tc193.hs is a small test:


newtype Signal a = Signal Symbol
newtype Symbol = Symbol (S Symbol)
data S s = Bool Bool
liftl :: Signal a -> Symbol
liftl (Signal a) = a 


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Comment By: Nobody/Anonymous (nobody)
Date: 2005-07-05 01:16

Message:
Logged In: NO 

One more data point: I have a recursive newtype:

newtype P = MkP (ForeignPtr P)

and a couple of renamings:

newtype Q b = MkQ P
newtype R b = MkR P

changing this to:

data Q b = MkQ P
data R b = MkR P

makes things work. I tried cooking up a smaller example
based on this but the bug doesn't appear - it is the
interaction of these newtypes and some other feature, I expect.

Hope this helps.

thanks,
peter

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