[ ghc-Bugs-1178851 ] double-panic with GADTs

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Bugs item #1178851, was opened at 2005-04-07 20:39
Message generated for change (Settings changed) made by simonpj
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Category: Compiler (Type checker)
Group: 6.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
>Assigned to: Simon Peyton Jones (simonpj)
Summary: double-panic with GADTs

Initial Comment:
ghc-6.4: panic! (the `impossible' happened, GHC version
6.4):
        cgPanic
    deref{v a1yz}
    static binds for:
    local binds for:
    SRT labelghc-6.4: panic! (the `impossible'
happened, GHC version 6.4):
        initC: srt

Please report it as a compiler bug to
glasgow-haskell-bugs at haskell.org,
or http://sourceforge.net/projects/ghc/.

I've attached a test driver that can reproduce the problem.

-- Esa Pulkkinen <esa.pulkkinen at kotiposti.net>


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Comment By: Nobody/Anonymous (nobody)
Date: 2005-04-12 16:22

Message:
Logged In: NO 

Thank you, this information allowed me to find a workaround.
I need to just use -<< instead of -< for this, and the
problem disappears.

-- Esa Pulkkinen <esa.pulkkinen at kotiposti.net>

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Comment By: Nobody/Anonymous (nobody)
Date: 2005-04-12 10:39

Message:
Logged In: NO 

The short version is a great help.

I think this program should yield a type error. The value of foo
here is a component of the local variable x, and therefore
should
be unavailable to the left of -<.  I've no idea how to
implement it,
though -- presumably a constraint on the free type vars on the
left of -<.

-- Ross

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Comment By: Nobody/Anonymous (nobody)
Date: 2005-04-07 23:00

Message:
Logged In: NO 

Fwiw, here's a trimmed-down version of the above program.

{-# OPTIONS -farrows -fglasgow-exts #-}
class Foo a where foo :: a -> ()
data Bar = forall a. Foo a => Bar a

get :: Bar -> ()
get = proc x -> case x of Bar a -> do foo -< a

-- Thomas Jäger <ThJaeger at gmail.com>


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