The impossible happened, code commented

initializeWorld = (\w -> do
		worldSetGravity w 0 (-1.0) 0
		worldSetERP w 0.2
		worldSetCFM w 1e-5
		worldSetContactMaxCorrectingVel w 0.9
		worldSetContactSurfaceLayer w 0.001
		worldSetAutoDisableFlag w 1),

these worldSet* functions are unsafe FFI calls. initializeWorld is Ptr Int -> IO ()

commenting this prevents this bug. this code is found in a top level declaration:

initiailLevel = Level {
 ...
}

of which contains the record for initializeWorld

changed milestone to %6.6.1

changed weight to 5

added Tbug Trac import labels

changed the description

You need to give us a few more clues! For example, the error message you get.

But for this one we'll probably need to be able to reproduce your problem. Can you make a small program that demonstrates it? Thanks

Simon

More clues found during investigation (use ODE library if needed):

foreign import ccall unsafe "dWorldSetContactSurfaceLayer" worldSetContactSurfaceLayer :: WorldID -> Real -> IO ()

type WorldID = Int type Real = Double

initializeWorld = (\w -> do --worldSetGravity w 0 (-1.0) 0 --worldSetERP w 0.2 --worldSetCFM w 1e-5 --worldSetContactMaxCorrectingVel w 0.9 worldSetContactSurfaceLayer w 0.001 ), --worldSetAutoDisableFlag w 1),

--- now here is the:

ghc-6.6: panic! (the 'impossible' happened)

(GHC version 6.6 for i386-apple-darwin):

lookupDeprec base:GHC.Real.fromRational{v 01G}

-- Then change worldSetContactSurfaceLayer's second argument to 1.0 .... bug disappears.

I hope this helps

Attached file imp.tar.bz2 (download).

Contains standalone compilable demonstrating issues with the above, the "impossible bug" which seems to relate to rational literals, has spread further from logic recently.

Confirmed to be caused by -fno-implicit-prelude when compiling this file (Level.hs in the attachment file) with ghc --make.

mentioned in commit e975c8f0

mentioned in commit f0022b77

This is a plain bug in the type checker. The program should clearly be rejected. I've fixed the bug.

MERGE to 6.6.1 branch

Tue Feb 6 16:54:56 GMT 2007 simonpj@microsoft.com

• Check for escape when unifying forall-types

Simon

Trac metadata

Trac field	Value
Type	Bug → MergeReq
Test case	→ tcfail174

Bother. IGNORE my last comment; it was intended for a different bug entirely. Sorry.

Simon

Trac metadata

Trac field	Value
Type	MergeReq → Bug
Test case	tcfail174 →

I've just compiled the file you sent (on Unix) with GHC 6.6, thus:

  ghc --make -fno-implicit-prelude Level.hs

It worked fine. Can you help us reproduce this? Send the exact command line, and output you get. Pls start from a clean directory with precisely the download that you attached to this bug report.

Thanks

Simon

changed title from The impossible happened, code commented to [unreproducible] The impossible happened, code commented

changed weight to 0

I also can't reproduce this. Does anyone have any more info?

Trac metadata

Trac field	Value
Priority	normal → lowest

changed title from [unreproducible] The impossible happened, code commented to The impossible happened, code commented

I attach ghc_trac_1128_imp2.tar.gz (a slightly modified imp.tar.bz2) that PPC Mac OS X 10.4 reacts to as follows:

Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base thorkilnaur$ gunzip ghc_trac_1128_imp2.tar.gz
Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base thorkilnaur$ mkdir verify
Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base thorkilnaur$ cd verify
Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base/verify thorkilnaur$ tar xvf ../ghc_trac_1128_imp2.tar
ghc_trac_1128_imp2/
ghc_trac_1128_imp2/cbits.c
ghc_trac_1128_imp2/Level.hs
ghc_trac_1128_imp2/Math.hs
ghc_trac_1128_imp2/ODE.hs
Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base/verify thorkilnaur$ diff ../imp/ ghc_trac_1128_imp2/
diff ../imp/Level.hs ghc_trac_1128_imp2/Level.hs
28a29,30
>       initializeWorld :: WorldID->IO (),
> 
45d46
< {-
53d53
< -}
Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base/verify thorkilnaur$ cd ghc_trac_1128_imp2
Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base/verify/ghc_trac_1128_imp2 thorkilnaur$ ghc --make -fno-implicit-prelude Level.hs
[1 of 3] Compiling ODE              ( ODE.hs, ODE.o )
[2 of 3] Compiling Math             ( Math.hs, Math.o )
[3 of 3] Compiling Level            ( Level.hs, Level.o )
ghc-6.7.20070209: panic! (the 'impossible' happened)
  (GHC version 6.7.20070209 for powerpc-apple-darwin):
        lookupDeprec base:GHC.Real.fromRational{v 01G}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Thorkil-Naurs-Computer:~/tn/GHC/trac/1128/base/verify/ghc_trac_1128_imp2 thorkilnaur$ 

This happens every time I try. So I have taken the liberty of removing the [unreproducible]-part of the summary.

Attached file ghc_trac_1128_imp2.tar.gz (download).

Modified imp.tar.bz2 that reproduces the problem for me

mentioned in commit 60ce42c5

mentioned in commit 1e9a9216

OK, I've nailed this one. Thank you for the bug report.

An easy workaround is to use -fno-warn-deprecations for this module.

Simon

Trac metadata

Trac field	Value
Type	Bug → MergeReq
Test case	→ rn051

closed

Merged.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

Trac metadata

Trac field	Value
Architecture	Unknown → Unknown/Multiple

Trac metadata

Trac field	Value
Operating system	Unknown → Unknown/Multiple

added Plow label