id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
6013,the 'impossible' happened,tlvb,,"Please forgive me if this is a duplicate or irrelevant, bug reporting and Haskell are two things I work with seldom enough that I cannot be considered good at either, but as what happened should be 'impossible' I thought I'd at least give you a heads up. I tried looking for similar bugs, but I do not really know what I would be looking for...

GHCi (newly opened, -v flag):
{{{
[leo@derse brutelift]$ ghci -v
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Glasgow Haskell Compiler, Version 7.4.1, stage 2 booted by GHC version 7.4.1
Using binary package database: /usr/lib/ghc-7.4.1/package.conf.d/package.cache
wired-in package ghc-prim mapped to ghc-prim-0.2.0.0-c2ff696e5b8ec4d4b2bc2e42085fe471
wired-in package integer-gmp mapped to integer-gmp-0.4.0.0-3cccac07aef8e27023f605c1f45bdf74
wired-in package base mapped to base-4.5.0.0-40b99d05fae6a4eea95ea69e6e0c9702
wired-in package rts mapped to builtin_rts
wired-in package template-haskell mapped to template-haskell-2.7.0.0-8c8cd20e21666657195efabced685fe1
wired-in package dph-seq not found.
wired-in package dph-par not found.
Hsc static flags: -static
Loading package ghc-prim ... linking ... done.
*** gcc:
'/usr/bin/gcc' '-fno-stack-protector' '-Wl,--hash-size=31' '-Wl,--reduce-memory-overheads' '-L/usr/lib/ghc-7.4.1/integer-gmp-0.4.0.0' '--print-file-name' 'libgmp.so'
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :load brutelift
*** Chasing dependencies:
Chasing modules from: 
Stable obj: []
Stable BCO: []
unload: retaining objs []
unload: retaining bcos []
Ready for upsweep []
Upsweep completely successful.
*** Deleting temp files:
Deleting: 
*** Chasing dependencies:
Chasing modules from: *brutelift.hs
Stable obj: []
Stable BCO: []
unload: retaining objs []
unload: retaining bcos []
Ready for upsweep
  [NONREC
      ModSummary {
         ms_hs_date = Tue Apr 17 18:10:32 CEST 2012
         ms_mod = main:Main,
         ms_textual_imps = [import (implicit) Prelude, import Data.List]
         ms_srcimps = []
      }]
*** Deleting temp files:
Deleting: 
compile: input file brutelift.hs
Created temporary directory: /tmp/ghc5399_0
*** Checking old interface for main:Main:
[1 of 1] Compiling Main             ( brutelift.hs, interpreted )
*** Parser:
*** Renamer/typechecker:
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.1 for x86_64-unknown-linux):
	nameModule show{tv abQ}

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

>
}}}

brutelift.hs:

{{{
import Data.List

data Transfer = Load | Unload
data Action = Left Transfer Int | Right Transfer Int

data BlockDispersion = Blocks {top :: [Int]
				, bottom  :: [Int]
				, left :: [Int]
				, right :: [Int]}
				deriving (Show)

data Machine = MOK BlockDispersion [Action] | MError BlockDispersion [Action] deriving (show)


rSplitAt i xs = let (a, b) = splitAt i $ reverse xs in
	(reverse b, reverse a)
	
moveR :: Int -> ([a], [a]) -> ([a], [a])
moveR i (a, b) = let (c, d) = rSplitAt i a
			in (c, d++b)
moveL :: Int -> ([a], [a]) -> ([a], [a])
moveL i (a, b) = let (c, d) = splitAt i b
			in (a++c, d)
}}}


I am not sure what additional info to provide...
Running an Arch linux system, 8GB ram, installed ghc packgage should be as vanilla as can be...

{{{
[leo@derse brutelift]$ uname -a
Linux derse 3.3.1-1-ARCH #1 SMP PREEMPT Tue Apr 3 06:46:17 UTC 2012 x86_64 Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz GenuineIntel GNU/Linux
}}}

",bug,closed,normal,7.6.1,Compiler (Type checker),7.4.1,duplicate,"panic, impossible, type checker, renamer",,Linux,x86_64 (amd64),Compile-time crash,Unknown,,,,#5961