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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

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	GhciCrash
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture