id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
1176,Infinite loop when printing error message,Paul_Berry@…,thorkilnaur,"I am trying to compile a file that has a known compile error.  Ghc gets into an infinite loop trying to output the error message.

Here's the session (captured using EMACS shell):

{{{
pberry@Dal:~/bridge_ghc_bug$ uname -a
Linux Dal 2.6.18-3-686 #1 SMP Mon Dec 4 16:41:14 UTC 2006 i686 GNU/Linux
pberry@Dal:~/bridge_ghc_bug$ gcc -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr --with-tune=i686 --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
pberry@Dal:~/bridge_ghc_bug$ ghc -v --make main.hs
Glasgow Haskell Compiler, Version 6.6, for Haskell 98, compiled by GHC version 6.6
Using package config file: /usr/lib/ghc-6.6/package.conf
wired-in package base mapped to base-2.0
wired-in package rts mapped to rts-1.0
wired-in package haskell98 mapped to haskell98-1.0
wired-in package template-haskell mapped to template-haskell-2.0
Hsc static flags: -static
*** Chasing dependencies:
Chasing modules from: main.hs
Stable obj: []
Stable BCO: []
compile: input file main.hs
Created temporary directory: /tmp/ghc5182_0
*** Checking old interface for main:Main:
[1 of 1] Compiling Main             ( main.hs, main.o )
*** Parser:
*** Renamer/typechecker:

main.hs:30:12:
    No instance for (Show Rank)
      arising from use of `show' at main.hs:30:12-19
    Possible fix: add an instance declaration for (Show Rank)
    In the first argument of `(~?=)', namely `show Ten'
    In the expression: (show Ten) ~?= ""T""
    In the second argument of `($)', namely
	`[(show Two) ~?= ""2"", (show Three) ~?= ""3"", (show Four) ~?= ""4"",
      (show Five) ~?= ""5"", (show Six) ~?= ""6"", (show Seven) ~?= ""7"",
  (show Eight) ~?= ""8"", (show Nine) ~?= ""9"", (show Ten) ~?= ""T"",
}}}

At this point ghc goes into an (apparently) infinite loop outputting spaces.  When I interrupt it using Ctrl-C, it says:

{{{
*** Deleting temp files:
Deleting: /tmp/ghc5182_0/ghc5182_0.s
Warning: deleting non-existent /tmp/ghc5182_0/ghc5182_0.s
*** Deleting temp dirs:
Deleting: /tmp/ghc5182_0
}}}

Here's the file main.hs:

{{{
import System
import Test.HUnit
import Control.Monad
import Data.List

data Card = Card Rank Suit

data Suit = Clubs | Diamonds | Hearts | Spades
    deriving (Enum, Eq)

data Rank = Two | Three | Four | Five | Six | Seven | Eight | Nine | Ten | Jack | Queen | King | Ace
    deriving (Enum, Ord, Eq)

type Hand = [Card]

hand :: String -> Hand
hand = undefined

main = undefined

allTests = test $
           [show Two ~?= ""2""
           ,show Three ~?= ""3""
           ,show Four ~?= ""4""
           ,show Five ~?= ""5""
           ,show Six ~?= ""6""
           ,show Seven ~?= ""7""
           ,show Eight ~?= ""8""
           ,show Nine ~?= ""9""
           ,show Ten ~?= ""T""
           ,hand ""AK76543/32/AK2/3"" ~?= exampleHand
           ]
    where exampleHand = []
}}}",bug,new,low,_|_,Compiler,6.6,,,dterei,Unknown/Multiple,Unknown/Multiple,None/Unknown,Unknown,tcfail177,,,