Bug#334337: hugs segfault if Show class in instancied but show method not defined.

2005-10-17 Thread Bill Allombert 
Package: hugs
Version: 98.200503.08-3
Severity: normal

Hello Isaac,

It looks like hugs segfault if you instancy Show but not define a
show method and then implicitly use it:

Let foo.hs =
--->8-
module Fibo where
type Quad = (Integer,Integer)
newtype Gauss = Karl Quad
instance Eq Gauss where
   Karl (a,b) == Karl (c,d) = a == c && b == d
instance Show Gauss where
---8<-
in 
$ hugs fibo3.hs
Type :? for help
Fibo> Karl (1,2)
zsh: segmentation fault  hugs fibo3.hs

Cheers,
-- 
Bill. <[EMAIL PROTECTED]>

Imagine a large red swirl here. 

-- System Information:
Debian Release: testing/unstable
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.4.27
Locale: LANG=fr_FR, LC_CTYPE=fr_FR (charmap=ISO-8859-1)

Versions of packages hugs depends on:
ii  libc6 2.3.5-6GNU C Library: Shared libraries an
ii  libncurses5   5.4-9  Shared libraries for terminal hand
ii  libreadline5  5.0-11 GNU readline and history libraries


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Bug#334337: hugs segfault if Show class in instancied but show method not defined.

2005-10-17 Thread Ross Paterson 
On Mon, Oct 17, 2005 at 11:52:56AM +0200, Bill Allombert wrote:
> It looks like hugs segfault if you instance Show but not define a
> show method and then implicitly use it:
> 
> Let foo.hs =
> --->8-
> module Fibo where
> type Quad = (Integer,Integer)
> newtype Gauss = Karl Quad
> instance Eq Gauss where
>Karl (a,b) == Karl (c,d) = a == c && b == d
> instance Show Gauss where
> ---8<-
> in 
> $ hugs fibo3.hs
> Type :? for help
> Fibo> Karl (1,2)
> zsh: segmentation fault  hugs fibo3.hs

This is an instance of Hugs segfaulting on some infinite computations
(here show -> showsPrec -> show).  You can do the same thing with an
empty Eq instance or just

let f x = g x + 1; g x = f x + 2 in f 3

The general problem is documented in the User's Guide, but I believe
it's fixed in CVS version (src/machine.c 1.25 and src/prelude.h 1.79
if anyone's interested in backporting).



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