[Hugs-users] Network.CGI missing in Hugs

Bjorn Bringert bringert at cs.chalmers.se
Wed Jan 10 07:32:56 EST 2007

On Jan 9, 2007, at 22:35 , Claus Reinke wrote:

>> - The existing module used undecidable instances, a Haskell  
>> extension  which is supported by GHC but not by Hugs.
> ??
> as far as i recall, Hugs was the first Haskell implementation to  
> bite the
> bullet and accept undecidable instances as a design option  
> (although its
> predecessor apparently also had the undecidability feature).
> http://cvs.haskell.org/Hugs/pages/users_guide/class-extensions.html
> are you thinking of interactions with other extensions, perhaps?

Sorry, my bad, that was confused. Some earlier comments from this  
thread to add to the confusion:

Sven Panne wrote:
> Effectively removing Network.CGI from the Hugs community will  
> probably break
> more programs, so I'll vote for non-overlapping instances, too.

Ian Lynagh wrote:
> Hugs compatibility is also important, though, and undecidable  
> instances
> are marked "probably no" for Haskell'.

The bottom line is that the instance:

instance (MonadTrans t, MonadCGI m, Monad (t m)) => MonadCGI (t m) where

needs both overlapping and undecidable instances, doesn't work in  
Hugs, and probably won't be Haskell'-compatible. However, the problem  
should be solved now, since that instance is no longer in the cgi  


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