[Haskell-cafe] advanced class constraints in Haskell 98?

Ross Paterson ross at soi.city.ac.uk
Thu Jan 8 19:25:27 EST 2009

On Fri, Jan 09, 2009 at 01:11:12AM +0100, Henning Thielemann wrote:
> Maybe the report is not complete? I mean, the current behaviour of Hugs  
> and GHC (as I observed it) is more consistent, and maybe that's what the  
> designers had in mind.

I'm puzzled by the Hugs behaviour.  The current version rejects it, and
I downloaded and built the Mar2005 version just to check, and it also
rejected it, saying

	Illegal Haskell 98 class constraint in class declaration

I think the GHC behaviour is connected with GHC's deferred context
reduction, which also does not conform to Haskell 98.

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