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

[Henning Thielemann]

On Fri, 9 Jan 2009, Miguel Mitrofanov wrote:

> On 9 Jan 2009, at 02:47, Ross Paterson wrote:
>
>> On Thu, Jan 08, 2009 at 10:27:59PM +0100, Henning Thielemann wrote:
>>> A nice. I jumped into 4.3 and found
>>> 
>>> scontext -> simpleclass
>>>        | (simpleclass_1, ..., simpleclass_n)
>>> 
>>> simpleclass -> qtycls tyvar
>>> 
>>> So it must be 'atype' instead of 'tyvar'? Haskell 98 is really mighty.
>> 
>> Oh.  Don't I look silly?  You were absolutely right, it's not Haskell 98.
>
> Me too. I've looked at the type declaration syntax instead of instance 
> declaration one.

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.

>> Actually Hugs does reject it without flags.  Maybe you have a -98 stored
>> somewhere?

When starting, my Hugs tells

Haskell 98 mode: Restart with command line option -98 to enable extensions