Class System current status

Bulat Ziganshin bulat.ziganshin at
Fri May 12 07:30:01 EDT 2006

Hello Stephanie,

Thursday, May 11, 2006, 5:45:15 PM, you wrote:

>   - We're already in that state. There *is* a lot of Haskell code that
> uses FDs, it's just not Haskell 98 code. Whenever ATs take over, we'll
> still have to deal with this code.

are you sure about *lots* ?  i seen only 3-4 ones (monad transformers,
collections, may be arrays, my streams) and think that all these
libraries can be redesigned without any problems once in several
years. that is really important is that CLIENTS of these libraries
don't need to be changed

>   - It may be that all uses of MPTCs/FDs may be subsumed by ATs, and in
> fact there is (or will be) some automatic way of translating FD code to
> AT code.

i think that is not necessary considering that i said above

>   - It may not be all bad for a future Haskell standard to include both
> ATs and FDs. Certainly more complicated, but I haven't seen any evidence
> that these features interfere with eachother.

language should be orthogonal, i.e. include only one way to implement
each feature. otherwise, it becomes too large

> Are there any merits to these counterarguments?

> More generally, our discussion about the class system seems to be 
> stalled. How should we to come to a decision?

i think the same - goal of discussion should be developing of
proposal/proposals in this area for Haskell' committee. any other
directions of discussion, while very important for future of Haskell
language, should be somewhat limited or moved to cafe list.

i propose the following structure of discussions:

1. initial proposal
2. critique
3. correction of proposal and going to 2nd step
4. final proposal or abandoning this proposal

making several concurrent proposals on the same topic would be great
because concurrency motivates to make better things and because ideas
can be easily borrowed by proposals from each other

Best regards,
 Bulat                            mailto:Bulat.Ziganshin at

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