Class System current status

[Stephanie Weirich]

Simon Peyton-Jones wrote:
> My suggestion is this:
>
> * Specify MPTCs in the main language
>
> * Specify FDs in an Appendix (with some reasonably conservative
> 	interpretation of FDs). 
>
> * A Haskell' implementation should implement the Appendix, and
> 	programmers can write programs against it.  But
> 	we are advertising specifically that we aren't sure, one way
> 	or the other, whether FDs will stay in the language for ever
>
>   
Simon,

Why is an Appendix is better than just a footnote in the Standard that 
says "we aren't sure, one way or the other, whether FDs will stay in the 
language for ever."  Why do we need this extra structure?

I'm worried that this extra structure could be confusing. In particular, 
if someone says "this program is pure Haskell'"  what will that mean? In 
practice, will it be clear whether pure Haskell' includes the Appendix? 

--Stephanie