[R6RS] Enumerations proposal pre-draft

Michael Sperber sperber at informatik.uni-tuebingen.de
Thu May 18 13:14:15 EDT 2006

William D Clinger <will at ccs.neu.edu> writes:

> Sounds good to me.  I presume you are agreeing to eliminate the
> zero-argument overloading of <index-of> (which no longer performs
> an essential function anyway).  


> For <type-name>, how about we make it into a procedure of zero
> arguments that returns the universe as a set?

No.  I meant "giving in" in the sense of "accept your proposal, with
overloading", not doing something else.

> Are you referring to the limitations of the <type-name> macro we
> are agreeing to flush?

No.  (And we aren't :-) )

My previous proposal had a separate macro for creating enumeration-set
types, which could be used with the macro for creating enumeration
types, but also with other mechanisms for creating finite sets of
values, whatever they are.  (Such as Scheme 48's opaque enumerations,
or, more importantly, its finite types.)  So, if you want that, you
need an additional something just like the macro I proposed.  (But we
don't need it for R6RS, and it could be added later.)

> The real problems with extending the proposal to allow arbitrary
> elements in enumeration sets are that you'd have to specify the
> meaning of equality, and you'd have to worry about interactions
> between mutation and your Fundierung axiom(s).

I don't think so.  I think just specifying eqv? is enough.  But we
don't seem to be going there, anyway.

Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla

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