[r6rs-discuss] Re: [Formal] formal comment (ports, characters, strings, Unicode)

From: William D Clinger <will>
Date: Tue Mar 20 13:47:40 2007

I am posting this as an individual member of the Scheme
community. I am not speaking for the R6RS editors, and
this message should not be confused with the editors'
eventual formal response.

Thomas Lord wrote:
> I'd given some thought to that. You could describe it by saying
> that CHAR->INTEGER *must* be total over CHAR and *may* be
> a many-to-one function while INTEGER->CHAR *must* be
> non-divergent only for numeric scalar values and, over that
> domain, *must* be an injection into CHAR.

I did not describe what you just described. I described
an alternative in which "an implementation could add bucky
bits to characters while making those bits invisible to
all of the standard operations on characters and strings."
What you are describing would make those bits visible to
the standard operations.

> The language
> of 5.92 seems to me to explicitly forbid this interpretation but
> you have brought into consideration so let's see where it goes.

I did not propose anything that would violate the language
of the 5.92 draft.

> It is an interesting idea except that, in general, it needlessly
> leaves you with no coherent account of the standard CHAR
> ordering predicates and their induced ordering of STRINGS
> regarded as simple sequences of CHAR. It would leave
> Scheme with no generic sequence-of-char type or any way to
> write portable libraries for such a type.

That's true of your misinterpretation of my proposal, but is
not true of my proposal.

> Finally, I think there is a debate implicit in this explicit debate.
> It seems to me that you and Cowan would like Scheme programs
> to be type-safe in an unprecedented way that goes beyond the
> type safety goals of the report:

I appreciate the joke.

Will
Received on Tue Mar 20 2007 - 13:47:32 UTC