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Re: hash-table-*/default (Re: SRFI 69 update)

This page is part of the web mail archives of SRFI 69 from before July 7th, 2015. The new archives for SRFI 69 contain all messages, not just those from before July 7th, 2015.

On Wed, Aug 31, 2005 at 08:30:12PM +0100, Tony Garnock-Jones wrote:
> > True, but the implementation is already there for those who want
> > something rigorous. :)
> So long as the implementation is *normative* and not simply
> *informative*, then fine. That needs to be made clear, though.

No, the problem is exactly that the implementation is half-normative,
half-informative.  If I specify the behaviour of e.g.
hash-table-ref/default by writing code, I must also specify just how
normative the implementation is.  For example, if I said:


	Behaves as if defined by
	(define (hash-table-ref/default ht key default)
	  (hash-table-ref ht key (lambda () default)))

Then, is this a valid implementation anymore:

(define (hash-table-ref/default ht key default)
  (set! *log* (cons "hash-table-ref/default called" *log*))
  (hash-table-ref ht key (lambda () default)))

?  I would say it is not, because it does not behave anymore as if it
was defined as in the spec.  (value-)equivalence of expressions is
better because it makes contracts about the return value of a function

I think I'm going for the "evaluates to" version, unless further
discussion emerges.

> > It's just that viewed differently, (hash-table-ref) can be seen as a
> > kind of control structure, similar to (and) or (if).
> Careful! The logical endpoint of this kind of thought is normal-order
> evaluation... :)



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