Re: ratio implementation

[Marius Vollmer]

Bill Schottstaedt <address@hidden> writes:

> There is an implementation of ratios for Guile (based on CVS version
> of 27-Jul-03) at ccrma-ftp.stanford.edu:/pub/Lisp/gratio.tar.gz.
> Rather than send a huge diff, I placed the new versions of the changed
> files (all from the libguile directory) in the tarball along with
> *.diff showing the changes.

Good work, thanks!  However, I don't think we should restrict us to
longs as the numerator/denominator, we should use fixnums and bignums.
Your patch is a very good basis for this and it should be quite
straightforward to make it use SCM integers as the
numerator/denominator.

That is, instead of using "long", I'd say we simply use "SCM" and
instead of "+", "==", etc, we use use "scm_sum", "scm_num_eq_p", etc.
Also, instead of mallocing scm_t_ratio, we can use double cells, which
should be more efficient.

Any takers?

(Also I didn't really check whether your rationals behave like R5RS
demands it.  Did you?  We should be sure to follow R5RS.)

> I added numerator, denominator, rationalize and ratio?, and at the C
> level scm_make_ratio and scm_i_ratio2real (should it be
> scm_ratio2dbl?).  "ratio?" is needed because "rational?" returns #t
> if passed a real -- there has to be some way to distiguish a ratio
> from a real.

A ratio is exact, while a real is not.  Thus, I'd say that ratio? is
not really necessary.  There should be no reason to add anything eyond
R5RS for ratios.

> An alternative would be to make "rational?"  rational.

That would violate R5RS, wouldn't it?

> I don't know how the FSF/GPL copyright stuff works, but I did this
> work on my own time, did not look at any other implementation, and
> hereby donate the code to you.  I'd be happy to "sign the papers".

Thanks!  I'll get back to you about the papers when necessary.

> I decided to make minimal changes, but handling of exact/inexact
> distinctions in Guile could use some work (I am willing do this, if
> others approve).

That would be great!

> And currently (format #f "~F" 2/3) hangs, but so does (format #f
> "~B" 1.5) (in Guile 1.6.4 you get an error, but in the CVS Guile it
> hangs in mutex_lock).

This should be fixed in CVS.

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