Re: [Caml-list] Clarification for the configuration of comparison functions

[Yotam Barnoy <yotambarnoy@gmail.com>]

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Another reason is performance. The generic, polymorphic comparison function
drops you out into C (which has a cost) and has to compare every single
possible value combination. A customized comparison function stays in ocaml
and handles only what you need ie. it's driven by type information that the
generic function lacks.

Yotam

On Wed, Sep 10, 2014 at 7:27 AM, Gerd Stolpmann <info@gerd-stolpmann.de>
wrote:

> Am Mittwoch, den 10.09.2014, 10:56 +0200 schrieb SF Markus Elfring:
> > Hello,
> >
> > I extended my software development experience a bit for the programming
> language
> > "OCaml". I find my knowledge incomplete here to resolve an issue like
> > "Comparison function application" alone.
> > https://github.com/elfring/OTCL/issues/4
>
> There are three reasons why you want to have your own comparison
> function:
>
> - You need a different ordering than provided by Pervasives.compare.
>   For compound types the ordering of compare is implementation-defined,
>   and currently the implementation prefers the fastest way of comparing.
>   E.g. if you compare arrays, you don't get a lexicographic ordering.
>   This is sometimes not what you need.
> - Your values are cyclic. compare may hang if you try to compare cyclic
>   values.
> - Your values contains parts that cannot be compared, like functions.
>   With a custom comparison function you can skip these parts.
>
> Gerd
>
> > How do you think about to discuss corresponding implementation details
> for an
> > evolving class library?
> >
> > I would appreciate your advices.
> >
> > Regards,
> > Markus
> >
>
> --
> ------------------------------------------------------------
> Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
> My OCaml site:          http://www.camlcity.org
> Contact details:        http://www.camlcity.org/contact.html
> Company homepage:       http://www.gerd-stolpmann.de
> ------------------------------------------------------------
>
>

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