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Re: overriding car/cdr

From: Paul Jarc
Subject: Re: overriding car/cdr
Date: Sun, 08 Feb 2004 15:56:09 -0500
User-agent: Gnus/5.110002 (No Gnus v0.2) Emacs/21.3 (gnu/linux)

Marius Vollmer <address@hidden> wrote:
> But car/cdr are not a good way to work with general sequences.  Think
> of vectors.

car/cdr certainly can be made to work with vectors.  Making them work
with arbitrary user-defined structures would give us a lot of
flexibility without too much work.

If there is a significant amount of C code using SCM_CAR/SCM_CDR with
non-pair objects, then it might be best to leave them unchanged.  But
I think the Scheme-level cxr functions would be a good place to make
the change.

> We should not try hard to turn car/cdr into something abstract
> (which they are not, even their names come from the lowest level).

Of course they currently are not, but that doesn't (nor do the names)
tell us whether it would be good if they were more abstract.

> Somehthing like the 'sequence' concept of Common Lisp is a better
> approach, I'd say.

AFAICT, that would involve a whole new set of procedures to work with
this new data type.  I'm suggesting modifying the existing procedures
so that most existing code would automatically be able to take
advantage of the new flexibility, with no further changes needed.


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