From: Mark Raynsford <list+org.sourceware.kawa@io7m.com>
To: Per Bothner <per@bothner.com>
Cc: kawa@sourceware.org
Subject: Re: Difference in define behaviour between kawa.jar and embedded Scheme example
Date: Thu, 23 Nov 2017 10:52:00 -0000 [thread overview]
Message-ID: <20171123105212.0e8cbd1d@copperhead.int.arc7.info> (raw)
In-Reply-To: <e9ec95ea-9e61-5576-3a0d-a45c1c1cdb18@bothner.com>
[-- Attachment #1: Type: text/plain, Size: 2034 bytes --]
Hello!
On 2017-11-23T03:26:20 +0100
Per Bothner <per@bothner.com> wrote:
>
> On 11/22/2017 11:33 PM, Mark Raynsford wrote:
> > In other words, the redefinition of + on the second line is affecting
> > the existing definition of six0 so that the applications of six0 and
> > six1 are both returning 9. What's going on here?
>
> The behavior of demo0.scm depends on whether it is evaluated line-by-line
> (as in REPL) or as a "module" (or "library" in R7RS-speak). The latter
> is the default, but you can force teh former using the -f options.
> Compare:
> $ kawa demo0.scm
> vs:
> $ kawa -d demo0.scm
>
> Either implicitly imports (kawa base). In general it is invalid to
> explicitly define bindings that conflict with imported bindings.
> We are somewhat more lenient with (kawa base), for compatibility
> with tradition, but it is still a bad idea.
OK, thanks. This is something I'm going to be looking into at the
source. As you know, I'm putting together a gratuitously incompatible
subset of the language, so I have no need for compatibility with
tradition. I'd rather get hard errors up front. To be honest, I'd
rather all redefines at the top-level be errors, but I assume this is
something I'm going to have to implement myself.
I actually ran into this behaviour because I was informally testing my
subclasses of Scheme/SchemeCompilation and was surprised that I could
override existing bindings like this (because being able to affect the
internals of existing definitions wasn't the behaviour I was used to
from other Schemes). I assumed that I'd broken something with my
subclasses, but then it turned out that the original Scheme class also
did this.
> Instead you can do something like:
>
> (import (except (kawa base) +))
> (import (only (kawa base) (+ orig-+)))
> (define (six0 x) (orig-+ 3 3))
> (define (+ x y) (* x y))
> (define (six1 x) (+ 3 3))
> (format #t "[~w ~w]~%~!" (six0 0) (six1 0))
Got it.
--
Mark Raynsford | http://www.io7m.com
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2017-11-23 10:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-22 22:33 Mark Raynsford
2017-11-23 2:26 ` Per Bothner
2017-11-23 10:52 ` Mark Raynsford [this message]
2017-11-23 12:51 ` Per Bothner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20171123105212.0e8cbd1d@copperhead.int.arc7.info \
--to=list+org.sourceware.kawa@io7m.com \
--cc=kawa@sourceware.org \
--cc=per@bothner.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).