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From: Mark Raynsford <>
To: Per Bothner <>
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: <> (raw)
In-Reply-To: <>

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On 2017-11-23T03:26:20 +0100
Per Bothner <> 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 |

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  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

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