Re: [Gauche-devel] redefining "define" does not result in an error

[Shiro K. <sh...@la...>]

Strictly speaking, it's not a descrepancy; "error" in R5RS merely 
means "it's not a valid R5RS program".   What happens when an
implementation encounters an erroneous code is entirely up to
the implementation.  It can raise an exception, crash, handle
it gracefully, or handle it with additional semantics as an
extention of the language.

In this particular case, the problem is that if the syntactic
keyword is redefined in the middle of the program, there can
be different interpretations of the code.   Personally I think
an implementation should allow me to shoot myself if I wish,
so I might make this case issue a warning (just like redefining
a constant - which may break semantics of already-compiled code,
but you may want to do so sometimes, knowing the risk.)

--shiro


From: Dek...@Ya... (Benjamin L. Russell)
Subject: [Gauche-devel] redefining "define" does not result in an error
Date: Thu, 22 Jul 2010 07:48:18 +0900

> In Gauche 0.9, redefining "define" does not result in an error,
> contradicting Section 5.3 of the "Revised^5 Report on the Algorithmic
> Language Scheme" (see
> http://www.schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-8.html);
> _viz._:
> 
>         gosh> (define define 3)
>         define
>         gosh> define
>         3
>         gosh> (define first car)
>         *** ERROR: invalid application: (3 #0=#<subr car> #0#)
>         Stack Trace:
>         _______________________________________
>         gosh> 
> 
> Section 5.3 specifically states the following:
> 
>> ... it is an error for a definition or syntax definition to shadow a
>> syntactic keyword whose meaning is needed to determine whether some form
>> in the group of forms that contains the shadowing definition is in fact
>> a definition.... For example, the following are errors:
>> 
>> (define define 3)
> 
> Perhaps this discrepancy should be resolved.
> 
> -- Benjamin L. Russell
> -- 
> Benjamin L. Russell  /   DekuDekuplex at Yahoo dot com
> http://dekudekuplex.wordpress.com/
> Translator/Interpreter / Mobile:  +011 81 80-3603-6725
> "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^ 
> 
> 
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