Re: set! problem

["Robert D. Skeels" <athene at earthlink dot net>]

06/30/2000 07:37, Daniele Maraschi maraschi@lirmm.fr:

> I found something not very conformed to Standard Scheme:
> 
> [daniele@einstein kawa]$ java kawa.repl
> #|kawa:1|# (set! a 5)
> #|kawa:2|# a
> 5
> #|kawa:3|# 
> 
> I think probably I should get an error if I modified a variable
> that I haven't define before!!
> What do you think ?

Not being an expert, I can't say my response is qualified. However, after
reviewing sections 4.1.6 and 5.2.1 of the R5RS I find that you're correct.

From 5.2.1:
> ... whereas it would be an error to perform a `set!' on an unbound
> variable.

That being said, I find in practice it is implementation dependent on how
set! deals with unbound values. Some seem to treat set! in the same way as
define when a variable is unbound (see 5.2.1). GambitC treats set! on
unbound variables like Kawa does. SCM does not, and I haven't had time to
check any others.


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