Re: [Scheme-reports] Comments on draft 6

[Jussi Piitulainen <jpiitula@x>]

Andy Wingo writes:

> On Fri 24 Feb 2012 13:53, Jussi Piitulainen writes:
> 
> > Implementations can do anything they like when the report says "it
> > is an error".
> 
> Implementations can do whatever they like, in general ;-)

But implementations _of R7RS_ can do what they like when R7RS says
that something "is an error". That statement does not require them to
_signal_ an error, or to do something silly.

I think that was John Cowan's point: to leave things unspecified in a
way that allows implementations to specify them if they like. (I'm
uneasy about assignments to variables that haven't been defined in the
program, so I don't care myself.)

> But consider:
> 
>   (define t 1)
>   (let ()
>     (define-syntax define-const
>       (syntax-rules ()
>         ((_ var val)
>          (begin
>            (define t val)
>            (define (var) t)))))
>     (define-const foo 2)
>     t)
> 
> In Scheme, this must evaluate to 1.  I think all implementations
> support this.
> 
> Now consider:
> 
>   (define t 1)
>   (define-syntax define-const
>     (syntax-rules ()
>       ((_ var val)
>        (begin
>          (define t val)
>          (define (var) t)))))
>   (define-const foo 2)
>   t
> 
> Does Scheme consider it a goal to specify the result of this
> program?

I don't know. Is it different from the following?

(define t 1)
(define t 2)
(define (foo) t)
t

(Yes, I may be missing a lot here. :)


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