yes it can reuse an upper and precedent definition but a nested definition
can not be used later at an upper level.
anyway it would not be portable , for all those reason i will use to
separate operator ,basically <- for set! and <+ for define ,so i can even
modify toplevel bindings , i did not want to have all the python behavior
which is not safe and did not allow local nested variables.
even using an exception will not solve the problem:
scheme@(guile-user)> (call-with-current-continuation
(lambda (exit)
(with-exception-handler
(lambda (e)
(exit "undefined ,you need to define somewhere")) (lambda () (set!
notdefined 7)))))
;;; <stdin>:97:69: warning: possibly unbound variable `notdefined'
$28 = "undefined ,you need to define somewhere"
??? i do not see any solution with a macro with exception
Damien
On Thu, Sep 23, 2021 at 10:27 PM Taylan Kammer <[email protected]>
wrote:
> On 23.09.2021 19:27, Damien Mattei wrote:
> > yes i know parsing the whole code is the only portable solution, but it
> is slow,even on a few dozen of lines the slowing is visible ,so i can even
> think of that on one thousand lines...
> >
> > I finally succeed in Guile with simple piece of code to make my example
> run with a single assignment operator <- , here i define for variable the
> assignment operator <$ , <- is working with arrays too:
> >
> > *Preview:*
> >
> > (define-syntax <$
> >
> > (lambda (s)
> >
> > (syntax-case s ()
> >
> > ((_ var value)
> >
> > (case (syntax-local-binding #'var)
> >
> > ((lexical) #'(begin
> > (display "<$ : lexical scope : ")
> > (display (quote var))
> > (newline)
> > (set! var value)))
> >
> > ((displaced-lexical) #'(begin
> > (display "<$ : displaced-lexical scope :
> ")
> > (display (quote var))
> > (newline)
> > (set! var value)))
> >
> > ((global) #'(begin
> > (display "<$ : global scope : ")
> > (display (quote var))
> > (newline)
> > (define var value)))
> >
> > (else #'(begin
> > (display "<$ : unknow variable scope :")
> > (display (quote var))
> > (error "<$ : unknow variable scope : "))))))))
> >
>
> I can't seem to find syntax-local-binding in Guile 2.2 or 3.0. Did you
> have to import some special module, or are you using another version?
>
> Either way, I suspect that the following will not work with your macro:
>
> (let ()
> (let ()
> (<$ x 1))
> (display x)
> (newline))
>
> If I understand correctly, it will expand to:
>
> (let ()
> (let ()
> (define x 1))
> (display x)
> (newline))
>
> And that won't work because 'x' is only defined in the inner 'let'.
>
> This is where we see the crucial difference between Scheme and Python:
> in Python there is nothing similar to an inner 'let'. There is only
> one function-level scope. In Scheme, there can be as many nested
> scopes as you want, and an inner scope can't affect an outer one.
>
> --
> Taylan
>
