Local variables not so local within block

Thank you for this new version of blex and for the further explanation
about the behaviour of "local".
Well, I'm interested in trying the new lexical scope in Maxima... I've
rapidly tested the implementation of blex, and although it is simple, as
you said, it seems to work fine. I could even replace all the block
instances with blex in my program to see if it works. Just to make some
further tests... Anyway, I hope to see lexical scope implemented in Maxima
in the near future!

Stefano



2012/7/24 Robert Dodier <robert.dodier at gmail.com>

> On 2012-07-23, Stefano Ferri <ferriste at gmail.com> wrote:
>
> > I've tried your implementation of "blex". It seems to work fine, do you
> > think it could be used in a (more or less) stable code?
>
> Well, blex is pretty simple-minded, so, although you can't expect much,
> you can expect it to do its simple thing ....
>
> > Anyway it doesn't support the "return" statement, Maxima complains
> > that return is not inside a block.
>
> Oh, you're right. I've appended an updated blex.lisp to this message.
>
> > But, reading the documentation of block, I've just discovered the
> > "local" command, wich seems to solve the problem.
>
> Well, the effect of local is to remove properties from a symbol, so
> there is a different set of unexpected consequences that are possible:
>
> foo[123] : 456;
> g(x) := foo[x];
> g(123);
>  => 456
> f(x) := block (local(foo), foo:something, g(x));
> f(123);
>  => foo[123]
>
> best,
>
> Robert Dodier
>
> PS.
>
> ;; blex.lisp -- lexical block for Maxima
> ;; copyright 2012 by Robert Dodier
> ;; I release this work under terms of the GNU GPL
> ;;
> ;; examples:
> ;; blex ([n:100], f(x) := n : n + x, g() := display(n));
> ;; blex ([f], f(x) := 2*x);
> ;; blex ([a], h(x) := a[x] : 1, i() := arrayinfo(a));
>
> (defmspec $blex (x)
>  (let*
>    ((args (cdr x))
>     (vars+inits (cdr (car args)))
>     (vars (mapcar #'(lambda (e) (if (symbolp e) e (second e))) vars+inits))
>     (inits (remove-if #'symbolp vars+inits))
>     (exprs (cdr args))
>     (gensym-vars (mapcar #'(lambda (s) (let ((s1 (gensym))) (setf (get s1
> 'reversealias) (or (get s 'reversealias) s)) s1)) vars))
>     (subst-eqns (mapcar #'(lambda (x y) `((mequal) ,x ,y)) vars
> gensym-vars))
>     (gensym-mprog ($psubstitute `((mlist) , at subst-eqns) `((mprog)
> ((mprogn) , at inits) , at exprs))))
>    (meval gensym-mprog)))
>
>
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