At 06:48 PM 8/20/00 -0600, Tony Olekshy wrote:
>Dave Rolsky wrote:
> >
> > Tony Olekshy wrote:
> >
> > > try { fragile(); }
> > > catch { my $caught = 1; }
> > > finally { $caught and ... }
> >
> > If all those pieces were in the same scope I think it would still
> > work like this (in Perl5-ish code):
> >
> > {
> > try { fragile(); # It must be Italian }
> > my $caught;
> > catch { $caught = 1; }
> > finally { $caught and ... }
> > }
> >
> > It's the same as in perl5 with a block:
> >
> > {
> > print $foo;
> > my $foo = 1;
> > }
> >
> > This is a compile time error because $foo isn't in scope til its
> > declared.
>
>But in the shared scope, $catch isn't referenced until after the my
>in lexical order. I'm just worrying about the details of what happens
>during the dynamics of execution. I think it's more like saying:
>
> {
> if ($foo) { my $bar = 1; }
> $bar and ...
> }
>
>where the outer block represents this "shared lexical scope" concept.
>For this to work, doesn't storage for $bar have to be allocated and
>initialized to undef at the beginning of the outer block?
Nope. It should work as though each pair of } ... { in between try { and
the end of the last finally or catch block isn't there. Storage for
lexicals is allocated at compile time, assignment happens at run time. You
can coerce some odd-looking behavior out of perl if you exploit this.
However, my memory as to what the current perl behavior is was faulty;
continue blocks do *not* share the lexical scope of their attached loop
blocks. I was misremembering the caveat at the end of this part of perlsyn
(which says the opposite, and is easily confirmed):
>Perl's C-style for loop works exactly like the corresponding while loop; that
>means that this:
>
> for ($i = 1; $i < 10; $i++) {
> ...
> }
>
>is the same as this:
>
> $i = 1;
> while ($i < 10) {
> ...
> } continue {
> $i++;
> }
>
>(There is one minor difference: The first form implies a lexical scope for
>variables
>declared with my in the initialization expression.)
So no, what I'm proposing is not the same as anything currently in
Perl. But I think it's a good reason anyway (and why shouldn't continue
blocks share the same scope? Not so 'lexical', I suppose. Oh well.)
--
Peter Scott
Pacific Systems Design Technologies
