On Tue, 2005-03-29 at 11:38, Juerd wrote:
> Luke Palmer skribis 2005-03-29 6:14 (-0700):
> > method iterate () {
> > for (@.objs) {
> > .process($_); # oops
> > }
> > }
[...]
> $_ is the topic, and I think that if we have two topics, Perl gets as
> convoluted as Japanese for someone who doesn't understand the language.
I've put a lot of thought into this one since topics were first
broached. It's been nagging at me, and I think I see a solution.
Use "given" as a statement (not a block control operator):
given :invocant;
This binds $_ to the current invocant.
given 1;
given maintains a stack (which, itself is lexically scoped, so you don't
get to reach into a caller's givens), so here we request the 1th
(zero-indexed, of course) context.
If we call given's stack @_given, then the above statement is just:
$_ := @_given[1];
Any implicit binding of $_ other than through the use of "given" inserts
the new value into the stack, so you can do:
given 1;
given 0;
given 1;
Without changing the given stack (important for maintainable code).
This is distinct from:
given 1 { ... }
In which we bind $_ to the number 1.
This also works with labels:
OUT: for @a {
IN: for @b {
given OUT; say "Outer scope {$_}";
given IN; say "Inner scope {$_}";
}
}
by determining the @_given entry that was active in the given scope (ok,
so @_given actually contains more information than just the value
itself).
It would be potentially interesting to introduce a "give" keyword for
this purpose:
map {map {give 1} 0..1000} @foo;
which simply returns the value of {given 1;$_}
--
Aaron Sherman <[EMAIL PROTECTED]>
Senior Systems Engineer and Toolsmith
"It's the sound of a satellite saying, 'get me down!'" -Shriekback
