Michael G Schwern writes:
: Reading this in Apoc 4
:
: sub mywhile ($keyword, &condition, &block) {
: my $l = $keyword.label;
: while (&condition()) {
: &block();
: CATCH {
: my $t = $!.tag;
: when X::Control::next { die if $t && $t ne $l); next }
: when X::Control::last { die if $t && $t ne $l); last }
: when X::Control::redo { die if $t && $t ne $l); redo }
: }
: }
: }
:
: Implies to me:
:
: A &foo prototype means you can have a bare block anywhere in the
: arg list (unlike the perl5 syntax).
That is correct.
: Calling &foo() does *not* effect the callstack, otherwise the
: above would not properly emulate a while loop.
Maybe it's transparent to caller but not to caller($n). I'm not sure how
much of a problem this will be. Inside &block it's a closure, which
carries a lot of the context you need already. Continuations may be
overkill.
: If that's true, can pull off my custom iterators?
: http:[EMAIL PROTECTED]/msg08343.html
:
: Will this:
:
: class File;
: sub foreach ($file, &block) {
: # yeah, I know. The RFC was all about exceptions and I'm
: # not using them in this example.
: open(FILE, $file) || die $!;
That's
my $FILE = open $file || die;
and so on.
: while(<FILE>) {
: &block();
: }
:
: close FILE;
: }
:
: allow this:
:
: File.foreach('/usr/dict/words') { print }
File.foreach('/usr/dict/words', { print })
or even (presuming the prototype is available for parsing):
File.foreach '/usr/dict/words' { print }
: or would the prototype be (&file, &block)?
:
: And would this:
:
: my $caller = caller;
: File.foreach('/usr/dict/words') {
: print $caller eq caller ? "ok" : "not ok"
: }
:
: be ok or not ok? It has to be ok if mywhile is going to emulate a
: while loop.
I don't see why the default caller has to be caller(1). In any event,
user-define control code will need to be able to get out of the way
of the programmer's expectations. A return certainly needs to return
from the surrounding lexical sub block, not from a mere bare block.
Larry
