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Postings from December 2002
On Tue, Dec 24, 2002 at 01:20:06PM +1100, Martien Verbruggen wrote:
> If the block did the localisation, then the line starting with 4: would
> read the same as the line starting with 2:, since $1 gets set in the
> conditional of the while() loop, not inside the block. To see what I
> mean, try this:
> or even this:
>
> $ perl -wl
> $_ = "ab";
> /(.)$/;
> print "1: $1";
> for (/(.+)/g)
> {
> print "2: $1";
> /(.)/;
> print "3: $1";
> }
> print "4: $1";
> __END__
> 1: b
> 2: ab
> 3: a
> 4: ab
>
> In neither of these two cases the localisation occurs. It only occurs
> when the while() is used.
> But I merely wanted to draw attention to the discrepancy in
> documentation and behaviour. I don't _know_ what is correct and what
> isn't, since that is the domain of the p5p to discuss.
There does seem to be something astray, as these two aren't equivalent:
$ perl -wl
$_ = "ab";
/(.)$/;
print "1: $1";
while (/(.+)/g) {
}
print "4: $1";
__END__
1: b
4: b
$ perl -wl
$_ = "ab";
/(.)$/;
print "1: $1";
1 while (/(.+)/g);
print "4: $1";
__END__
1: b
4: ab
They don't seem to compile to the same ops - the former's loop is:
COP (0x16d828) nextstate
BINOP (0x16d800) leaveloop
LOOP (0x16d7d0) enterloop
UNOP (0x16d7b0) null
LOGOP (0x16d788) and
PMOP (0x16d4e8) match /(.+)/
LISTOP (0x16d760) lineseq
COP (0x16d6c0) nextstate
OP (0x16d700) unstack
COP (0x16d720) nextstate
the latter is:
COP (0x16d7b8) nextstate
LISTOP (0x16d790) leave
OP (0x16d770) enter
UNOP (0x16d750) null
LOGOP (0x16d728) and
PMOP (0x16d508) match /(.+)/
LISTOP (0x16d700) lineseq
OP (0x16d4d8) null [5]
OP (0x16d6e0) unstack
I don't know what the significance of all this is. The for loop compiles
to a third set of ops. I get the impression that the while loop's condition
is scoped within the block, whatever the documentation may say.
Nicholas Clark
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