# Closures, compile time, pad protos

Hi,

Anatoly and I don't know what this bit of code prints:

foo();
foo();
for 1..3 {
my \$x ::= 3;
sub foo { say ++\$x };
say ++\$x
};

Is it 4, 5, 6, 6, 6 or 4, 5, 3, 3, 3? It's almost definitely not 4,
5, 6, 7, 8.

I can't rationalize 4, 5, 6, 7, 8 while maintaining the notion that
\$x is actually lexical.

To rationalize the other examples:

4, 5, 6, 6, 6 means that the foo declaration does not capture over
an instance of the \$x bar, but the actual value in the pad proto
itself (the value that will be the default value of newly allocated
\$x variabless).

4, 5, 3, 3, 3 means that at compile time all variables are
instantiated once for BEGIN time captures. Observe:

foo();
bar();
for 1..3 {
my \$x;
sub foo { say ++\$x }
sub bar { say ++\$x }
say ++\$x;
}

prints 1, 2, 1, 1, 1 because \$x is allocated once at  compile time
and captured into both foo and bar, and then separately allocated
once more for each iteration of the loop.

If this is indeed the case, then there is a semantics problem:

foo();
foo();
for 1..3 {
my \$x; BEGIN { \$x = 3 };
sub foo { say ++\$x };
say ++\$x
};

Must be 4, 5, 1, 1, 1. This is because BEGIN { } and the
foo share the same compile time allocated copy of \$x, but this is
not the copy in the loop.

A related issue is:

foo();
foo();
for 1..3 {
my \$x = 10;
sub foo { say ++\$x };
say ++\$x;
}

Is that 11, 12, 10, 10, 10, or 11, 12, 13, 13, 13, or 1, 2, 10, 10, 10?

Lastly,

sub foo {
my \$x;
sub { sub { say ++\$x } }
};

my \$bar = foo();

my \$gorch = \$bar.();

\$gorch.();
\$gorch.();

my \$quxx = \$bar.();

\$quxx.();
\$quxx.();

obviously results in the sequence 0, 1, but does the second call to
\$bar create a new sequence in \$quxx, or is that instance of \$x
shared between \$gorch and \$quxx? Intuitively i'd say it is shared,
which means that the outer sub declaration implicitly captures \$x as
well.  Can anyone confirm?

Obviously

my \$zot = foo().();
\$zot.();
\$zot.();

Does create a new sequence.

--
Yuval Kogman <[EMAIL PROTECTED]>
http://nothingmuch.woobling.org  0xEBD27418

pgplPyMaquTyx.pgp
Description: PGP signature