Re^2: Yet Another Program on Closures ~ Steven Lembark ~ TPRC 2025 - YouTube

[hippo]

Other languages seem to use it other ways, including to mean any anonymous ... sub.

If an anonymous sub doesn't close over an external variable then it isn't a closure. The clue is in the name. :-)

[LanX]

> If an anonymous sub doesn't close over an external variable then it isn't a closure.

And if a named sub does, it's also a closure.

Indeed two unrelated concepts.

UPDATE

I just checked the etymology, the fact that the bound variables are not accessible from the outside of their defining scope makes the sub "closed".

{
    my $state = 42;

    sub closed_sub {
          return $state++;
    }
}

say closed_sub();  # 42
say closed_sub();  # 43

Contrary to subs binding global variables, which are "open".

{
    our $state = 42;

    sub open_sub {
          return $state++;
    }
}

say open_sub();    # 42
$main::state = 666;
say open_sub();  # 666

(of course Perl allows you to bind both kinds, so it's not an exclusive attribute here)

see references from WP:

<Reveal this spoiler or all in this thread>