# just as you can have a variable that contains strings and numbers,
# you can have a variable that contains subroutines.

my $subroutine = sub { print "Hello\n" };

# you can call this subroutine like so:

  $subroutine->();
  &$subroutine();

# you can also put a named subroutine into a variable

sub hello { print "Hi there!\n"; }
my $hello = \&hello;
&$hello();

# if you use a variable that is lexically bound to the scope
# the subroutine is defined in, you get what's called a closure

my @subs;
foreach my $adress ( "Sir", "Ma'am" )
{
    #each instance of the sub gets its own $adress 
    push @subs, sub { print "Good day $adress\n" }; 
}

$subs[0]->();
$subs[1]->();  

# if you call a subroutine that returns a subroutine, 
# you have what's called a factory

sub make_greeter {
  my $timeoday = shift;
  return sub { print "Good $timeoday\n" };
}

my $greeter = make_greeter("morning");
$greeter->();

# if you pass a subrouine off to some other code, 
# which promises to CALL that subroutine BACK 
# at some later point in time / when some event happens, 
# you have what's called a callback.
# Depending on the calling code, 
# the callback might or might not receive arguments.

sub handle_get_response {
  my $response = shift;
  # ...
}

my $get_response_handler = \&handle_get_response;

# When the request is done SomeWebClient will call $get_response_handl
+er->();
SomeWebClient->get( url => $get_response_handler );
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.