Say you have a complicated method and you want to have an embedded subroutine there, that won't be visible elsewhere - like Pascal or D allow. No problem - you make a lexical code reference:

my $func = sub {
    my ($param1, $param2) = @_;
    do { foo };
    return $bar;
}
[download]

Then you call this subroutine like this:

But what if you want this subroutine to be recursive? Inside its body, the $func variable isn't defined yet (right hand side of assignment is evaluated first), so you can't just say

my $func = sub {
    do { something };
    $func->($param1, $param2);
}
[download]

The solution is obvious - you have to add a parameter to the function where you'll pass itself:

my $func = sub {
    my ($func, $param1, $param2) = @_;
    do { something };
    $func->($func, $param1, $param2);
}
[download]

Of course you'll then have to adapt the first call as well: