Actually, that code isn't doing what you think. One way to see is to just add "use strict" to it. You'll get: Global symbol "$x" requires explicit package name

A more fun way is: 

sub foo {
    my $x= $_[0]   if  ! defined $x;
    print "(@_):", ++$x, " ";
    undef $x   if  @_  &&  shift;
}
foo($_) for( 0,0,5,4,3,0,5,0,4,0,3 );
print $/, $x= 10, $/;
foo($_) for( 0,0,5,4,3,0,5,0,4,0,3 );
print $/;

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which produces: 
(0):1 (0):1 (5):6 (4):5 (3):4 (0):1 (5):6 (0):1 (4):5 (0):1 (3):4
10
(0):1 (0):2 (5):3 (4):1 (3):1 (0):1 (5):2 (0):1 (4):2 (0):1 (3):2

[download]
The $x in "if !defined $x" is the global $main::x because my variables can't be used until after the end of the statement in which they were declared.

So your code is always initializing the lexical $x in your subroutine because you have never defined the global $main::x that you are checking against.

        - tye (but my friends call me "Tye")

In reply to (tye)Re2: Unusual Closure Behaviour by tye
in thread Unusual Closure Behaviour by tachyon

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