Using this definition of closure, every procedure or sub you write is a closure.

I don't think using this broad a definition helps clarify the term or how closures are used in Perl. Within Perl at least, the term "closure" refers to a subroutine that references lexical variables outside it's own scope. This has a very specific meaning and a very specific application. 

# doesn't reference anything outside the scope of the subroutine scope

sub not_a_closure {
  my $i;
  $i++;
  return $i
}

# references a package variable, not a lexical variable

our $global;
sub also_not_a_closure {
  $global++;
  return $global;
}

# a closure -- references a lexical outside the scope

my $lexical;
sub a_closure {
  $lexical++;
  return $lexical;
}

# anonymous closure generator -- references a new variable each time

sub closure_generator {
  my $fresh_lexical;
  return sub {
    $fresh_lexical++;
    return $fresh_lexical;
  }
}

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-xdg

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In reply to Re^2: Nailing down closures! by xdg
in thread Nailing down closures! by mattford63

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