my $node = my $tree = [];
my @stack;

##</code><code>##

if ($token eq '(') {
  push @{ $node }, [];
  push @stack, $node;
  $node = $node->[-1];  # the new empty array ref
}

##</code><code>##

if ($token eq ')') {
  $node = pop @stack;
}

##</code><code>##

$a = $b = [];
$a = 2;

##</code><code>##

#!/usr/bin/perl -w

use File::Find;
use Data::Dumper;
use strict;

$Data::Dumper::Indent = 1;

build_tree(my $tree, shift);
print Dumper $tree;


{ 
  sub build_tree {
    my $node = $_[0] = {};
    my @s;
    find( sub {
      # fixed 'if' => 'while' -- thanks Rudif
      $node = (pop @s)->[1] while @s and $File::Find::dir ne $s[-1][0];
      return $node->{$_} = -s if -f;
      push @s, [ $File::Find::name, $node ];
      $node = $node->{$_} = {};
    }, $_[1]);
    $_[0]{$_[1]} = delete $_[0]{'.'};
  }
}