use strict;
use warnings;

while(my $input = <DATA>){
  print "input: $input\n";
  my $level  = 0;
  my $tab    = "| ";
  my %action = (
		'('       => sub { print "\n", $tab x ++$level, shift },
		')'       => sub { print "\n", $tab x $level--, shift },
		'default' => sub { print shift },
	       );
  
  ( $action{$_} // $action{'default'} )->($_) for $input =~ /./g;
  print "\n\n\n";
}

__DATA__
A (B C D)
A (B C D) (E F G)
A B (C (D E) (F G)) (H I)