#!/usr/bin/perl
# (c) 2001 Vlado Keselj <vkeselj@cs.uwaterloo.ca>
#
# Print leaves of the trees given a forest.
# (Standard tree formats, e.g. Penn TreeBank.)
#
# Example: on input:
#   (S (N I) (V code) (. .))
#   (S (N You)
#      (V code)
#      (. .))
#
# produces:
#   I code . 
#   You code .

$CurrentToken='START';
scan();
while ( $CurrentToken ne '') {
    doTree();
    print "\n";
}

sub scan {
  scanBegin:
    return '' if $CurrentToken eq '';
    if (! $CurrentLine) { $CurrentLine = <>; }
    if (! $CurrentLine) { $CurrentToken=''; return ''; }
    $CurrentLine =~ s/^\s+//;
    if (! $CurrentLine ) { goto scanBegin; }
    if ($CurrentLine =~ /^(\(|\))\s*/) {
	$CurrentToken = $1;
	$CurrentLine = $';
    }
    else {
	$CurrentLine =~ /^([^\s()]+)\s*/ or die;
	$CurrentToken = $1; $CurrentLine = $';
    }
    return $CurrentToken;
}

sub doTree {
    if ($CurrentToken eq '(') {
	scan(); die if $CurrentToken eq '';
	if ($CurrentToken ne '(') { scan(); }
	do { doTree(); die if $CurrentToken eq ''; }
	while ($CurrentToken ne ')');
	scan();
    }
    else {
	print "$CurrentToken ";
	scan();
    }
}