#!/usr/local/bin/perl -w
use Getopt::Std;

sub usage { <<EOM;
Usage: $0 file1 [file2]
	Interleaves trees of file1 with those of file2 (or stdin)
EOM
}

my %opt;
getopts ('h', \%opt);

if ($opt{h}) { die usage(); }
if (@ARGV < 1) { die usage(); }

my $infile1 = shift;
open (IN1, $infile1) or die "Can't open file $infile1, aborting";

my $curtree1 = "";
my $curtree2 = "";

while (!eof IN1) {
  while (<IN1>) {
    if (/^\(/) {
      print $curtree1;
      $curtree1 = $_;
      last;
    }
    $curtree1 .= $_;
  }
  while (<>) {
    if (/^\(/) {
      print $curtree2;
      $curtree2 = $_;
      last;
    }
    $curtree2 .= $_;
  }
}

print $curtree1;
print $curtree2;
