}
    
    close (ESE);
}
#-------------------------------------------------------------------------------
sub get_dependencies {

    # create pattern to match any left values
    my $pattern = "";
    foreach my $lvar (keys %expressions) {
	$pattern = "$pattern|$lvar";
    }
    # strip initial |
    $pattern =~ s!\|(.*)!/$1/!;	# var1|var2|var3
    print "$pattern\n" if $debug;

    # compile the pattern to improve speed
    my $regexp = qr/($pattern)/;

    # compare the pattern to each expression
    foreach my $lvar (keys %expressions) {
	$dependencies{$lvar} = "";
	$_ = $expressions{$lvar};
	for my $lvar2 (keys %expressions) {
	while (/$regexp/g) {
	    # a left value has been found in the expression
	    # add it to the dependencies for this lvar
	    $dependencies{$lvar} = "$dependencies{$lvar} $1";
	    if ($expressions{$lvar} =~ /$lvar2/) {
		# a left value has been found in the expression
		# add it to the dependencies for this lvar
		$dependencies{$lvar} = "$dependencies{$lvar} $lvar2";
	    }
	}
	print "$lvar:\t$dependencies{$lvar}\n" if $debug;
    }
}
#-------------------------------------------------------------------------------
sub write_make {