# Produce string representation of a hash whose ref is given as the
# first parameter.
# other parameters are options:
#  --email-style  - email headers style
#  --key-order=k1,k2... - key order (other keys are alphabetically
# appended)
#
# Union and intersection subroutines required.
#
sub toString($@) {
    my $x = shift;
    my $emailstyle = '';
    my @keyorder = ();
    while (@_) {
        my $o = shift;
        if ($o eq '--email-style') { $emailstyle = 1 }
        elsif ($o =~ /^--key-order=/) { @keyorder = split(',', $') }
        else { die "unknown option:$o" }
    }

    my $r;
    if (ref($x) eq "HASH") {
        my @keys =
            intersection( [union(@keyorder, sort(keys(%{ $x })))],
                          [keys(%{ $x })] );

	if (not @keys) {
	    return "{ }" unless $emailstyle;
	    die "don't know how to represent empty hash in email style";
	}

        if (not $emailstyle) { $r = "{\n" }
        foreach my $k (@keys) {
            my $v = $x->{$k};
            if ($emailstyle) { $r .= "$k:$v\n" }
            else {
                $k =~ s/\\/\\\\/g; $k =~ s/'/\\'/g;
                $v =~ s/\\/\\\\/g; $v =~ s/'/\\'/g;
                $r .= "  '$k' => '$v',\n";
            }
        }
	$r =~ s/,\n$/\n}\n/;
        return $r;
    }
    else { die "not yet implemented ref=: ".ref($x) }
}