#### Method: param
# Returns the value(s)of a named parameter.
# If invoked in a list context, returns the
# entire list.  Otherwise returns the first
# member of the list.
# If name is not provided, return a list of all
# the known parameters names available.
# If more than one argument is provided, the
# second and subsequent arguments are used to
# set the value of the parameter.
####
sub param {
    my($self,@p) = self_or_default(@_);
    return $self->all_parameters unless @p;
    my($name,$value,@other);

    # For compatibility between old calling style and use_named_parameters() style, 
    # we have to special case for a single parameter present.
    if (@p > 1) {
	($name,$value,@other) = rearrange([NAME,[DEFAULT,VALUE,VALUES]],@p);
	my(@values);

	if (substr($p[0],0,1) eq '-') {
	    @values = defined($value) ? (ref($value) && ref($value) eq 'ARRAY' ? @{$value} : $value) : ();
	} else {
	    foreach ($value,@other) {
		push(@values,$_) if defined($_);
	    }
	}
	# If values is provided, then we set it.
	if (@values) {
	    $self->add_parameter($name);
	    $self->{$name}=[@values];
	}
    } else {
	$name = $p[0];
    }

    return unless defined($name) && $self->{$name};
    return wantarray ? @{$self->{$name}} : $self->{$name}->[0];
}