package main;

# ...
my $command;
eval {
	$command = CommandFactory->create ($input_string); # returns the right subclass of Command
}; #trap non-existent commands
if ($@) {printandprompt("command not recognized");}

if ($command->parse_syntax) { # check for syntax errors
	eval {
		$command->execute;
	}; # trap semantic errors, e.g. "user doesn't exist"
	if ($@) {
		print $@; # maybe die if need be
	}
} else {
	printandprompt $command->syntax_string;
}

package CommandFactory;

sub create {
	my $class = shift;
	my $str = shift;
	
	my ($cmd, @args) = split $str;
	my $cmd_class = "Command::" . ucfirst ($cmd);
	return $cmd_class->new(@args);
}

package Command;

use vars qw/$SYNTAX/;
# ...
sub new {
	my $class = shift;
	my @args = @_;
	
	my $self = {args => \@args};
	bless $self, $class;
}

sub _syntax {
	my $self = shift;

	no strict 'refs';
	my $class = ref ($self) || $self;
	return ${"$class::SYNTAX"};
}

sub parse_syntax {
	my $self = shift;

	# check $self->{args} against $self->_syntax
	# then parse the arguments into $self fields
	# return false on error
	# alternatively "die" and catch the exception
}

package Command::Msg;

use Command;
use base 'Command';
use vars qw/$SYNTAX/;

$SYNTAX = {
	options => {
		player => {
			required 	=> 1,
			arg		=> 'string',
		}
		loudness => {
			required 	=> 0,
			arg		=> 'int'
		}
	}
	arguments => {
		min => 1,
	}
};

sub execute {
	my $self = shift;
	
	# send $self->{msg} to $self->{player} with $self->{loudness}
}