package Machine;

##  new (nil) : Machine_ref
#
#   trivial constructor
#
sub new {
    my $self = bless {}, shift;
    return ($self);
}

##  execute
#
#   run through the list of commands, halting when one of them fails
#
sub execute {
    my $self  = shift;
    my $model = shift;
    
    for $cmd (@{ $self->_get_commands() }) {            # [1]
    last if ( 0 == $cmd->execute ($model) );            # [2]
    }
    return();
}
###
# [1] iterate over the list of Command objects that belongs to the 
#     specific Machine, executing each one in turn.
# [2] drop out of the loop if any Command in the sequence returns
#     a zero.
#
#   in practice, this is equivalent to executing a set of
#   short-circuit conditionals:
#
#       if (<condition 1>) { return ('value 1') }
#       if (<condition 2>) { return ('value 2') }
#       if (<condition 3>) { return ('value 3') }
#
#   but it's cleaner, and you can make each Command much more complex
#   than the body of a sensible conditional.
###

##  STATE-SPECIFIC OPERATIONS 

##  _get_commands (nil) : listref
#
#   each Machine has its own list of Commands that should be 
#   executed in response to the user's input.   this routine returns 
#   a reference to that list.
#
sub _get_commands {
    return ([]);
}


1;