RPG/MMORPG/MUD Item handling ideas

item.erl

-module(item).

-export([gen_shield/0]).
-export([transmogrify/2, as_item/1]).
-export([weapon_damage/1, look/1]).

-record(item, {
	  %% Rather arbitrary identity
	  id :: term(),
	  %% Proplist of items properties
	  properties :: [{atom(), term()}]}).

gen_shield() ->
    Desc = "A spiked and very sturdy looking tower shield",
    Damage = {6,d,6},
    ArmorRating = 16,
    #item { id = {shield, 37},
	    properties = [{as_weapon, Damage},
			  {description, Desc},
			  {as_armor, ArmorRating}]}.

%% This is a neat trick in a functional language. The representation of the
%% item at hand can change view depending on who needs to look at
%% it. This way, transmogrifying the object into something else makes
%% it suitable to use when viewed in a specific way.
%%
%% If we don our weapon-eyeglasses, then it is a weapon all of a sudden:
transmogrify(Ty, #item { id = Id, properties = Props } = I) ->
    %% This can also be a call directly to a submodule:
    %% Ty:create(Id, Props)
    case Ty of
	weapon ->
	    {weapon, Id, I,
	     proplist:get_value(description, Props),
	     proplist:get_value(as_weapon, Props)};
	armor ->
	    {armor, Id, I,
	     proplist:get_value(description, Props),
	     proplist:get_value(as_armor, Props)}
    end.

%% Of course, there is a way to bring back the general view
as_item({weapon, I, _, _}) -> I;
as_item({armor,  I, _, _}) -> I.

%% This should reside in a weapon:damage function inside the weapon module
%% in a real solution
weapon_damage({weapon, _Id, _Desc, Damage}) -> Damage.

%% Generic, polymorphic, function to look at an object.
look(#item { properties = Ps }) ->
    proplists:get_value(description, Ps);
look({weapon, _, Desc, _}) -> Desc;
look({armor , _, Desc, _}) -> Desc;
%% Not specific? Look up the module that knows how to act on it and
%% call it
look(Tup) when is_tuple(Tup) ->
    Ty = element(1, Tup),
    Ty:look(Tup).