ErlangでMMOとか作ろう

Erlang Super Liteの宿題が「Erlang Programming」Chapter 3 Ex3.8ですが、ようやくひととおりの機能がまとまりました。

というわけで、以下、3.8の実装案です。


-module(exercise).
-compile(export_all).

%---------------------------------------

evaluator(Exps) ->
evaluator_acc(Exps).

evaluator_acc({plus, Param1, Param2}) ->
evaluator_acc(Param1) + evaluator_acc(Param2);

evaluator_acc({minus, Param1, Param2}) ->
evaluator_acc(Param1) - evaluator_acc(Param2);

evaluator_acc({multi, Param1, Param2}) ->
evaluator_acc(Param1) * evaluator_acc(Param2);

evaluator_acc({divide, Param1, Param2}) ->
evaluator_acc(Param1) / evaluator_acc(Param2);

evaluator_acc({num, Param1}) ->
Param1.

%---------------------------------------

simplifier({Op, Param1, Param2}) ->
EP1 = evaluator(Param1),
EP2 = evaluator(Param2),
case evaluator({Op, Param1, Param2}) of
EP1 -> Param1;
EP2 -> Param2;
1 -> {num, 1};
0 -> {num, 0};
_-> {Op, simplifier(Param1), simplifier(Param2)}
end;

simplifier({num, Param1}) ->
{num, Param1}.


%---------------------------------------

remove_top_brace(ExpChars) ->
[H|T] = ExpChars,
case H of
40 ->
[HH|TT] = lists:reverse(T),
case HH of
41 -> lists:reverse(TT);
_ ->ExpChars
end;
_-> ExpChars
end.

pp(Exps) ->
remove_top_brace(lists:flatten(pp_acc(Exps))).

pp_acc({plus, Param1, Param2}) ->
[ "(" , pp_acc(Param1), "+" , pp_acc(Param2), ")"];

pp_acc({minus, Param1, Param2}) ->
[ "(" , pp_acc(Param1), "-" , pp_acc(Param2), ")"];

pp_acc({multi, Param1, Param2}) ->
[ "(" , pp_acc(Param1), "*" , pp_acc(Param2), ")"];

pp_acc({divide, Param1, Param2}) ->
[ "(" , pp_acc(Param1), "/" , pp_acc(Param2), ")"];

pp_acc({num, Param1}) ->
io_lib:format("~p", [Param1]).


%---------------------------------------

compile({simplify, Exps}) ->
lists:flatten(compile_acc(simplifier(Exps), []));

compile(Exps) ->
lists:flatten(compile_acc(Exps, [])).

compile_acc({Op, Param1,Param2}, Stack) ->
[ compile_acc(Param2, Stack), compile_acc(Param1, Stack), {op, Op} | Stack];

compile_acc({num, Param1}, Stack) ->
[{num, Param1} | Stack].


%---------------------------------------

run(OpStack) ->
[Result | T] = run_acc(OpStack, []),
Result.

run_acc([], DataStack) ->
DataStack;

run_acc([H | T], DataStack) ->
NewDataStack = operate(H, DataStack),
run_acc(T, NewDataStack).

operate({num, Param}, DataStack) ->
[Param | DataStack];

operate({op, plus}, DataStack) ->
[Param1, Param2 | T] = DataStack,
[ Param1 + Param2 | T];

operate({op, minus}, DataStack) ->
[Param1, Param2 | T] = DataStack,
[ Param1 - Param2 | T];

operate({op, multi}, DataStack) ->
[Param1, Param2 | T] = DataStack,
[ Param1 * Param2 | T];

operate({op, divide}, DataStack) ->
[Param1, Param2 | T] = DataStack,
[ Param1 / Param2 | T].