-module(engine3).
-compile([export_all]).

events() -> [{m1, ok}, {m2, ok}].

p({m1, ok}) -> 0.2;
p(A) when is_tuple(A) -> none.

cp({m2, ok}, {m1, ok}) -> 0.8;
cp(_, _) -> none.

getp({A, B}) when is_tuple(A), is_tuple(B) ->
     case cp(A, B) of
        none ->
            Pba = cp(B, A),
            Pa = getp(A),
            Pb = getp(B),
            Pba * Pa / Pb;
        X ->
            X
     end;

getp(A) when is_tuple(A) ->
	case p(A) of
	  none ->
		lists:sum([ getp({A, B})*getp(B) || B <- events(), p(B) /= none, cp(A,B) /= none ]);
	  X ->
	      X
	end.