%% @author alexeikrasnopolski
%% @doc @todo Add description to monad_test.


-module(maybe_monad_2_test).

-include_lib("eunit/include/eunit.hrl").

%% ====================================================================
%% API functions
%% ====================================================================
-export([continuation/1, f1/1, f2/1, f3/1]).

bind(nothing, _C) -> nothing;
bind(F, C) -> C(F).
return() -> fun(A) -> A end.
  
%% continuation([f1, f2, f3]) ->
%%   bind(f1, 
%%            bind(f2, 
%%                     bind(f3, 
%%                               return)
%%                )
%%       ) == 
%% .

%% continuation([f1, f2, f3]) ->
%%   fun(X) -> bind(f1(X), continuation(f2, f3)) end.
%%   fun(X) -> bind(f1(X), fun(Y) -> bind(f2(Y), continuation(f3)) end) end.
%%   fun(X) -> bind(f1(X), fun(Y) -> bind(f2(Y), fun(Z) -> bind(f3(Z), continuation([])) end) end) end.
%%   fun(X) -> bind(f1(X), fun(Y) -> bind(f2(Y), fun(Z) -> bind(f3(Z), return()) end) end) end.

%%   fun(X) -> bind(f1(X), fun(Y) -> bind(f2(Y), fun(Z) -> bind(f3(Z), return()) end) end) end.
%%   fun(X) -> fun(f1(X)) -> bind(f2(f1(X)), fun(Z) -> bind(f3(Z), return()) end) end end.
%%   fun(X) -> bind(f2(f1(X)), fun(Z) -> bind(f3(Z), return()) end) end.
%%   fun(X) -> fun(f2(f1(X))) -> bind(f3(f2(f1(X))), return()) end end.
%%   fun(X) -> bind(f3(f2(f1(X))), return()) end.
%%   fun(X) -> bind(f3(f2(f1(X))), fun(A) -> A end) end.
%%   fun(X) -> fun(f3(f2(f1(X)))) -> f3(f2(f1(X))) end end.
%%   fun(X) -> f3(f2(f1(X))) end.
%%   f3(f2(f1(X))).

continuation([]) -> return();
continuation([F | RF]) ->
  fun(A) -> bind(F(A), continuation(RF)) end.

f_test() ->
  Cont = continuation([fun f1/1,fun f2/1,fun f3/1]),
  io:format(user, "*** Result = ~p~n~n", [Cont(0)]),
  io:format(user, "*** Result = ~p~n~n", [Cont(1)]),
  io:format(user, "*** Result = ~p~n~n", [Cont(2)]),
  io:format(user, "*** Result = ~p~n~n", [Cont(3)]).

%% ====================================================================
%% Internal functions
%% ====================================================================

f1(A) ->
  io:format(user, "f1 >>> ~p~n", [A]),
  case A of
    3 -> nothing;
    _ -> A + 1
  end.

f2(A) ->
  io:format(user, "f2 >>> ~p~n", [A]),
  case A of
    3 -> nothing;
    _ -> A + 1
  end.

f3(A) ->
  io:format(user, "f3 >>> ~p~n", [A]),
  case A of
    3 -> nothing;
    _ -> A + 1
  end.