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


-module(monad_test).

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

%% ====================================================================
%% API functions
%% ====================================================================
-export([continuation/1]).

%bind(nothing, _C) -> nothing;
%bind(F, C) -> C(F).

%bind(F, C) -> fun(nothing) -> nothing; (A) -> C(F(A)) end.

bind({error, State}, _) -> {error, State};
bind(F, C) -> 
  fun
    ({error, State}) -> {error, State};
    ({_Status, State}) -> C(F(State)) 
  end.
return() -> fun(X) -> X end.

%% continuation([f1, f2, f3]) ->
%%   bind(f1, 
%%            bind(f2, 
%%                     bind(f3, 
%%                               return)
%%                )
%%       )
%% . return() == fun() -> f3(2)(S)

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

f_test() ->
  Cont = continuation([add(5),sub(3),mult(2)]),
  io:format(user, "Result = ~p~n~n", [Cont({2,0})]),
  io:format(user, "Result = ~p~n~n", [Cont({-6,0})]),
  Cont1 = continuation([add(5),sub(-3),mult(2)]),
  io:format(user, "Result = ~p~n~n", [Cont1({2,0})]),
  Cont2 = continuation([add(5),sub(3),mult(0)]),
  io:format(user, "Result = ~p~n~n", [Cont2({2,0})])
%%   io:format(user, "Result = ~p~n~n", [Cont(3)])
.
%% ====================================================================
%% Internal functions
%% ====================================================================

add(A) -> fun(State) ->
  io:format(user, "add >>> Status:~p State:~p~n", [A, State]),
  case A of
    A when A < 0 -> {error, State};
    _ -> {ok, State + A}
  end
end.

sub(A) -> fun(State) ->
  io:format(user, "sub >>> Status:~p State:~p~n", [A, State]),
  case A of
    A when A < 0 -> {error, State};
    _ -> {ok, State - A}
  end
end.

mult(A) -> fun(State) ->
  io:format(user, "mult >>> Status:~p State:~p~n", [A, State]),
  case A of
    A when A == 0 -> {error, State};
    _ -> {ok, State * A}
  end
end.