Rock, paper, scissors game definition

rps.erl

-module(rps).

-export([beats/1]).

-export([result/2]).

-export([tournament/2]).

beats(rock)     -> scissors;
beats(paper)    -> rock;
beats(scissors) -> paper.

result(X, Y) ->
    case {beats(X), beats(Y)} of
        {Y, _} -> win;
        {_, X} -> lose;
        _      -> draw
    end.

points(X, Y) ->
    result2points(result(X, Y)).

result2points(win)  -> 1;
result2points(draw) -> 0;
result2points(lose) -> -1.

tournament(L1, L2) ->
    lists:sum(lists:zipwith(fun points/2, L1, L2)).