Source code in the picat programming language

go ?=>
  println("\nEnd terms with '.'.\n'quit.' ends the session.\n"),
  Prev = findall(P,beats(P,_)),
  ChoiceMap = new_map([P=0 : P in Prev]),
  ResultMap = new_map([computer_wins=0,user_wins=0,draw=0]),
  play(Prev,ChoiceMap,ResultMap),
  nl,
  println("Summary:"),
  println(choiceMap=ChoiceMap),
  println(resultMap=ResultMap),
  nl.
  
go => true.

%
% Play an interactive game.
%
play(Prev,ChoiceMap,ResultMap) =>
  print("Your choice? "),
  P = read_term(),
  if P == quit then
    nl,
    print_result(ResultMap)
  else
    C = choice(ChoiceMap),
    printf("The computer chose %w%n", C),
    result(C,P,Prev,Next,Result),
    ChoiceMap.put(P,ChoiceMap.get(P)+1),
    ResultMap.put(Result,ResultMap.get(Result,0)+1),
    play(Next,ChoiceMap,ResultMap)
  end.

%
% Do a weighted random choice based on the user's previous choices.
%
weighted_choice(Map) = Choice =>
  Map2 = [(V+1)=K : K=V in Map].sort, % ensure that all choices can be made
  % Prepare the probability matrix M
  Total = sum([P : P=_ in Map2]),
  Len = Map2.len,
  M = new_array(Len,2),
  T = new_list(Len),
  foreach({I,P=C} in zip(1..Len,Map2))
    if I == 1 then
      M[I,1] := 1,
      M[I,2] := P
    else
      M[I,1] := M[I-1,2]+1,
      M[I,2] := M[I,1]+P-1
    end,
    T[I] := C
  end,
  M[Len,2] := Total,

  % Pick a random number in 1..Total
  R = random(1,Total),
  Choice = _,
  % Check were R match
  foreach(I in 1..Len, var(Choice))
    if M[I,1] <= R, M[I,2] >= R then
      Choice := T[I]
    end
  end.

%
% Check probably best counter choice.
%
choice(Map) = Choice =>
  % what is the Player's probably choice
  PlayersProbablyMove = weighted_choice(Map),
  % select the choice that beats it
  beats(Choice,PlayersProbablyMove).


print_result(ResultMap) =>
  foreach(C in ResultMap.keys)
    println(C=ResultMap.get(C))
  end,
  nl.

% This part is from the Prolog version.
result(C,P,R,[C|R],Result) :-
  beats(C,P),
  Result = computer_wins,
  printf("Computer wins.\n").
result(C,P,R,[B|R],Result) :-
  beats(P,C),
  beats(B,P),
  Result=user_wins,
  printf("You win!%n").
result(C,C,R,[B|R],Result) :-
  beats(B,C),
  Result=draw,
  printf("It is a draw\n").

beats(paper, rock).
beats(rock, scissors).
beats(scissors, paper).