Austral

-- A number guessing game.
module Guess is
    -- We need to import the `Random` module to generate random numbers, and the
    -- `IO` module to print to the screen and read from the keyboard.
    import Standard.Random (RandomState, random_int_in_range);
    import Standard.IO (print_line, read_line);
    import Standard.Integer (parse_int);
    import Standard.Memory (free);
    import Standard.String (String);
    import Standard.Error (handle_error);

    -- The entrypoint of the program.
    generic [R: Region]
    function main(): ExitCode is
        -- Create a new random number generator state.
        let state: RandomState := RandomState();
        -- Generate a random integer between 1 and 100.
        let secret: Int64 := random_int_in_range(state, 1, 100);
        -- Free the random state, we don't need it anymore.
        free(state);
        print_line("I'm thinking of a number between 1 and 100.");
        -- Start the game loop.
        return game_loop(secret);
    end;

    -- The game loop.
    generic [R: Region]
    function game_loop(secret: Int64): ExitCode is
        loop
            print_line("Take a guess: ");
            -- Read a line from the user.
            let line: String[R] := read_line();
            -- Try to parse the line as an integer.
            let maybe_guess: Either[Int64, String[R]] := parse_int(line);
            case maybe_guess of
                when Left(let guess: Int64) do
                    if guess < secret then
                        print_line("Too low.");
                    else if guess > secret then
                        print_line("Too high.");
                    else
                        print_line("You win!");
                        return ExitSuccess();
                    end if;
                end;
                when Right(let err: String[R]) do
                    print_line("Error: not a valid integer.");
                    handle_error(err);
                end;
            end case;
        end loop;
    end;