Code for scoring a bowling game.

game.erl

-module(game).
-export([score/1]).


score(Rolls) -> frame(1, 0, Rolls).

%% frame/3 takes Frame #, Score accumulator, and list of remaining Rolls.
%%   It tail-recurses to the next frame with an updated Score and Rolls list.

%% Game complete.
frame(11, Score, _BonusRolls) -> Score;
%% Strike.
frame(Frame, Score, [10|Rest]) ->
    [Bonus1, Bonus2|_] = Rest,
    frame(Frame + 1, Score + 10 + Bonus1 + Bonus2, Rest);
%% Bad input.
frame(_Frame, _Score, [First,Second|_Rest]) when (First + Second > 10) -> err;
%% Spare.
frame(Frame, Score, [First,Second|Rest]) when (First + Second == 10) ->
    [Bonus1|_] = Rest,
    frame(Frame + 1, Score + 10 + Bonus1, Rest);
%% Normal.
frame(Frame, Score, [First,Second|Rest]) ->
    frame(Frame + 1, Score + First + Second, Rest).

This is the original version, with almost no error checking. It barfs on incomplete games. The latest version with full error handling is at https://github.com/bluegraybox/examples/blob/master/bowling/erlang/game.erl