f(1) ->
    io:format("I got one!");
f(X) when X rem 2 == 0 ->
    io:format("I got even!");
f(X) when X rem 2 == 1 ->
    io:format("I got odd! (but not one)").

...

f(random:uniform(1000)).
f("Now eat this!").  %% runtime error

##</code><code>##

-module(fns).
-export([run_test/0]).

f(X, Acc) when X rem 2 == 0 ->
    Acc;
f(X, Acc) when X rem 2 == 1 ->
    Acc + 1.

run_test() ->
    TSeq = [random:uniform(10) ||
            _ <- lists:seq(1, 1000000)],
    {Time, Result} = timer:tc(fun() ->
             lists:foldl(fun f/2, 0, TSeq)
                              end),
    io:format("~w microseconds~nResult: ~w~n",
              [Time, Result]).

##</code><code>##

93267 microseconds
Result: 500464