Hm. The Erlang people talk of "Pattern matching in function head and in case and receive clauses are optimized by the compiler." & "the compiler is free to rearrange the clauses. It will generate code similar to this".
Of course it's optimized. Like you would expect from a language where the only way to loop is recursion.

Yet, this works in Erlang:

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

[download]
Just for comparison (with Perls): 
-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]).

[download]
output: 
93267 microseconds
Result: 500464

[download]
So, functions that actually do something in Erlang (count odd numbers) are three times faster then Perls functions that do nothing whatsoever.

In reply to Re^9: rough approximation to pattern matching using local (Multi Subs) by Anonymous Monk
in thread rough approximation to pattern matching using local by gregory-nisbet

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