gistfile1.txt

%% Naive factorial, not tail recursive
%% (caveat, not tested)

fac(0) -> 1;
fac(N) when is_integer(N), N > 0 ->
  RecCall = fac(N-1), %% The recursive call is not the last thing that happens
  RecCall * N. % This is the last thing that happens

%% Tail recursive variant:

tfac(N) -> tfac(N, 1).

tfac(0, Acc) -> Acc;
tfac(N, Acc) when is_integer(N), N > 0 ->
  tfac(N-1, Acc * N). %% Here the call is tail recursive.