2nd week of Erlang on FutureLearn (2.3)

fourth.erl

-module fourth.
-export[fac/1,fib/1,pieces/1].

fac(0) ->
   1;
fac(N) when (N > 0) ->
   fac(N - 1) * N
.

fib(0) ->
   0;
fib(1) ->
   1;
fib(N) when (N > 0) ->
   fib(N - 2) + fib(N - 1)
.

% Step through of 'fib(4)':
% __fib(4)
% = fib(2) + fib(3)
% = (fib(0) + fib(1)) + (fib(1) + fib(2))
% = (0 + 1) + (1 + (fib(0) + fib(1)))
% = 1 + 1 + (0 + 1)
% = 1 + 1 + 1
% = 3

pieces(0) ->
   1;
pieces(N) when (N > 0) ->
   N + pieces(N-1)
.