Recursive exercise

recursive.erl

-module(recursive).

-export([fib/1,pieces/1]).

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

%Steep by steep evaluation:
%fib(4) -> fib(2) + fib(3)
%fib(4) -> (fib(0) + fib(1)) + (fib(1) + fib(2))
%fib(4) -> (0 + 1 + 1 + (fib(0) + fib(1))
%fib(4) -> (0 + 1 + 1 + 0 + 1).


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