Excercises for https://www.futurelearn.com/courses/functional-programming-erlang/1/steps/151655#fl-comments

tail.erl

%%%-------------------------------------------------------------------
%%% @author josh
%%% Created : 25. Feb 2017 10:44 AM
%%%-------------------------------------------------------------------
-module(tail).
-author("josh").
-export([fib/3, fib/1, loop/1, perfect/1, lp/1]).

%Hmm..there seems to be a bug in this one.
fib(N) -> fib(N,0,1).

fib(0,N1,N2) -> N1 + N2;
fib(N, N1, N2) when N>0 ->
  fib(N-1, N2, N1 + N2).


loop(N) when N>0 ->
  io:format("~p~n", [N]),
  loop(N-1);
loop(0) ->
  io:format("bye~n").

% Test cases: 6, 28, 496, 8128, and 33550336
perfect(N) ->
  N == perfect(N,1,0).

perfect(N,D,ACC) when D>N/2 ->
  ACC;
perfect(N,D,ACC) when (N rem D) == 0 ->
  perfect(N, D+1, ACC + D);
perfect(N,D,ACC) ->
  perfect(N, D+1, ACC).


%BONUS: find perfect numbers in the first N integers
io(N, X) when X ->io:format("Perfect: ~p~n",[N]);
io(_,_) -> false.

lp(N) -> lp(N,perfect(N)).

lp(N, X) when N>0 ->
  io(N,X),
  lp(N-1, perfect(N-1));
lp(0,_) ->
  io:format("bye~n").