Erlang recursion examples

func.erl

-module(func).

-export([fac/1, ft/1, len/1, lt/1, fib/1, tail_fib/1]).

%% basic recursive implementation of factorial
fac(N) when N == 0 -> 1;
fac(N) when N > 0 ->
    N*fac(N-1).

%% Tail recursion implementation of factorial
ft(N) -> ft(N, 1).

ft(0, Acc) -> Acc;
ft(N, Acc) when N > 0 ->
    ft(N-1, N*Acc).

%% List lenght recursive implementation
len([]) -> 0;
len([_]) -> 1;
len([_|T]) -> 1 + length(T).

%% List length tail recursion implementation
lt(L) -> lt(L, 0).

lt([], _) -> 0;
lt([_], Acc) -> Acc + 1;
lt([_|T], Acc) -> lt(T, Acc + 1).

%% Fibonacci numbers
fib(0) -> 0;
fib(1) -> 1;
fib(N) -> fib(N-1) + fib(N-2).

%% Fibonacci tail recursive implementation
tail_fib(0) -> 0;
tail_fib(1) -> 1;
tail_fib(N) -> tail_fib(N-2, 1, 0).

tail_fib(0, A, B) -> A + B;
tail_fib(N, A, B) -> tail_fib(N-1, A+B, A).