Flatten algorithm on Erlang.

util.erl

%%
%% Util module which contains a simple 'flatten list' 
%% implementation which is not fastest but most comprehent.
%%
-module(util).

-export([flatten/1]).

%% Flatten empty list is an empty list.
flatten([]) ->
    [];
%% If the first element of a list is an also list then 
%% flatten that element and concatinate with the flattened tail.
flatten([L|Tail]) when is_list(L) ->
    flatten(L) ++ flatten(Tail);
%% If the first element is not a list then just cons that element with the flattened tail.
flatten([E|Tail]) ->
    [E|flatten(Tail)].