Basic implementation of infinite series in Erlang, take, filter and nth.

infinite.erl

-module(infinite).
-compile(export_all).

%%% Usage
%
%   Ints = infinite:stream(0, fun (X) -> X + 1 end).
%
%   % Numbers from 0 to 9
%   infinite:take(Ints, 10).
%
%   % Even numbers only
%   infinite:filter(Ints, fun (X) X rem 2 == 0).
%
%   % Nth element of a series
%   infinite:nth(Ints, 10).

stream (Init, F) ->
  fun() -> { Init, stream(F(Init), F) } end.

take (_,0) -> [];
take (S, N) ->
  {X,Next} = S(),
  [X|take(Next, N - 1)].

filter (S, P) ->
  fun () ->
      {X,UnfilteredNext} = S(),
      FilteredNext = filter(UnfilteredNext, P),
      case P(X) of
        true  -> {X,FilteredNext};
        false -> FilteredNext()
      end
  end.

nth (S, 1) ->
  {X,_} = S(), X;
nth (S, N) ->
  {_,Next} = S(), nth(Next, N - 1).