Elixir streams should have a "pure" version that automatically memoizes the result (aka lazy lists). E.g.
s = PureStream.map([1, 2, 3], fn x -> x + 1 end) Enum.to_list(s) # lazily computes => [2, 3, 4] Enum.to_list(s) # returns [2, 3, 4] *but* no new computation is done because we already did the computation and memoized it They could allow the caller to provide the memoization implementation to accommodate process-dict based caching, node-wide caching, cluster-wide caching, or even system-wide caching via something like a db, and they could be configured to only cache when computations take a set amount, etc. Imagine the following situation: @spec get_people() :: Enumerable.t(Person.t()) @spec without_kids(people :: Enumerable.t(Person.t())) :: Enumerable.t(Personal.t()) @spec names(people :: Enumerable.t(Person.t())) :: String.t() If I implement these functions to return lists, then get_people() |> without_kids() |> names() iterates over everything 3 times. No good if I have a billion people. If I implement these functions to return streams then names = get_people() |> without_kids() |> names() first_names = Enum.map(&to_first_name/1) last_names = Enum.map(&to_last_name/1) iterates over everything twice. Okay, but I can do names = get_people() |> without_kids() |> names() |> Enum.to_list() first_names = Enum.map(&to_first_name/1) last_names = Enum.map(&to_last_name/1) This works, but it's eager. So, this names = get_people() |> without_kids() |> names() |> Enum.to_list() maybe_first_names = if :rand.uniform() > 0.5, do: Enum.map(&to_first_name/1) maybe_last_names = if :rand.uniform() > 0.5, do:Enum.map(&to_last_name/1) will still compute names even though a quarter of the time neither first_names nor last_names use names. Technically, we can already do this today by abusing the fact that we know how streams work, but of course, nobody wants people doing that. -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. To unsubscribe from this group and stop receiving emails from it, send an email to elixir-lang-core+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/68274100-c167-440e-89e3-c039ea5262f0n%40googlegroups.com.
