Unexpected interaction between `Stream.concat`, `Stream.take`, and `Stream.transform`

[4xrsJCr9]

% iex
Erlang/OTP 19 [erts-8.2] [source-fbd2db2] [64-bit] [smp:2:2] [async-threads:10] [hipe] [kernel-poll:false]

Interactive Elixir (1.4.0) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> [1] |> Stream.concat([2]) |> Stream.take(1) |> Stream.transform(0, fn e, a -> {[e], a} end) |> Enum.to_list
[1]
iex(2)> [1] |> Stream.take(1) |> Stream.concat([2]) |> Stream.transform(0, fn e, a -> {[e], a} end) |> Enum.to_list
** (TryClauseError) no try clause matching: {:suspended, [2, 1], #Function<20.36862645/1 in Stream.do_list_transform/9>}
    (elixir) lib/stream.ex:784: Stream.do_transform/8
    (elixir) lib/enum.ex:1776: Enum.reverse/2
    (elixir) lib/enum.ex:2528: Enum.to_list/1
iex(2)>

Environment

Elixir 1.4.0
Linux 3.13.0-85-generic #129-Ubuntu SMP x86_64 GNU/Linux

Current behavior

The second expression (iex(2)) raises an error.

Expected behavior

The result of the second expression (iex(2)) should be the same as that of the first expression (iex(1)) [1, 2].

[kelvinst]

First of all, I guess the result will not be the same, that's a wrong assumption since if you concat first and take one after you would have [1] and if you take one first and concat after you would get a [1, 2].

Anyways, I'm investigating why this is happening, I guess it's really a bug. Thank you for the report!

[4xrsJCr9]

First of all, I guess the result will not be the same, that's a wrong assumption since if you concat first and take one after you would have [1] and if you take one first and concat after you would get a [1, 2].

Sorry about that; it just slipped my mind.

[4xrsJCr9]

Would I be correct in stating that this is caused when the case where curr is 1 returns a {:halt, _} rather than {:suspend, _}, as the indirect caller of the function (generated by the take macro from the reducers module) expects?

fn(entry, acc(head, curr, tail) = original) ->
        case curr do
          0 ->
            {:halt, original}
          1 ->
            {_, acc} = next_with_acc(unquote(fun), entry, head, 0, tail)
            {:halt, acc}
          _ ->
            next_with_acc(unquote(fun), entry, head, curr - 1, tail)
        end
end