Stream.chunk_while/4

defmodule Stream do
  def chunk_while(stream, acc, fun, after_fun)
end

Chunks stream with fine grained control when every chunk is emitted.

fun receives the current element and the accumulator and must return

• {:cont, chunk, acc} to emit the given chunk and continue with accumulator or
• {:cont, acc} to not emit any chunk and continue with the return accumulator.

after_fun is invoked when iteration is done and must also return {:cont, chunk, acc} or {:cont, acc}.

The iteration stops as soon as fun returns a tuple of the form {:halt, acc}.