# Simplified representation of source data
data = ["A", "B", "B", "A", "C", "A", "D"]
Stream.transform(data, "", fn(line, acc) ->
  if line == "A" do
    if acc == "", do: {[], line}, else: {[acc], line}
  else
    {[], acc <> line}
  end
end) |> Enum.to_list
# Desired: ["ABB", "AC", "AD"]
# Result: ["ABB", "AC"]