Hello,
I have this example where I would like a stream transformation to return the whole input list up to the third atom, included.
input = ["a", "b", "c", "d", :x, :y, "e", "f", :z, "g", "h", "i", :aa, :bb, "j"]
Expected output:
["a", "b", "c", "d", :x, :y, "e", "f", :z]
All I can do for now is to return:
["a", "b", "c", "d", :x, :y, "e", "f"]
Of course it would be very easy without the constraint: Further elements from the stream should not be processed once the final atom is found in the stream.
Do you know how I should do that?
Thank you!
Some test code:
defmodule Demo do
def run do
input = ["a", "b", "c", "d", :x, :y, "e", "f", :z, "g", "h", "i", :aa, :bb, "j"]
wanted_atoms = 3
input
#
# Classifier function. In real application it costs money to run so we never
# want to call it if we are not going to process its result.
|> Stream.map(fn
"g" -> raise ~s(should not process "g")
value when is_atom(value) -> {:atom, value}
value -> {:other, value}
end)
# Take 3 atoms if we find them in the stream, take the whole stream
# otherwise.
|> Stream.transform(
_start_fun = fn -> 0 end,
_redux_fun = fn
{:atom, value}, atom_count when atom_count == wanted_atoms - 1 -> {:halt, {:last, value}}
{:atom, value}, atom_count -> {[value], atom_count + 1}
{:other, value}, atom_count -> {[value], atom_count}
end,
__last_fun = fn
# Not called when the reducer returns :halt
{:last, value} -> {[value], nil}
n when is_integer(n) -> {:halt, nil}
end,
_after_fun = fn acc -> :ok end
)
|> Enum.to_list()
|> IO.inspect(limit: :infinity, label: "final")
end
defp get_score(2), do: {:ok, 1234}
defp get_score(_), do: {:error, :nope}
end
Demo.run()