clean up runner

lib/aoc_runner.ex

@@ -1,28 +1,36 @@
 defmodule AOCRunner do
-  defp is_empty(s) do
-    (s |> String.trim() |> String.length()) == 0
+  @spec is_empty?(s :: String.t()) :: boolean()
+  defp is_empty?(s) do
+     String.trim(s) |> String.length() == 0
   end
 
+  @spec both_empty?(a :: String.t(), b :: String.t()) :: boolean()
+  defp both_empty?(a, b) do
+    is_empty?(a) && is_empty?(b)
+  end
+
+  @spec run(advent :: Advent, part :: :part1 | :part2) :: nil
   def run(advent, part) do
-    {_, state} = IO.stream() |>
+
+    # runs the advent execute method with the current line,
+    # until two empty lines are sent
+    run_until_exit = fn line, acc -> 
+      {_, state} = acc
+
+      put_elem(acc, 1, advent.execute(line, state)) |>
+      then(fn {last_line, s} ->
+        {(if both_empty?(line, last_line), do: :halt, else: :cont), {String.trim(line), s}}
+      end)
+    end
+
+    IO.stream() |>
       Enum.reduce_while(
         {nil, advent.init_state(part)},
-      fn line, acc -> line
-        |> then(fn line ->
-            {u, state} = acc
-            {u, advent.execute(line, state)}
-          end)
-        |> then(fn {u, s} ->
-            if (line |> is_empty()) && (u |> is_empty()) do
-              {:halt, {u, s}}
-            else
-              {:cont, {u, s}}
-            end
-          end)
-        |> then(fn {reduce_atom, {_, state}} -> {reduce_atom, {String.trim(line), state}} end)
-      end
-    )
+        &run_until_exit.(&1, &2)) |>
+      elem(1) |>
+      advent.get_answer() |>
+      IO.puts()
 
-    IO.puts(advent.get_answer(state))
+    nil
   end
 end