Cleaning? Actually I'm not sure this is cleaner.

It's definitely shorter..

day5/main.exs

@@ -2,53 +2,38 @@ defmodule Day5 do
   def run do
     {rules, updates} = parseFile("data.txt")
 
-    {validUpdates, invalidUpdates} = Enum.split_with(updates, &updateValid?(&1, rules))
+    {invalidUpdates, validUpdates} = Enum.split_with(updates, &updateInvalid?(&1, rules))
 
-    validMiddles = Enum.map(validUpdates, &middleDigit/1)
-    IO.puts("Part 1: #{Enum.sum(validMiddles)}")
+    IO.puts("Part 1: #{Enum.sum(Enum.map(validUpdates, &middleDigit/1))}")
 
-    # sort the invalid ones with a custom sorter that looks for [a, b] in the rules list. if [a, b] exists, sort a before b
+    # sort the invalid ones with a sorter that looks for [a, b] in the rules list. if [a, b] exists, sort a before b
     invalidSorted =
       Enum.map(invalidUpdates, fn update ->
-        Enum.sort(update, fn first, second ->
-          Enum.member?(rules, [first, second])
-        end)
+        Enum.sort(update, &Enum.member?(rules, [&1, &2]))
       end)
 
-    invalidMiddles = Enum.map(invalidSorted, &middleDigit/1)
-    IO.puts("Part 2: #{Enum.sum(invalidMiddles)}")
+    IO.puts("Part 2: #{Enum.sum(Enum.map(invalidSorted, &middleDigit/1))}")
   end
 
   defp parseFile(file) do
-    [topSection, bottomSection] = File.read!(file) |> String.split("\n\n")
-
-    rules = String.split(topSection, "\n") |> Enum.map(fn l -> String.split(l, "|") end)
-
-    updates =
-      String.split(bottomSection, "\n")
-      |> Enum.drop(-1)
-      |> Enum.map(fn l -> String.split(l, ",") end)
-
+    # split the file by the empty line, then map splitting by newlines on both sections
+    [top, bottom] = File.read!(file) |> String.split("\n\n") |> Enum.map(&String.split(&1, "\n"))
+    rules = top |> Enum.map(&String.split(&1, "|"))
+    updates = bottom |> Enum.drop(-1) |> Enum.map(&String.split(&1, ","))
     {rules, updates}
   end
 
-  defp updateValid?(update, rules) do
-    Enum.reduce_while(rules, true, fn [left, right], acc ->
-      # if it doesn't contain both, or it does and they're in the right order
-      if !(Enum.member?(update, left) and Enum.member?(update, right)) or
-           Enum.find_index(update, &(&1 == left)) < Enum.find_index(update, &(&1 == right)) do
-        # continue and try the next one
-        {:cont, acc}
-      else
-        # otherwise halt the reduction, this update is invalid
-        {:halt, false}
-      end
+  defp updateInvalid?(update, rules) do
+    Enum.find(rules, false, fn [left, right] ->
+      # it is invalid if it contains both and they're in the wrong order
+      Enum.member?(update, left) and Enum.member?(update, right) and
+        Enum.find_index(update, &(&1 == left)) > Enum.find_index(update, &(&1 == right))
     end)
   end
 
-  defp middleDigit(update) do
-    middle = trunc(length(update) / 2)
-    String.to_integer(Enum.at(update, middle))
+  defp middleDigit(l) do
+    middle = trunc(length(l) / 2)
+    String.to_integer(Enum.at(l, middle))
   end
 end