Day 13

lib/common.ex

@@ -37,7 +37,9 @@ defmodule Aoc2023.Common do
   def lines(x), do: String.split(x, "\n")
 
   def head([head | _]), do: head
+  def head([]), do: nil
   def tail([_ | tail]), do: tail
+  def tail([]), do: nil
 
   def lcm(a, b), do: div(abs(a*b), Integer.gcd(a,b))
   def lcm(ls), do: ls |> Enum.reduce(&lcm/2)
@@ -55,6 +57,6 @@ defmodule Aoc2023.Common do
     |> Stream.map(pipe(elem(0)))
   end
 
-  def repeat(lst, 0), do: []
+  def repeat(_, 0), do: []
   def repeat(lst, n), do: Enum.concat(lst, repeat(lst, n - 1))
 end