Like others, using Range

...
|> Enum.map(& &1 |> String.replace("-", "..") |> Code.eval_string() |> elem(0))

and then

|> Enum.map(fn [r1, r2] -> not Range.disjoint?(r1, r2) end)

My simple solution:

defmodule Day04 do
  def part1(input_path) do
    input_path
    |> File.stream!()
    |> Stream.map(&String.trim/1)
    |> Stream.map(&String.split(&1, ~r/\D/, global: true))
    |> Stream.map(fn x -> Enum.map(x, &String.to_integer/1) end)
    |> Enum.count(fn [start1, end1, start2, end2] ->
      (start1 <= start2 and end1 >= end2) or
      (start1 >= start2 and end1 <= end2)
    end)
  end

  def part2(input_path) do
    input_path
    |> File.stream!()
    |> Stream.map(&String.trim/1)
    |> Stream.map(&String.split(&1, ~r/\D/, global: true))
    |> Stream.map(fn x -> Enum.map(x, &String.to_integer/1) end)
    |> Enum.count(fn [start1, end1, start2, end2] ->
      start1 <= end2 and start2 <= end1
    end)
  end
end

Advent of code always reminds me what a great “stdlib” Elixir comes with!

  parsed = 
    input
    |> String.split("\n", trim: true)
    |> Enum.flat_map(&String.split(&1, ~r/[-,]/))
    |> Enum.map(&String.to_integer/1)
    |> Enum.chunk_every(4)

part1 = Enum.count(parsed, fn [ax, ay, bx, by] -> (ax <= bx and ay >= by) or (ax >= bx and ay <= by) end)
part2 = Enum.count(parsed, fn [ax, ay, bx, by] -> (bx <= ay and by >= ax) end)

Edit: @Aetherus you beat me by a few seconds

day04.exs:

solve = fn oper ->
  "data/04"
  |> File.read!()
  |> String.split(["\n", ",", "-"], trim: true)
  |> Enum.map(&String.to_integer/1)
  |> Enum.chunk_every(4)
  |> Enum.filter(fn [a, b, c, d] -> oper.(c in a..b, d in a..b) or oper.(a in c..d, b in c..d) end)
  |> Enum.count()
end

(&and/2)
|> then(solve)
|> tap(&IO.puts("Part 1: #{&1}"))

(&or/2)
|> then(solve)
|> tap(&IO.puts("Part 2: #{&1}"))