Elixir Snippets

main.exs

# binary pattern matching, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

defmodule Main do
  def str_str(haystack, needle) do
    match(haystack, needle, 0)
  end

  def match(<<s, str::binary>>, <<s, needle::binary>>, index) do
    needle_len = needle |> String.length()

    if str |> String.slice(0, needle_len) == needle do
      index
    else
      match(str, <<s>> <> needle, index + 1)
    end
  end

  def match(<<s, str::binary>>, <<c, needle::binary>>, index) do
    match(str, <<c>> <> needle, index + 1)
  end

  def match(_, _, _) do
    -1
  end
end

Main.str_str("Parapsychology", "psychology") |> IO.inspect()