Take a look at https://github.com/Schultzer/unidekode/blob/master/lib/unidekode.ex I do something similar.

I am very late here but kept this thread open since this interested me.

This is what I came up with (~4.82 μs per function call with the parameter "01xyz234abc567def890!"):

defmodule Translit do
  def western_to_eastern(string, acc \\ "")

  def western_to_eastern(<<>>, acc), do: acc

  ~c[0123456789]
  |> Enum.zip(~c[٠١٢٣٤٥٦٧٨٩])
  |> Enum.each(fn {western, eastern} ->
    def western_to_eastern(<<unquote(western)::utf8, rest::binary>>, acc), do: western_to_eastern(rest, acc <> unquote(to_string([eastern])))
  end)

  def western_to_eastern(<<any::utf8, rest::binary>>, acc), do: western_to_eastern(rest, acc <> to_string([any]))
end

Why does unquote work without a quote block though, I have no idea.

def’s are implicit quote blocks is why.