if the stream is "aaaafoo" and the word to search for is "foo", the function should print "Found foo" on the 6th incoming char (the last 'o' in "foo").

foo.ex

defmodule Foo do
  def find(word) do
    find(IO.getn(""), word, word)
  end

  def find(_char, "", word) do
    IO.puts "Found #{word}"
  end

  def find(char, << char :: binary-size(1), rest :: binary >>, word) do
    find(IO.getn(""), rest, word)
  end

  def find(_char, part, word) do
    find(IO.getn(""), part, word)
  end
end
Foo.find("foo")