chop.erl

-module(chop).

-export([guess/3]).

-define(equal(Actual, Guess), Guess == Actual).

-define(lower(Actual, Guess), Guess > Actual).

guess(Actual, First, Last) ->
  Guess = binary_guess(First, Last),
  higher_lower(Actual, First, Last, Guess).

higher_lower(Actual, _, _, Guess) when ?equal(Actual, Guess) ->
  io:fwrite(io_lib:format("~p~n", [Guess]));

higher_lower(Actual, First, _, Guess) when ?lower(Actual, Guess) ->
  io:fwrite("Is it ~p~n", io_lib:format("~p", [Guess])),
  guess(Actual, First, Guess);

higher_lower(Actual, _, Last, Guess) ->
  io:fwrite("Is it ~p~n", io_lib:format("~p", [Guess])),
  guess(Actual, Guess, Last).

binary_guess(First, Last) -> First + ((Last - First) / 2).

chop.exs

defmodule Chop do
  defmacro is_equal(actual, guess) do
    quote do
      unquote(guess) == unquote(actual)
    end
  end

  defmacro is_lower(actual, guess) do
    quote do
      unquote(guess) > unquote(actual)
    end
  end

  def guess(actual, first .. last) do
    guess = guestimate(first, last)
    higherlower(actual, (first..last), guess)
  end

  def higherlower(actual, _ .. _, guestimate) when is_equal(actual, guestimate) do
    IO.puts guestimate
  end

  def higherlower(actual, first .. last, guestimate) when is_lower(actual, guestimate) do
    IO.puts "Is it #{guestimate(first, last)}"
    guess(actual, (first..guestimate))
  end

  def higherlower(actual, first .. last, guestimate) do
    IO.puts "Is it #{guestimate(first, last)}"
    guess(actual, (guestimate..last))
  end

  def guestimate(first, last) do
    first + div((last - first), 2)
  end
end