Add several elixir solutions

elixir/grains/lib/grains.ex

@@ -0,0 +1,23 @@
+defmodule Grains do
+  @doc """
+  Calculate two to the power of the input minus one.
+  """
+  @spec square(pos_integer()) :: {:ok, pos_integer()} | {:error, String.t()}
+  def square(number) when number < 1 or number > 64 do
+    {:error, "The requested square must be between 1 and 64 (inclusive)"}
+  end
+  def square(number), do: {:ok, 2**(number-1)}
+
+  @doc """
+  Adds square of each number from 1 to 64.
+  """
+  @spec total :: {:ok, pos_integer()}
+  def total do
+    Enum.reduce_while(1..64, {:ok, 0}, fn n, {:ok, sum} ->
+      case square(n) do
+        {:ok, squared} -> {:cont, {:ok, squared + sum}}
+        {:error, error} -> {:halt, {:error, error}}
+      end
+    end)
+  end
+end