Examples no longer work

[alexrp]

iex(1)> require Monad
nil
iex(2)> monad ErrorM do
...(2)>     a <- {:ok, 2}
...(2)>     b <- {:ok, 3}
...(2)>     return a * b
...(2)> end
** (RuntimeError) undefined function: a/0

[ibizaman]

I'm testing this with Elixir 1.1.1 and it works if I import Monad.