Simple/Naive Implementation of Identity and Maybe Monad in Elixir
I think you're sort of missing the point with this code - the difference between different kinds of monads (Maybe vs. List vs. Identity, etc.) is in the different implementations of return and bind. I think a good starting place might be reading through a library that implements monads in elixir, like monad. Looking into that you can see that for example Maybe is implemented like this (simplifying):

def return(x), do: {:just, x}

def bind({:just, x}, f), do: f.(x)
def bind(:nothing, _), do: :nothing

def fail(_), do: :nothing


While  for example Error (the second-simplest I think) is implemented like this:

def return(x), do: {:ok, x}

def bind(e = {:error, _}, _), do: e
def bind({:ok, x}, f), do: f.(x)

def fail(msg), do: {:error, msg}


The difference between the two being that in one case you only get information that there is no result (:nothing) while in the other you either get a result or some information on the error (represented by {:error, _}). Also note that both have additional helper functions to for example extract the result (presumably at the end of the computation).