Nothing in MaybeT monad: more concise way?

Question

I'm experimenting with the MaybeT monad, specifically MaybeT Identity String

import Control.Monad.Trans.Maybe
import Control.Monad.Identity
import Data.Maybe

main :: IO ()
main = putStrLn . show . runIdentity . runMaybeT $ maybeGetString

maybeGetString :: MaybeT Identity String
maybeGetString = return "first" >>
                 maybeTNothing >> 
                 return "second"

maybeTNothing :: MaybeT Identity String
maybeTNothing = MaybeT $ return Nothing

The experession for the MaybeT equivalent of Nothing seems to be MaybeT $ return Nothing, which feels a bit verbose, and it feels unexpected to me to have to explicitly use the MaybeT constructor.

Is there a shorter/nicer/clearer way of writing Nothing in the MaybeT monad?

Answer 1

Inspired by the comment from @luqui

---

To behave as Nothing in the plain Maybe monad, maybeTNothing should satisfy the equations

maybeTNothing >>= f  =  maybeTNothing
v >> maybeTNothing   =  maybeTNothing

This is exactly the requirements on mzero from MonadPlus, which MaybeT is an instance of. So we can just use mzero

maybeTNothing = mzero

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https://hackage.haskell.org/package/base-4.9.1.0/docs/Control-Monad.html#t:MonadPlus