[masklinn]

Surely since you have monads you can just use the tools they give you?

    fn = liftM2 (+)

[zenhack]

That doesn't do quite the same thing; the original example gets rid of the Maybe, defaulting to 0.

[masklinn]

> That doesn't do quite the same thing

You're missing the point entirely.

> the original example gets rid of the Maybe, defaulting to 0.

http://hackage.haskell.org/package/base-4.10.1.0/docs/Data-M...