EDIT: This is wrong I initially thought the same thing, due to the use of `map` as something of an equivalent of the Haskell `bind` (>>=) operator. It reminded

EDIT: This is wrong I initially thought the same thing, due to the use of `map` as something of an equivalent of the Haskell `bind` (>>=) operator. It reminded me of just using `fmap`. But no, they are using it as a full monad. Consider the type of fmap: Functor f => (a -> b) -> f a -> f b and the type of (>>=) Monad m => m a -> (a -> m b) -> m b The key difference is the function argument. In a Functor, the argument is (a -> b), but in a Monad, it's (a -> m b). The distinction is that when you `fmap` a function over a `Just` value (`Some` in Rust), you always get back a `Just` value, but when you bind a `Maybe` value into a function, you might get back a `Nothing`. So don't let Rust's use of `map` deceive you -- it seems to be the same as (>>=). That being said, I'd be interested to see Rust introduce something akin to do-notation syntactic sugar. ======= EDIT: I am wrong, the `map` function is basically equivalent to `fmap` and it seems the `and_then` function is similar to (>>=). See user tel and user wyager's responses.