IMO one of the best monads for explaining the concept is async promises, especially for JS programmers who haven't always had the luxury of async/await. If we

IMO one of the best monads for explaining the concept is async promises, especially for JS programmers who haven't always had the luxury of async/await. If we have a long-running process, we can block the thread and wait for it to return us a result, but that's far from ideal. Instead we return a "promise", a structure that we can provide with a callback (using the `then` method on the promise) to manipulate the result of our asynchronous processing. The types look something like this: `doSomeAsync(T1): Promise<T2>` `Promise<T2>.then(T2 -> T3): Promise<T3>` Let's look at the type of monad `bind`, `>>=` in Haskell: `M a -> (a -> M b) -> M b` The types of `bind` and `then` are very similar! `Promise` is (approximately) a monad. The fact that we can't just "get" the result of the Promise and instead need to provide a callback is a core part of my understanding of the use of monads in Haskell -- they are used in Haskell to represent the result of a non-deterministic effect. You can't (or shouldn't) just get the value out of a monad, in the same way that you can't just get "the" value out of an array -- it doesn't make much sense to talk about. The use of monads to represent non-deterministic effects is a software engineering choice. The "monad" itself is just the structure of computation where you have a wrapped thing `M a`, to which you apply a "callback" `a -> M b`, to receive a monadic result `M b`. There are also some laws which a well-behaved monad needs to follow. The point of this is that even though that `b` might never eventuate, or might come about later, or might be multiple values, the `M b` can be treated as a plain-old function result and the type checker is able to make stronger guarantees. Pretty handy when your language is based around pure functions. Side note: async/await is pretty much do-notation for Promises. You write imperative-looking code and it gets magically turned into asynchronous callbacks for you.