You make these broad statements about monads as if FP was the whole programming world. It's not. It's probably less than 5% of it.
Nope.
> State is encapsulated in an object and transformed by method calls.
Monads aren't objects (which necessarily have a runtime manifestation). Monads (as used in functional programming) are abstract type constructors (which normally don't have a runtime manifestation).
> Method calls can be chained, and state can be encapsulated and extracted using constructors and accessors, respectively.
Monadic bind satisfies three concrete, clearly defined algebraic laws. The use of monads in functional programming arose from the field of denotational semantics, which gives “programs” (by which functional language semanticists mean “expressions”) precise mathematical meanings in a compositional manner.
I didn't say Monads were objects. I simply talked through the most common properties and operations of OOP code, in order to show how they are closely related to the operations on Monads.
I understand that OOP code does not, in general, satisfy the constraints of Monads. Hence, why I specified high-quality OOP code, which, in contrast, typically does.
Last I checked, there are only three laws: left/right identity and associativity, and they are just algebraic laws that have nothing to do with your code being “good” or “bad”. Or do you have some other meaning of “rules of monads” in mind?
Furthermore, every higher-order strict language is already monadic, without you having to do anything special. Thus, monads aren't opt-in, or even opt-out; they're there whether you like it or not. This monadic structure permeates the language, regardless of whether you write “good” or “bad” programs in it. For more info, see here: https://news.ycombinator.com/item?id=13823145
Yes, all higher-order strict languages can be embedded in a monadic model. However, there's an important practical difference between a single Monad with the entire application or computer's state encapsulated (course grain encapsulation), and many Monads with fine-grained encapsulation. High-quality OOP code can be embedded in the latter, and that's where the maintainability comes from.
--- Perhaps, if you focused more on understanding the point I'm trying to make instead of proving me wrong, this conversation would be more beneficial to both of us.
And, by "intrinsic", do you mean that "the language does that, but the programmer doesn't have to do anything to make it happen, or even know"? If so, doesn't this contradict your answer to smaddox?
If so, I don't know why the "higher-order" restriction is there. It seems unneeded. Also, it about is as much something "the programmer doesn't have to do anything or even know" as monadic code on languages that have specialized syntactic sugar, like Haskell. It creates plenty of details the programmer has to think about, the only difference is that in procedural languages all the details are always there, while in pure ones the detail set changes all the time.
Procedures as first-class values that you can store in variables, pass as arguments to other procedures, etc.
> And, by "intrinsic", do you mean that "the language does that, but the programmer doesn't have to do anything to make it happen, or even know"?
Yes. Although, IMO, programmers benefit from knowing it, for more or less the same reasons civil engineers benefit from knowing the laws of nature.
> If so, doesn't this contradict your answer to smaddox?
No. Monads, as abstract type constructors, are already hardcoded into the result type of every computation. (This is the difference between, say, an int like “2”, and a computation that produces an int like “1 + 1” or “fix (\x -> x + 1)”.) So hardcoded, in fact, that there doesn't have to be syntax for it, because there's no way you can not say it.