The nuances of OOP in F# can be ignored by beginners, so I really wouldn’t let yourself be intimidated coming from Clojure.
I don’t know much about F#, but last time I used it most of its standard library was in C# and .NET, so F# code would interact with objects and classes a lot. AFAIK F# also doesn’t have functor modules, so even without the dependence on C# code, you still can’t avoid classes and objects like you can with OCaml (e.g. you can’t write a generic collection module like `List` or `Set` without functors, it would have to be a collection of a specific type or a class).
It's not a yes/no feature.
https://learn.microsoft.com/en-us/dotnet/fsharp/language-ref...
FTFM: It's not a true/false feature.
Is "emphasizes" just another word for second-class support?
C++ emphasizes the importance of memory safety.
https://www.infoworld.com/article/3714401/c-plus-plus-creato...
Haskell enforces this via a type system.
What safeguards around mutability does Clojure have?
If I import a method 'foo()', is there any kind of contract, notation ... anything which could suggest whether it mutates or not?
Very nearly the entire language and standard library operate on immutable values only. Immutable values are the default, and you will use them for the vast majority of logic. You must do so, unless you very specifically opt to use dedicated reference types, at which point you’ll still need to produce intermediate immutable values to interact with that vast majority of the standard library.
And…
> is there any kind of contract, notation ... anything which could suggest whether it mutates or not?
Functions which mutate state are almost always suffixed !. They will typically fail if you pass them immutable values; they only operate on reference types, which have to be dereferenced (typically with the prefix @) to access their state.
I don't know what's your personal definition of "second-class support" but what it means is that it's explicitly supported by the language.
What safeguards does the language actually put in-place?
I don't think you know what you're talking about. Managing object ownership through systems like smart pointers is not memory safety. Applications that use smart pointers still suffer from memory issues, and it's possible to adopt object ownership systems that still use raw pointers, such as It's object ownership system.
Right. I sound just like someone talking about how "a language which emphasizes immutability" is an OK replacement for a language with pure functions.
Functions in Haskell including Prelude can throw exceptions which is not reflected in the type signature of the function. That is an effect that makes seemingly pure functions impure.
You can’t judge a language from a list of buzzwords. You need to look at how it is used in practice.
No, bottom, or _|_, is an inhabitant of every lifted type. An exception is bottom. So the / function is still pure even though it can throw a divide-by-zero exception.
Also interesting that when FP is mentioned, Hindley-Milner is implicitly understood to be part of FP too even though it doesn’t have to be. Clojure emphasizes immutability and FP but with dynamic typing and everything that comes with that.