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Comment by Yoric | Hacker News Reader

Having coded a lot in both OCaml (I used to lead OCaml Batteries Included) and Rust (I'm a contributor to the Rust compiler and stdlib), I believe that they have very different targets.

Rust is really, really good at systems-level programming, it has great concurrency, but closures are more restricted than OCaml and it doesn't have general garbage-collection.

OCaml shines to implement really complicated algorithms. Anything that requires symbolic manipulation/pattern-matching, for instance, or manipulating large graphs, or maintaining extremely complex invariants. Garbage-collection that just works is invaluable but it doesn't play nicely with multicore yet.

In other words, I believe that there's room for both in our world! I could see myself developing applications in which some components are implemented in Rust and others in OCaml.

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What's your opinion on F# ? Does it share enough of OCaml goodness to be worth using in .Net world or instead of OCaml?

F# is very much like a .NET port of OCaml. It is very nice to use and offers (usually) low effort interop with all of the worlds C# libraries.

We use it in production at Olo, and I used it in production at my last company.

Since learning F#, languages where if statements aren't expressions and that don't have option types feel broken to me =)

I can see that F# still does not support GADTs. Did you find it a serious limitation?

Depends on what you're trying to do. I've never found it to be a limitation but I don't do anything terribly intricate. Just web dev for work, and I wrote a toy language parser and type inferencer in it. There are maybe three lines of code that GADTs might have let me avoid casting in the type inferencer, but oh well. Different use cases that use GADTs to a greater extent, of course, you might miss them. What is your use case, and how much are you reliant on GADTs in your existing daily life?

You can go an entire lifetime without ever even knowing about GADTs. I don’t find their absence limiting at all.

I’ve used F# and USING it feels very similar to OCaml in all of the important ways.

The lightweight type structure where you can easily make Union types and the pattern matching are pretty much identical to how OCaml does it.

Of course, the big difference is going to be in how easily you can interop with the .Net stuff in each language, obviously much easier in F#. This is great if you happen to have some kind of weird C# code that generates an IEnumerable, just pop that into F# and start working with it.

For example, I have C# classes to read files to an IEnumerable of strings, you can just call List.ofSeq on it, and then start doing some really elegant things in F# with it. You can pattern match log files based on how the line starts and then run different functions whether it’s an error, info, debug, etc

If you are in the .NET world, then definitely prefer F# to C#. However be aware that it differs in some significant ways from OCaml. E.g., it does not have a separate module language (module types, functors, first-class modules). Its design is in a different, more object-oriented direction, with support for classes and interfaces.

Basically, if you do use F#, be aware that it has its own idioms that you must learn; it's not a drop-in replacement for e.g. OCaml/Haskell/etc.

Having used both for years, nowadays I would recommend using F#.

The syntax is very similar but it solves many of Ocaml's pain points and you will get better tooling and more libraries thanks to .Net.

Could you elaborate on the pros of F# vs OCaml?

In no particular order: - significant whitespace and no `let ... in` which makes for a more streamlined syntax - no +. vs + - a solid standard library - much improved tooling (see the ionide plugin for vscode) - you can use all the .Net libraries - multicore support - list comprehension and iterators - object support with a minimalistic syntax (I don't include type providers as I never had proper use cases for them)

All of those either remove pain points (some of them arguably very small) or introduce improvements that are sensible in day to day life.

With that and the fast that Ocaml and F# can (for the most part) easily be transpiled into one another, nowadays I see very little reason not to use F#.

That being said, I find the fact that you basically never need explicit types in Ocaml very elegant (in F# the uniform syntax mean that you will need occasional types hints to disambiguate operations).

> list comprehension

Are you referring to F#'s computation expressions? If so, OCaml has a similar-in-power let-syntax now: http://jobjo.github.io/2019/04/24/ocaml-has-some-new-shiny-s...

> Ocaml and F# can (for the most part) easily be transpiled into one another,

Actually they can't. They are quite different languages in practice.

No, I am referring to proper list comprehensions (as you would get in python): https://en.wikibooks.org/wiki/F_Sharp_Programming/Lists#Usin...

Its true that you can't literaly transpile very high order things such as GADT but the was majority of code is trivial to translate as both syntax and available constructs match.

I practice, I found translations between the two languages to be fairly easy (the same cannot be said for most language pairs).

(I was not aware of the new let-syntax, thats a nice addition (although computation expression did not make my list as they are more of an enabler for library authors than normal users). I will dig in to see what people build around it...)

> I am referring to proper list comprehensions

Oh cool, I'd forgotten F# had those (or maybe it got them recently?).

> Its true that you can't literaly transpile very high order things such as GADT but the was majority of code is trivial to translate

Would still have to disagree there; OCaml code heavily relies on modules/module types/functors, while F# code relies more on classes. In practice these are not trivially translateable.

> I will dig in to see what people build around it...

The major thing is getting an async/await-like syntax for concurrent operations. Super useful for literally everyone. E.g. my project https://github.com/yawaramin/re-web/blob/eb7ce8474d34c60f9f9...

How do you transpile f# to ocaml? Does this mean you can get a native self contained binary out of f# code, by first converting it to ocaml code?

I was mentionning manually translating a code base from one language to the other. I am not aware of a tool to do that (which, as others have said, would be tricky to do automatically for some constructs).

You can't. See https://news.ycombinator.com/item?id=22394667

I never seriously used F#, so I can't tell for sure, but it looks pretty good!

Besides GC and the lightweight syntax (relative to Rust), what is it about OCaml that makes it so wonderful for implementing complicated algorithms?

Well, the big one is GC.

Here are a few others:

- both polymorphic variants and GADTs are extremely powerful mechanisms to let you keep track of invariants, in a manner that cannot be replicated readably in Rust so far;

- OCaml's pattern-matching is a bit more flexible than Rust's ;

- (thanks to the GC) OCaml's closures are much more flexible than Rust closures;

- I guess OCaml's blindingly fast exceptions can be useful for some algorithms, although I haven't really experienced the need for them myself.

Again, that's not to say that Rust doesn't have great stuff for it (affine types 4eva!) or that OCaml doesn't have its own limitations – Rust is currently my main language and I do not regret it.

But there are some algorithms that I really don't want to write in Rust. Recently, for instance, I stumbled upon this: http://weblog.jamisbuck.org/2010/12/29/maze-generation-eller... . Trivial algorithm, trivial to write in OCaml, feasible but much less straightforward in Rust.

Exactly that, lock-free algorithms are specially hard to get a correct implementation without tracing GC support.

Why?

Here is an overview, read also the comments.

https://concurrencyfreaks.blogspot.com/2017/08/why-is-memory...

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