‘a. means “for all types ‘a”. The OCaml top-level usually doesn’t bother showing it, which is why it doesn’t appear in the output. Any expression printed that contains type variables has an implicit forall at the start unless shown elsewhere. When defining a function, it can be useful to add this at the start to … Read more
This is sometimes called a “record update” or “functional update” or something like that. It evaluates to a new record of the same type as X, and whose fields are initialized to the same as those in X, except the ones which are listed after the “with”, which are initialized to those given values. It … Read more
There is no idiom that I know of, but here is a fairly natural definition using an infix operator: # let (–) i j = let rec aux n acc = if n < i then acc else aux (n-1) (n :: acc) in aux j [] ;; val ( — ) : int -> … Read more
“What are the benefits of OCaml as a programming language” is indeed an opinion-based question, and one that I’m not going to tackle here. However, I work on the Hack team at Facebook, and have worked closely with the Flow team, so I can answer the question I think you intended to ask: “Why did … Read more
Compile with -g and set environment variable OCAMLRUNPARAM=b
Caveat: I’m one of the authors of Batteries (although I’ve been out of touch for a year now) and the author of the about page linked above. The big differences are the following: Core is used daily in an industrial environment, while afaik Batteries doesn’t have the same following Core is maintained by one company, … Read more
The answer here is the same as for flip :-). Function composition isn’t defined in the OCaml standard library. In this case, it isn’t something I miss once in a while, I miss it all the time. The OCaml Batteries Included project defines function composition (in the order you give) using the operator -| in … Read more
This 2009 issue of the Caml weekly news (“CWN”, a digest of interesting messages from the caml list) shows that: the official party line on threads and Ocaml hasn’t changed. A notable quote: (…) in general, the whole standard library is not thread-safe. Probably that should be stated in the documentation for the threads library, … Read more
You should become familiar with the List.iter and List.map functions. They are essential for programming in OCaml. If you also get comfortable with the Printf module, you can then write: open Printf let a = [1;2;3;4;5] let () = List.iter (printf “%d “) a I open Printf in most of my code because I use … Read more
There are some differences feature-wise, as well as semantically. Features SML supports but not OCaml: transparent signature ascription module-level let symmetric sharing constraints syntactic sugar for functors over types and values Features OCaml 4 has but not SML: higher-order functors recursive modules local modules nested signatures modules as first-class values general module sharing (sig with … Read more