How are the “labled” modules of the standard library implemented? If I follow the definition of, let’s say, ListLabels.map, vscode points me to the implementation of List.map, ArrayLabels.map points to Array.map and so on. If we look at the ListLabels module implementation on Github , we can see th…

I use StdLabels a lot, personally. Edit: they are also used in the js_of_ocaml codebase.

Yes, they are used in some projects (notably Dune and JSOO), but I don’t have any hard numbers about how much they are used in the large, besides some anecdotical evidence. This can probably be obtained by grepping over the OPAM sources and could be useful information to have to inform the upstream …

[image] nojb: The implementation of labeled modules (which are, as you noticed, unlabeled) are compiled with -nolabels which tells the typechecker to ignore labels altogether. In particular this makes the (unlabeled) implementations compatible with the (labeled) interfaces. The -nolabels flag i…

[image] benjamin-thomas: I’d be interested to hear how one could make this work with a dune workflow. I think it will be hard to do because as far as I know it is not possible to have Dune pass a separate set of flags when compiling the interface and the implementation of a given module. Che…

Sherlocode shows they’re not used that much, see ListLabels and ArrayLabels . I wish they were simply removed from the stdlib…

Thanks for the feedback Nicolas. – IMO, labeling a parameter when it there is no ambiguity, like f in map, is not very useful. But it’s pretty nice to have labeled arguments when several arguments have the same type. # Array.sub;; - : 'a array -> int -> int -> 'a array = <fun> # ArrayLabels.sub;…

[image] benjamin-thomas: IMO, labeling a parameter when it there is no ambiguity, like f in map, is not very useful. Actually it is, because it allows you to supply the parameters in either order, which is very useful for pipin g with |> and also means you don’t have to remember the order.

What I meant is that map already has its arguments in an order which is pipe-friendly (unlike some other functions I bump into every now and then). There is no ambiguity and it seems to me that the labeled version is verbose for no obvious benefit. # [1;2;3] |> List.map (( * ) 2);; - : int list = …

Not so relevant for maps, but for folds note that using a signature such as: val fold : 'val t -> 'acc -> f:(key -> 'val -> 'acc -> 'acc) -> 'acc yields stronger type-based disambiguation power for the the definition of f if it is written as a lambda, as compared to: val fold : (key -> 'val -> 'a…

How are ListLabels, ArrayLabels, etc. implemented?

Learning

dbuenzli November 4, 2023, 2:59pm 10

I once tried to suggest this but I gave up. I still think they mostly add more noise to the system but they seem cherished by enough people so that this is unlikely to happen.

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How are ListLabels, ArrayLabels, etc. implemented?

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