Re: [Ocaml-lib-devel] Map with set operations over the keys

[Alain F. <Ala...@in...>]

If you want to provide a generic point-wise binary combinator for maps,
the type should be something like:

(key -> 'a option -> 'b option -> 'c option) ->
   'a t -> 'b t -> 'c t

The first argument is never called with two None arguments, and
you might prefer to use exception to signal elements to remove, instead
of a None result, so another type could be:

(key -> 'a -> 'c) -> (key -> 'a -> 'b -> 'c) -> (key -> 'b -> 'c) ->
  'a -> 'b t -> 'c t


In my experience, having such a generic point-wise combinator on
map-like structures is really useful. Maybe you also want special cases
(as a convenience for the user but also to optimize the implementation),
but I really believe a generic version should be offered in the interface.

-- Alain