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

[Nicolas C. <war...@fr...>]

> > > Hello,
> > >
> > > Some useful operations over the keys of a map are not provided by the
> > > standard Map module, neither by ExtLib's PMap, but are provided only
by
> > > the Set module.
> >
> > Yes I would also love to set  diff / union / intersection for PMaps.
> > But I'm not sure which semantic is appropriate.
> > Maybe only have diff / union / inter operations on *keys* would be
enough ?
> > Please fell free to post implementation, maybe based on Set module.
>
> What do you think of this:
>
> (* default merge = fun x y -> x *)
> val union : ?merge:('b -> 'b -> 'b) -> ('a, 'b) t -> ('a, 'b) t -> ('a,
'b) t
>
> (* a merge function must be given to inter *)
> val inter : merge:('b -> 'c -> 'd) -> ('a, 'b) t -> ('a, 'c) t -> ('a, 'd)
t
>
> val diff : ('a, 'b) t -> ('a, 'c) t -> ('a, 'b) t

Why not generalize a little more ?

val union : merge:('b -> 'c -> 'd) -> ('a,'b) t -> ('a,'c) t -> ('a,'d) t

The only problem is that we can't use "identity" as default merger.

Nicolas