From: bob zhang <bobzhang1988@gmail.com>
To: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
Cc: Caml List <caml-list@inria.fr>
Subject: [Caml-list] A problem about polymorphism variant
Date: Sat, 20 Oct 2012 21:59:10 -0400 [thread overview]
Message-ID: <CANcqPu7yAw6My8htudU11Xc+T7z==+rfVfYrSmQuBfJfHnGeoQ@mail.gmail.com> (raw)
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Dear Jacques:
I was reading the manual of chap4, it says
*tag-spec-full*::=`*tag-name<http://www.askra.de/software/ocaml-doc/4.00/manual011.html#tag-name>
* [ of *typexpr<http://www.askra.de/software/ocaml-doc/4.00/types.html#typexpr>
* ] { & *typexpr<http://www.askra.de/software/ocaml-doc/4.00/types.html#typexpr>
* } ∣ *typexpr<http://www.askra.de/software/ocaml-doc/4.00/types.html#typexpr>
*
I don't follow the (&) operation here, it means intersection types ?
I managed to make a working example:
type 'a ab = [< `a|`b] as 'a ;;
type 'a ac = 'a constraint 'a = [< `a | `c ]
type ('a,'b) m = [< `m of 'a ab & 'a ac ] as 'b;;
let u : ('a,'b) m = `m `a;;
(* val u : ([ `a ], [ `m of [ `a ] ab ]) m = `m `a *)
But still don't understand its use case, can you explain a bit about
this?
Many thanks
--
Regards
-- Bob
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