From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id NAA02951; Fri, 7 Feb 2003 13:54:28 +0100 (MET) X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f Received: from nez-perce.inria.fr (nez-perce.inria.fr [192.93.2.78]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id NAA02558 for ; Fri, 7 Feb 2003 13:54:27 +0100 (MET) Received: from ns.mccme.ru ([195.133.68.22]) by nez-perce.inria.fr (8.11.1/8.11.1) with ESMTP id h17CsPP01910 for ; Fri, 7 Feb 2003 13:54:26 +0100 (MET) Received: from mccme.ru (potanin@mccme.ru [195.178.198.7]) by ns.mccme.ru (8.8.5/8.8.5) with SMTP id PAA08828 for ; Fri, 7 Feb 2003 15:48:55 +0300 Date: Fri, 7 Feb 2003 16:10:23 +0300 (MSK) From: Mike Potanin To: caml-list@inria.fr Subject: [Caml-list] Re: your mail In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-caml-list@pauillac.inria.fr Precedence: bulk On Thu, 6 Feb 2003, Nikolaj Bjorner wrote: > I am pretty sure this is not related to references, but to let-rec. > > Try: > > let rec f x = x and g y = f y + 1;; > > you will see that the type inferred is: > > val f : int -> int > val g : int -> int > > Now try: > > let f x = x and g y = f y + 1;; ^ ^ This is different functions. First "f" defined new function. Second "f" referred to old function "f". > > this time: > > val f : 'a -> 'a > val g : int -> int > > You may still be wondering why, of course. > The basic answer (I hope I am not too rusty in this) > is that type inference for polymorphic let-rec is not decidable > (you have to solve a semi-unification problem). > Hence, the "solution" is not to abstract type variables > until all type inference for all > let-rec-and clauses have been analyzed. > > So: > > let rec f x = x and g y = f y + 1 and h z = not (h z);; > > does not type check at all, but again: > let f x = x and g y = f y + 1 and h z = not (h z);; > does work. > > > Nikolaj > > > > > From: Chris Hecker [mailto:checker@d6.com] > Sent: Thu 2/6/2003 5:31 PM > To: caml-list@inria.fr > Subject: [Caml-list] streams and value restriction > > > > > I assume I'm running into the polymorphism restriction thing here, but > I'm not sure why (I kind of understand it when references are in play, > but this is baffling me). > > Here's a simple version of some stream parser code. I'd like > parse_opt_comma_list to be polymorphic so I can use it to parse lists > of any of my values. It works fine as a separate let rec, but if I > put it in the overall let rec of the main parser (with and) it won't > generalize and gets tagged as string-only since that's the first way > it's used. > > Can somebody explain why this is a problem? Sorry for being dense. > > Thanks, > Chris > > > type t = > Int of int > | String of string > > (* this works: *) > let rec parse_opt_comma_list parse list = parser > [< 'Genlex.Kwd ","; > a = parse ; > optlist = parse_opt_comma_list parse (a::list) >] -> optlist > | [< >] -> list > > let rec parse_values = parser > [< 'Genlex.String s; > optlist = parse_opt_comma_list (parser [< 'Genlex.String s >] -> s) [] >] -> > (String s) :: List.map (fun s -> String s) optlist > | [< 'Genlex.Int i; > optlist = parse_opt_comma_list (parser [< 'Genlex.Int i >] -> i) [] >] -> > (Int i) :: List.map (fun i -> Int i) optlist > > (* this doesn't: *) > let rec parse_values = parser > [< 'Genlex.String s; > optlist = parse_opt_comma_list (parser [< 'Genlex.String s >] -> s) [] >] -> > (String s) :: List.map (fun s -> String s) optlist > | [< 'Genlex.Int i; > optlist = parse_opt_comma_list (parser [< 'Genlex.Int i >] -> i) [] >] -> > (Int i) :: List.map (fun i -> Int i) optlist > > and parse_opt_comma_list parse list = parser > [< 'Genlex.Kwd ","; > a = parse ; > optlist = parse_opt_comma_list parse (a::list) >] -> optlist > | [< >] -> list > > > ------------------- > To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr > Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ > Beginner's list: http://groups.yahoo.com/group/ocaml_beginners > ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners