From: Chris Hecker <checker@d6.com>
To: caml-list@inria.fr
Subject: [Caml-list] streams and value restriction
Date: Thu, 6 Feb 2003 17:31:24 -0800 [thread overview]
Message-ID: <200302070131.h171VJu24020@plinky.bolt-action.com> (raw)
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
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next reply other threads:[~2003-02-07 0:22 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-02-07 1:31 Chris Hecker [this message]
2003-02-07 7:36 ` Jacques Garrigue
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