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 SAA02725; Mon, 29 Sep 2003 18:42:49 +0200 (MET DST)
X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id SAA08977 for <caml-list@pauillac.inria.fr>; Mon, 29 Sep 2003 18:42:47 +0200 (MET DST)
Received: from pauillac.inria.fr (pauillac.inria.fr [128.93.11.35])
	by concorde.inria.fr (8.11.1/8.11.1) with ESMTP id h8TGgAH12708;
	Mon, 29 Sep 2003 18:42:10 +0200 (MET DST)
Received: (from weis@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id SAA08681; Mon, 29 Sep 2003 18:42:09 +0200 (MET DST)
From: Pierre Weis <pierre.weis@inria.fr>
Message-Id: <200309291642.SAA08681@pauillac.inria.fr>
Subject: Re: [Caml-list] Printf question
In-Reply-To: <20030927091408.GB14604@redhat.com> from Richard Jones at "Sep 27, 103 10:14:08 am"
To: rich@annexia.org (Richard Jones)
Date: Mon, 29 Sep 2003 18:42:09 +0200 (MET DST)
Cc: caml-list@inria.fr
X-Mailer: ELM [version 2.4ME+ PL28 (25)]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-Loop: caml-list@inria.fr
X-Spam: no; 0.00; pierre:01 weis:01 pierre:01 weis:01 caml-list:01 printf:01 sth:99 dbh:99 salary:01 emp:99 sth:99 type-safety:01 compile-time:01 dbh:99 salary:01 
Sender: owner-caml-list@pauillac.inria.fr
Precedence: bulk

[...]
> This is right. I didn't make my original point clear.
> 
> I'd like to write something like:
> 
> let sth = dbh#prepare "select salary from emp where id = %d and name = %s" in
> let res = sth#execute 1 "Jones" in
> (* ... *)
> 
> The type-safety issue is that the arguments to the #execute method be
> checked at compile-time.
> 
> Using %a I need to write something like:
> 
> let sth = dbh#prepare "select salary from emp where id = %a and name = %a" in
> let res = sth#execute int_conversion 1 str_conversion "Jones" in
> 
> which is fine but the compiler doesn't check that the id passed is
> really an int. I might as well have written:
> 
> let sth = dbh#prepare "select salary from emp where id = ? and name = ?" in
> let res = sth#execute [ `Int 1; `String "Jones" ] in
> 
> and just defer the checking to runtime (in fact, defer it to the
> database in this case).

[...]

I'm pretty sure that format string contsnats are typechecked
statically with the usual typechecker resolution mechanism (a bit more
complex, but no more magic than the typechecking of the -> type
constructor).

So why not using format values directly ?

For instance:

# let prepare fmt = Printf.printf fmt;;
val prepare : ('a, out_channel, unit) format -> 'a = <fun>

# let sth x =
    prepare "select salary from emp where id = %d and name = %s" x;;
val sth : int -> string -> unit = <fun>

# sth 1 "Jones"
select salary from emp where id = 1 and name = Jones- : unit = ()

This is fully statically typechecked as required.

Or may be I'm missing something ?

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


-------------------
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