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To: caml-list@inria.fr
Subject: Re: another approach to sprintf (Re: ocaml 2.02 bug: curried printf)
References: <19990312160017.60444@pauillac.inria.fr> <19990319174720-10695P.sumii@harp.is.s.u-tokyo.ac.jp> <19990323171753.17334@pauillac.inria.fr>
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From: John Prevost <prevost@maya.com>
Date: 24 Mar 1999 14:37:53 -0500
In-Reply-To: Xavier Leroy's message of "Tue, 23 Mar 1999 17:17:53 +0100"
Message-ID: <ya2pv5ywuem.fsf@zarya.maya.com>
User-Agent: Gnus/5.07008 (Pterodactyl Gnus v0.80) Emacs/20.3.92

Xavier Leroy <Xavier.Leroy@inria.fr> writes:

> It's a cute trick.  One drawback is that the format is not a character
> string, but needs to be expressed using special functions and infix
> operators.  On the other hand, it doesn't need the special
> typechecking rules for format strings that we have in OCaml.
> 
> With this special typechecking rules, I don't think Danvy's "partially
> evaluated" printf is any safer than OCaml's "interpreted" printf.
> 
> Also, it doesn't solve (nor makes any worse) the issues with partial
> application of printf and friends that we discussed before.

It does, however, mean that people can extend the set of patterns that
can be used in printf in a more palatable way than the %a mechanism.
Especially with neat things like Danvy's "lis" combinator.

It also allows me to take two formats and concatenate them, like this:

let foo = int $ lit " " $ int $ string
let bar = lis int $ lit "!"
let zum = foo $ bar

which you can't do with O'Caml's format strings.  (I tried to hack
something to do this once, using Obj.magic as the Printf module does.
I wasn't able to come up with anything, but I may be able to now that
I've had more experience looking at things like Danvy's printf.)

John.