To: caml-list@inria.fr
Subject: Re: another approach to sprintf (Re: ocaml 2.02 bug: curried printf)
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"
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.
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