Re: another approach to sprintf (Re: ocaml 2.02 bug: curried printf)

[John Prevost <prevost@maya.com>]

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.