Printf issues

Printf issues

[Till Varoquaux]

I having typing issues with sprintf:

# Printf.sprintf "%a";;
- : (unit -> '_a -> string) -> '_a -> string = <fun>

whereas:

# Printf.printf "%a";;
- : (out_channel -> '_a -> unit) -> '_a -> unit = <fun>

Am I missing something out here? If not why can't sprintf accept the
same printers as the other?

Cheers,
Till

PS: This affects Ocaml 3.9.03 and 3.10 beta, Format and Printf...

Re: [Caml-list] Printf issues

[Philippe Wang]

Till Varoquaux wrote:
> I having typing issues with sprintf:
>
> # Printf.sprintf "%a";;
> - : (unit -> '_a -> string) -> '_a -> string = <fun>
>
> whereas:
>
> # Printf.printf "%a";;
> - : (out_channel -> '_a -> unit) -> '_a -> unit = <fun>
>
> Am I missing something out here? If not why can't sprintf accept the
> same printers as the other?

Probably because it's not meant to be as you want it to be!
Why should sprintf take a function to output something on a channel 
whereas it's used to return a string?

...

Cheers,
 Philippe

Re: [Caml-list] Printf issues

[Nicolas Pouillard]

On 3/16/07, Till Varoquaux <till.varoquaux@gmail.com> wrote:
> I having typing issues with sprintf:
>
> # Printf.sprintf "%a";;
> - : (unit -> '_a -> string) -> '_a -> string = <fun>
>
> whereas:
>
> # Printf.printf "%a";;
> - : (out_channel -> '_a -> unit) -> '_a -> unit = <fun>
>
> Am I missing something out here? If not why can't sprintf accept the
> same printers as the other?

That's specified this way. It's why I don't often use sprintf but
rather these one (mainly sbprintf):

module Format_plus :
sig
  val ksbprintf : (string -> 'a) -> ('b, Format.formatter, unit, 'a)
format4 -> 'b
  val sbprintf : ('a, Format.formatter, unit, string) format4 -> 'a
end =
struct
  open Format
  let ksbprintf g fmt =
    let buff = Buffer.create 42 in
    let f = formatter_of_buffer buff in
    kfprintf (fun f -> (pp_print_flush f (); g (Buffer.contents buff))) f fmt

  let sbprintf fmt = ksbprintf (fun x -> x) fmt
end

That way it's more uniform and I can reuse the same printers for
fprintf and sbprintf.

Hope this helps,

-- 
Nicolas Pouillard