RE: [Caml-list] format strings

[David Allsopp <dra-news@metastack.com>]

Jiten Pathy wrote:
> Ok, If i am not supposed to use make_printf, then what is the recommended
> way of writing the following?
> 
> This adds a new line to given format string. In particular how do i
> manipulate the format strings passed to me?

There wasn't a vast amount of type-safe manipulation possible with format strings in the old implementation, though given the newer representation, perhaps something may come in the future. 

> open CamlinternalFormat;;
> let f (Format (fmt, _)) =
>   make_printf (fun o acc -> output_acc o (Acc_char_literal (acc, '\n'));
> ignore o) stdout End_of_acc fmt ;; val f : ('a, out_channel, unit, unit,
> unit, unit) format6 -> 'a = <fun>
> 
> utop # f "%s %d" "# " 3;;
> #  3
> - : unit = ()

However, for this "simple" manipulation there are two ways which don't touch the internals:

let f fmt = Printf.ksprintf (Printf.printf "%s\n") fmt

[that's my preference - to me it's clearer that you're wrapping the formatted output. I'd often do this to add %! as well - i.e. "%s\n%!"]

let f fmt = Printf.printf (fmt ^^ "\n")

[See http://caml.inria.fr/pub/docs/manual-ocaml-4.02/libref/Pervasives.html#6_Operationsonformatstrings]


David