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Message-ID: <48B6BDD3.7020704@ramenlabs.com>
Date: Thu, 28 Aug 2008 08:01:39 -0700
From: Dave Benjamin <dave@ramenlabs.com>
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To: Jan Kybic <kybic@fel.cvut.cz>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Run-time evaluation of a Printf format string
References: <87hc951cr9.fsf@fel.cvut.cz>
In-Reply-To: <87hc951cr9.fsf@fel.cvut.cz>
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X-Spam: no; 0.00; run-time:01 printf:01 printf:01 sprintf:01 %03:01 ocaml:01 pervasives:01 syntax:01 foo:01 buffer:01 buffer:01 val:01 abstr:01 vars:01 val:01 

Jan Kybic wrote:
>         I would need an equivalent of Printf.sprintf where the 
> format string is not constant, it is read from the command line.
> The motivation is to let the user specify a template for file names,
> such as "img%03d.png". Can this be achieved in Ocaml? It seems not, as 
> Pervasives.string_of_format only accepts constant strings.
> Or is there some external library useful for this task? 

Does it have to be printf-style formatting? If you can switch to a 
syntax like $(foo), you can use Buffer.add_substitute:

# Buffer.add_substitute;;
- : Buffer.t -> (string -> string) -> string -> unit = <fun>
# let buffer = Buffer.create 0;;
val buffer : Buffer.t = <abstr>
# let vars = ["who", "world"];;
val vars : (string * string) list = [("who", "world")]
# Buffer.add_substitute buffer
     (fun name -> List.assoc name vars)
     "hello $(who)";;
- : unit = ()
# Buffer.contents buffer;;
- : string = "hello world"


Dave