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[Caml-list] printf format strings
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Date: -- (:)
From: Hendrik Tews <tews@t...>
Subject: Re: [Caml-list] printf format strings
Jonathan Roewen <jonathan.roewen@gmail.com> writes:

   { fmt %}: convert a format string argument. The argument must have the
   same type as the internal format string fmt.
   
   And how to use it? I get Bad format `%{' in the toplevel.
   
My toplevel accepts it, but does nothing on it:

    # Printf.printf "%{%d%s%}" "kkkk\n" ;;                   
    This expression has type
      (int -> string -> 'a, 'b, 'c, int -> string -> 'a) format4
    but is here used with type (int -> string -> 'a, 'b, 'c, 'a) format4

This is expected, because kkkk has the wrong type.

    # Printf.printf "%{%d%s%}" "kk%dkk%s\n" ;;
    - : unit = <unknown constructor>

This should print something I guess. The "unknown constructor"
looks very suspicious. Maybe the %{ format is meant to generate
random strings???

    # String.escaped(Printf.sprintf "%{kkk%}" "kkk\n") ;;
    - : string =
    "\\136LŪ\\149*\\000\\000\\000 óY\\149*\\000\\000\\0000\\tī\\149*\\000\\000"

;-)


Note that there is a typo in the docs: There is no format %\(...%\):

    # Printf.printf "%\\(aaa%\\)";;
    Bad conversion %\, at char number 0 in format string ``%\(aaa%\)''

It is %(...%):

    # Printf.printf "%(aaa%)";;    
    - : ('_a, '_b, '_c, '_a) format4 -> unit = <fun>

However, it does not seem to work either:

    # Printf.printf "%(aaa%)"  "bbbb";;
    - : unit = <unknown constructor>


Bye,

Hendrik

PS. These two conversions are new, but not marked as such in the
enhanced reference manual, because they do not appear in the txt
version (which I used for the diffs).