[Ocaml-lib-devel] Suggestion for IO (bprintf)

[Boris Y. <bo...@ya...>]

Hi,

I've started using IO for one of my projects, but I've found it to lack a
Printf.bprintf-like function, which would permit to use "%a" formats more
easily. For example, Xml printing can be written as
let rec print_xml o xml = function
| Text t -> nwrite o t
| Tag (name, args, xml) -> bprintf "<%s%a>%a</%s> name print_args args
print_lxml xml s
and print_args o args = ...
and print_lxml o args = ...

With the current printf function, you have no such syntax.

I propose to add this function, based on the existing code of bprintf in the
ocaml distribution:

val bprintf : 'a output -> ('b, 'a output, unit, unit) format4 -> 'b

let rec bprintf dest fmt =
  let fmt = string_of_format fmt in
  let len = String.length fmt in
  let rec doprn i =
    if i >= len then Obj.magic () else
    match String.unsafe_get fmt i with
    | '%' -> Printf.scan_format fmt i cont_s cont_a cont_t cont_f cont_m
    |  c  -> write dest c; doprn (i+1)
  and cont_s s i =
    nwrite dest s; doprn i
  and cont_a printer arg i =
    printer dest arg; doprn i
  and cont_t printer i =
    printer dest; doprn i
  and cont_f i = doprn i
  and cont_m sfmt i =
    bprintf dest sfmt; doprn i
  in
    doprn 0

--
Boris

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