[Caml-list] Returning printf from a function

["Richard W.M. Jones" <rich@annexia.org>]

This is a problem we hit from time to time and I don't think I've ever
really understood why it happens.  This made up example shows the
essence:

----------------------------------------------------------------------
let get_printer out =
  if out then Printf.printf else Printf.fprintf stderr

let () =
  let printer = get_printer true in
  printer "hello\n";
  printer "goodbye %s\n" "everyone"      (* line 7 *)
----------------------------------------------------------------------

$ ocamlopt test2.ml
File "test2.ml", line 7, characters 2-9:
Error: This function has type (unit, out_channel, unit) format -> unit
       It is applied to too many arguments; maybe you forgot a `;'.

Type inference in line 6 seems to overspecify the inferred type of
printer, so that we get the error on line 7.

Why?  And how to fix it?

Rich.

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