type simple = (unit, Stdlib.Format.formatter, unit) Stdlib.format
type ('a, 'b) func =
('a, Stdlib.Format.formatter, unit, 'b) Stdlib.format4 ->
'a
type 'a proc = ('a, Stdlib.Format.formatter, unit) Stdlib.format -> 'a
type 'a printer = Stdlib.Format.formatter -> 'a -> unit