#     - : bool -> ('a, 'b, 'c, 'd, 'd, 'a) format6 = <fun>
# Characters 28-48:
  fun b -> if b then "x" else format_of_string "y";;
                              ^^^^^^^^^^^^^^^^^^^^
Error: This expression has type
         ('a, 'b, 'c, 'd, 'd, 'a) format6 =
           ('a, 'b, 'c, 'd, 'd, 'a) CamlinternalFormatBasics.format6
       but an expression was expected of type string
# - : bool -> ('a, 'b, 'a) format = <fun>
#