Comment author: lavi

Well, It can be erased, but without any label:

let f ?x ~y = x,y;;

val f : ?x:'a -> y:'b -> 'a option * 'b =

f 1;;

• : 'a option * int = (None, 1)

Comment author: @garrigue

As pointed out in the note, in can be erased by passing all non-optional arguments without labels.

Comment author: elnatan

This is true, but then I think the manual needs correction: http://caml.inria.fr/pub/docs/manual-ocaml/manual006.html says, 'A function taking some optional arguments must also take at least one non-labeled argument.'

Also, when warning 6 ('labels were omitted in the application of this function.') is treated as an error, it would helpful to have the unerasable optional argument warning when an optional argument is followed by only labeled arguments.

Comment author: @garrigue

Fixed the manual, revision 11310.