Semi optional deriving arguments using ppxlib

I’m trying to use ppxlib (actually, ppx_type_conv which now is a part of ppxlib) and my goal is to specify plugin arguments as I want. More precisely, ppxlib currently supports arguments like
[@@deriving plugin_name ~flag1 ~flag2 ...] where presence of labeled argument translates to true and absence to false.

Another way to declare arguments is to replace bool type by expression type, i.e. [@@deriving plugin_name ~arg1:e1 ~arg2:e2 ...] where the user obliged to specify expression for the labeled argument.

I want to specify plugin arguments that have type expression option and make specifying expressions optional. Can you help me to do it?

Sure. If you look at the implementation of Ppxlib.Deriving.Args.arg, you just need to set the detault field.

BTW, i just saw your post by chance, I think it is best to post such questions on the project directly