Add string delimiter compatibility wrapper.

[aantron]

Would be quite helpful for ocsigen/tyxml#89. In particular, see: https://github.com/ocsigen/tyxml/blob/ppx/ppx/ppx_tyxml.ml#L177

[alainfrisch]

Ok in principle, but the name is not very explicit. What about quotation_delimiter, as used in Ast_helper.Const.string?

[Drup]

I think we should rather add a get_full_str that would return both the string and the delimiter. You usually want both at the same time and the multiple option wrapping are a bit annoying.

[aantron]

Will change it to whatever we agree on. I'm fine with changing the name and combining with retrieving the string, but what do you think @alainfrisch?

[alainfrisch]

My proposal:

val get_str_with_quotation_delimiter: expression -> (expression * string option) option

The name is long, but more explicit than get_full_str; and we don't want to encourage too much ppx authors to depend on the quotation delimiter (which, in its original design at least, is supposed to be purely syntactic).

[Drup]

Works for me.

[aantron]

Updated, assuming you meant (string * string option) option for the result type.