Update for AST 4.06
Depend on ppxlib instead of (now deprecated) ppx_core, ppx_driver and
Somewhat surprisingly, the preprocessor didn't reject variant
inclusion despite what the documentation says, but instead would
consider that they use one rank (??). Also the generated signature
didn't match the generated code in that case. Removed completely the
support for polymorphic variant inclusion.
iterfunction generated by ppx_variants_conv and ppx_fields_conv allowed
one to give function which returned values of arbitrary types as iter function.
This feature constraint these functions to return unit.
N.B. the signature generated by the use of
@@deriving variants(resp. fields)
in interface already constrained the type to unit.
Update to follow