Depend on ppxlib instead of (now deprecated) ppx_core, ppx_driver, ppx_metaquot and ppx_type_conv.
[%equal]; use [%compare.equal]@compare.ignore record-field attribute; ppx_compare and ppx_hash skip record fields annotated with @compare.ignore.%compare syntax for underscore (_) as meaning a comparison function that ignores both its arguments and returns zero.Ppx_core and Type_conv.