dataToTag# documentation

dataToTag# is documented as getting the tag number of an enumeration, which is perfectly reasonable because it's designed to support deriving Enum. But it *appears* to work also for non-enumeration datatypes: dataToTag# Nothing = 0# dataToTag# (Just 3) = 1# Does this actually always work? If so, should that be documented, or is there a realistic possibility that its behavior will change in the future? Additionally: the documentation for dataToTag# urges readers to use GHC.Base.getTag instead. But dataToTag# is exported from the "public" GHC.Exts, whereas getTag is not. Should we add getTag to GHC.Exts, or change the documentation for dataToTag#? David