It seems to me that HsWildCardInfo is unnecessary. It is defined as newtype HsWildCardInfo pass -- See Note [The wildcard story for types] = AnonWildCard (PostRn pass (Located Name)) -- A anonymous wild card ('_'). A fresh Name is generated for -- each individual anonymous wildcard during renaming And only ever used in data HsType pass ... | HsWildCardTy (HsWildCardInfo pass) Why not just do | HsWildCardTy (PostRn pass (Located Name)) ? Am I missing something? Alan