+isTyConableTyVar, isSkolemTyVar, isExistentialTyVar,
+ isBoxyTyVar, isMetaTyVar :: TcTyVar -> Bool
+
+isTyConableTyVar tv
+ -- True of a meta-type variable that can be filled in
+ -- with a type constructor application; in particular,
+ -- not a SigTv
+ = ASSERT( isTcTyVar tv)
+ case tcTyVarDetails tv of
+ MetaTv BoxTv _ -> True
+ MetaTv TauTv _ -> True
+ MetaTv (SigTv {}) _ -> False
+ SkolemTv {} -> False
+