+
+-----------------------------------
+tcDataKindSig :: Maybe Kind -> TcM [TyVar]
+-- GADT decls can have a (perhpas partial) kind signature
+-- e.g. data T :: * -> * -> * where ...
+-- This function makes up suitable (kinded) type variables for
+-- the argument kinds, and checks that the result kind is indeed *
+tcDataKindSig Nothing = return []
+tcDataKindSig (Just kind)
+ = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
+ ; span <- getSrcSpanM
+ ; us <- newUniqueSupply
+ ; let loc = srcSpanStart span
+ uniqs = uniqsFromSupply us
+ ; return [ mk_tv loc uniq str kind
+ | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
+ where
+ (arg_kinds, res_kind) = splitKindFunTys kind
+ mk_tv loc uniq str kind = mkTyVar name kind
+ where
+ name = mkInternalName uniq occ loc
+ occ = mkOccName tvName str
+
+ names :: [String] -- a,b,c...aa,ab,ac etc
+ names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
+
+badKindSig :: Kind -> SDoc
+badKindSig kind
+ = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
+ 2 (ppr kind)