+ Type checking family instances
+%* *
+%************************************************************************
+
+Family instances are somewhat of a hybrid. They are processed together with
+class instance heads, but can contain data constructors and hence they share a
+lot of kinding and type checking code with ordinary algebraic data types (and
+GADTs).
+
+\begin{code}
+tcFamInstDecl :: LTyClDecl Name -> TcM TyThing
+tcFamInstDecl (L loc decl)
+ = -- Prime error recovery, set source location
+ setSrcSpan loc $
+ tcAddDeclCtxt decl $
+ do { -- type families require -XTypeFamilies and can't be in an
+ -- hs-boot file
+ ; type_families <- doptM Opt_TypeFamilies
+ ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
+ ; checkTc type_families $ badFamInstDecl (tcdLName decl)
+ ; checkTc (not is_boot) $ badBootFamInstDeclErr
+
+ -- Perform kind and type checking
+ ; tc <- tcFamInstDecl1 decl
+ ; checkValidTyCon tc -- Remember to check validity;
+ -- no recursion to worry about here
+ ; return (ATyCon tc) }
+
+tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
+
+ -- "type instance"
+tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
+ = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
+ do { -- check that the family declaration is for a synonym
+ checkTc (isOpenTyCon family) (notFamily family)
+ ; checkTc (isSynTyCon family) (wrongKindOfFamily family)
+
+ ; -- (1) kind check the right-hand side of the type equation
+ ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk)
+ -- ToDo: the ExpKind could be better
+
+ -- we need the exact same number of type parameters as the family
+ -- declaration
+ ; let famArity = tyConArity family
+ ; checkTc (length k_typats == famArity) $
+ wrongNumberOfParmsErr famArity
+
+ -- (2) type check type equation
+ ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
+ ; t_typats <- mapM tcHsKindedType k_typats
+ ; t_rhs <- tcHsKindedType k_rhs
+
+ -- (3) check the well-formedness of the instance
+ ; checkValidTypeInst t_typats t_rhs
+
+ -- (4) construct representation tycon
+ ; rep_tc_name <- newFamInstTyConName tc_name loc
+ ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
+ (typeKind t_rhs) (Just (family, t_typats))
+ }}
+
+ -- "newtype instance" and "data instance"
+tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
+ tcdCons = cons})
+ = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
+ do { -- check that the family declaration is for the right kind
+ checkTc (isOpenTyCon fam_tycon) (notFamily fam_tycon)
+ ; checkTc (isAlgTyCon fam_tycon) (wrongKindOfFamily fam_tycon)
+
+ ; -- (1) kind check the data declaration as usual
+ ; k_decl <- kcDataDecl decl k_tvs
+ ; let k_ctxt = tcdCtxt k_decl
+ k_cons = tcdCons k_decl
+
+ -- result kind must be '*' (otherwise, we have too few patterns)
+ ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
+
+ -- (2) type check indexed data type declaration
+ ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
+ ; unbox_strict <- doptM Opt_UnboxStrictFields
+
+ -- kind check the type indexes and the context
+ ; t_typats <- mapM tcHsKindedType k_typats
+ ; stupid_theta <- tcHsKindedContext k_ctxt
+
+ -- (3) Check that
+ -- (a) left-hand side contains no type family applications
+ -- (vanilla synonyms are fine, though, and we checked for
+ -- foralls earlier)
+ ; mapM_ checkTyFamFreeness t_typats
+
+ -- Check that we don't use GADT syntax in H98 world
+ ; gadt_ok <- doptM Opt_GADTs
+ ; checkTc (gadt_ok || consUseH98Syntax cons) (badGadtDecl tc_name)
+
+ -- (b) a newtype has exactly one constructor
+ ; checkTc (new_or_data == DataType || isSingleton k_cons) $
+ newtypeConError tc_name (length k_cons)
+
+ -- (4) construct representation tycon
+ ; rep_tc_name <- newFamInstTyConName tc_name loc
+ ; let ex_ok = True -- Existentials ok for type families!
+ ; fixM (\ rep_tycon -> do
+ { let orig_res_ty = mkTyConApp fam_tycon t_typats
+ ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
+ (t_tvs, orig_res_ty) k_cons
+ ; tc_rhs <-
+ case new_or_data of
+ DataType -> return (mkDataTyConRhs data_cons)
+ NewType -> ASSERT( not (null data_cons) )
+ mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
+ ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
+ False h98_syntax (Just (fam_tycon, t_typats))
+ -- We always assume that indexed types are recursive. Why?
+ -- (1) Due to their open nature, we can never be sure that a
+ -- further instance might not introduce a new recursive
+ -- dependency. (2) They are always valid loop breakers as
+ -- they involve a coercion.
+ })
+ }}
+ where
+ h98_syntax = case cons of -- All constructors have same shape
+ L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
+ _ -> True
+
+tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
+
+-- Kind checking of indexed types
+-- -
+
+-- Kind check type patterns and kind annotate the embedded type variables.
+--
+-- * Here we check that a type instance matches its kind signature, but we do
+-- not check whether there is a pattern for each type index; the latter
+-- check is only required for type synonym instances.
+
+kcIdxTyPats :: TyClDecl Name
+ -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
+ -- ^^kinded tvs ^^kinded ty pats ^^res kind
+ -> TcM a
+kcIdxTyPats decl thing_inside
+ = kcHsTyVars (tcdTyVars decl) $ \tvs ->
+ do { let tc_name = tcdLName decl
+ ; fam_tycon <- tcLookupLocatedTyCon tc_name
+ ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
+ ; hs_typats = fromJust $ tcdTyPats decl }
+
+ -- we may not have more parameters than the kind indicates
+ ; checkTc (length kinds >= length hs_typats) $
+ tooManyParmsErr (tcdLName decl)
+
+ -- type functions can have a higher-kinded result
+ ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
+ ; typats <- zipWithM kcCheckLHsType hs_typats
+ [ EK kind (EkArg (ppr tc_name) n)
+ | (kind,n) <- kinds `zip` [1..]]
+ ; thing_inside tvs typats resultKind fam_tycon
+ }
+\end{code}
+
+
+%************************************************************************
+%* *