+tcLcStmt m_tc ctxt (TransformStmt stmts binders usingExpr maybeByExpr) elt_ty thing_inside = do
+ (stmts', (binders', usingExpr', maybeByExpr', thing)) <-
+ tcStmts (TransformStmtCtxt ctxt) (tcLcStmt m_tc) stmts elt_ty $ \elt_ty' -> do
+ let alphaListTy = mkTyConApp m_tc [alphaTy]
+
+ (usingExpr', maybeByExpr') <-
+ case maybeByExpr of
+ Nothing -> do
+ -- We must validate that usingExpr :: forall a. [a] -> [a]
+ usingExpr' <- tcPolyExpr usingExpr (mkForAllTy alphaTyVar (alphaListTy `mkFunTy` alphaListTy))
+ return (usingExpr', Nothing)
+ Just byExpr -> do
+ -- We must infer a type such that e :: t and then check that usingExpr :: forall a. (a -> t) -> [a] -> [a]
+ (byExpr', tTy) <- tcInferRhoNC byExpr
+ usingExpr' <- tcPolyExpr usingExpr (mkForAllTy alphaTyVar ((alphaTy `mkFunTy` tTy) `mkFunTy` (alphaListTy `mkFunTy` alphaListTy)))
+ return (usingExpr', Just byExpr')
+
+ binders' <- tcLookupLocalIds binders
+ thing <- thing_inside elt_ty'
+
+ return (binders', usingExpr', maybeByExpr', thing)
+
+ return (TransformStmt stmts' binders' usingExpr' maybeByExpr', thing)
+
+tcLcStmt m_tc ctxt (GroupStmt stmts bindersMap by using) elt_ty thing_inside
+ = do { let (bndr_names, list_bndr_names) = unzip bindersMap
+
+ ; (stmts', (bndr_ids, by', using_ty, elt_ty')) <-
+ tcStmts (TransformStmtCtxt ctxt) (tcLcStmt m_tc) stmts elt_ty $ \elt_ty' -> do
+ (by', using_ty) <- case by of
+ Nothing -> -- check that using :: forall a. [a] -> [[a]]
+ return (Nothing, mkForAllTy alphaTyVar $
+ alphaListTy `mkFunTy` alphaListListTy)
+
+ Just by_e -> -- check that using :: forall a. (a -> t) -> [a] -> [[a]]
+ -- where by :: t
+ do { (by_e', t_ty) <- tcInferRhoNC by_e
+ ; return (Just by_e', mkForAllTy alphaTyVar $
+ (alphaTy `mkFunTy` t_ty)
+ `mkFunTy` alphaListTy
+ `mkFunTy` alphaListListTy) }
+ -- Find the Ids (and hence types) of all old binders
+ bndr_ids <- tcLookupLocalIds bndr_names
+
+ return (bndr_ids, by', using_ty, elt_ty')
+
+ -- Ensure that every old binder of type b is linked up with its new binder which should have type [b]
+ ; let list_bndr_ids = zipWith mk_list_bndr list_bndr_names bndr_ids
+ bindersMap' = bndr_ids `zip` list_bndr_ids
+ -- See Note [GroupStmt binder map] in HsExpr
+
+ ; using' <- case using of
+ Left e -> do { e' <- tcPolyExpr e using_ty; return (Left e') }
+ Right e -> do { e' <- tcPolyExpr (noLoc e) using_ty; return (Right (unLoc e')) }
+
+ -- Type check the thing in the environment with these new binders and return the result
+ ; thing <- tcExtendIdEnv list_bndr_ids (thing_inside elt_ty')
+ ; return (GroupStmt stmts' bindersMap' by' using', thing) }
+ where
+ alphaListTy = mkTyConApp m_tc [alphaTy]
+ alphaListListTy = mkTyConApp m_tc [alphaListTy]
+
+ mk_list_bndr :: Name -> TcId -> TcId
+ mk_list_bndr list_bndr_name bndr_id = mkLocalId list_bndr_name (mkTyConApp m_tc [idType bndr_id])
+
+tcLcStmt _ _ stmt _ _