{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 Typecheck arrow notation -} {-# LANGUAGE RankNTypes, TupleSections #-} {-# LANGUAGE TypeFamilies #-} module TcArrows ( tcProc ) where import GhcPrelude import {-# SOURCE #-} TcExpr( tcMonoExpr, tcInferRho, tcSyntaxOp, tcCheckId, tcPolyExpr ) import HsSyn import TcMatches import TcHsSyn( hsLPatType ) import TcType import TcMType import TcBinds import TcPat import TcUnify import TcRnMonad import TcEnv import TcEvidence import Id( mkLocalId ) import Inst import Name import TysWiredIn import VarSet import TysPrim import BasicTypes( Arity ) import SrcLoc import Outputable import Util import Control.Monad {- Note [Arrow overview] ~~~~~~~~~~~~~~~~~~~~~ Here's a summary of arrows and how they typecheck. First, here's a cut-down syntax: expr ::= .... | proc pat cmd cmd ::= cmd exp -- Arrow application | \pat -> cmd -- Arrow abstraction | (| exp cmd1 ... cmdn |) -- Arrow form, n>=0 | ... -- If, case in the usual way cmd_type ::= carg_type --> type carg_type ::= () | (type, carg_type) Note that * The 'exp' in an arrow form can mention only "arrow-local" variables * An "arrow-local" variable is bound by an enclosing cmd binding form (eg arrow abstraction) * A cmd_type is here written with a funny arrow "-->", The bit on the left is a carg_type (command argument type) which itself is a nested tuple, finishing with () * The arrow-tail operator (e1 -< e2) means (| e1 <<< arr snd |) e2 ************************************************************************ * * Proc * * ************************************************************************ -} tcProc :: InPat GhcRn -> LHsCmdTop GhcRn -- proc pat -> expr -> ExpRhoType -- Expected type of whole proc expression -> TcM (OutPat GhcTcId, LHsCmdTop GhcTcId, TcCoercion) tcProc pat cmd exp_ty = newArrowScope $ do { exp_ty <- expTypeToType exp_ty -- no higher-rank stuff with arrows ; (co, (exp_ty1, res_ty)) <- matchExpectedAppTy exp_ty ; (co1, (arr_ty, arg_ty)) <- matchExpectedAppTy exp_ty1 ; let cmd_env = CmdEnv { cmd_arr = arr_ty } ; (pat', cmd') <- tcPat ProcExpr pat (mkCheckExpType arg_ty) $ tcCmdTop cmd_env cmd (unitTy, res_ty) ; let res_co = mkTcTransCo co (mkTcAppCo co1 (mkTcNomReflCo res_ty)) ; return (pat', cmd', res_co) } {- ************************************************************************ * * Commands * * ************************************************************************ -} -- See Note [Arrow overview] type CmdType = (CmdArgType, TcTauType) -- cmd_type type CmdArgType = TcTauType -- carg_type, a nested tuple data CmdEnv = CmdEnv { cmd_arr :: TcType -- arrow type constructor, of kind *->*->* } mkCmdArrTy :: CmdEnv -> TcTauType -> TcTauType -> TcTauType mkCmdArrTy env t1 t2 = mkAppTys (cmd_arr env) [t1, t2] --------------------------------------- tcCmdTop :: CmdEnv -> LHsCmdTop GhcRn -> CmdType -> TcM (LHsCmdTop GhcTcId) tcCmdTop env (L loc (HsCmdTop names cmd)) cmd_ty@(cmd_stk, res_ty) = setSrcSpan loc $ do { cmd' <- tcCmd env cmd cmd_ty ; names' <- mapM (tcSyntaxName ProcOrigin (cmd_arr env)) names ; return (L loc $ HsCmdTop (CmdTopTc cmd_stk res_ty names') cmd') } tcCmdTop _ (L _ XCmdTop{}) _ = panic "tcCmdTop" ---------------------------------------- tcCmd :: CmdEnv -> LHsCmd GhcRn -> CmdType -> TcM (LHsCmd GhcTcId) -- The main recursive function tcCmd env (L loc cmd) res_ty = setSrcSpan loc $ do { cmd' <- tc_cmd env cmd res_ty ; return (L loc cmd') } tc_cmd :: CmdEnv -> HsCmd GhcRn -> CmdType -> TcM (HsCmd GhcTcId) tc_cmd env (HsCmdPar x cmd) res_ty = do { cmd' <- tcCmd env cmd res_ty ; return (HsCmdPar x cmd') } tc_cmd env (HsCmdLet x (L l binds) (L body_loc body)) res_ty = do { (binds', body') <- tcLocalBinds binds $ setSrcSpan body_loc $ tc_cmd env body res_ty ; return (HsCmdLet x (L l binds') (L body_loc body')) } tc_cmd env in_cmd@(HsCmdCase x scrut matches) (stk, res_ty) = addErrCtxt (cmdCtxt in_cmd) $ do (scrut', scrut_ty) <- tcInferRho scrut matches' <- tcMatchesCase match_ctxt scrut_ty matches (mkCheckExpType res_ty) return (HsCmdCase x scrut' matches') where match_ctxt = MC { mc_what = CaseAlt, mc_body = mc_body } mc_body body res_ty' = do { res_ty' <- expTypeToType res_ty' ; tcCmd env body (stk, res_ty') } tc_cmd env (HsCmdIf x Nothing pred b1 b2) res_ty -- Ordinary 'if' = do { pred' <- tcMonoExpr pred (mkCheckExpType boolTy) ; b1' <- tcCmd env b1 res_ty ; b2' <- tcCmd env b2 res_ty ; return (HsCmdIf x Nothing pred' b1' b2') } tc_cmd env (HsCmdIf x (Just fun) pred b1 b2) res_ty -- Rebindable syntax for if = do { pred_ty <- newOpenFlexiTyVarTy -- For arrows, need ifThenElse :: forall r. T -> r -> r -> r -- because we're going to apply it to the environment, not -- the return value. ; (_, [r_tv]) <- tcInstSkolTyVars [alphaTyVar] ; let r_ty = mkTyVarTy r_tv ; checkTc (not (r_tv `elemVarSet` tyCoVarsOfType pred_ty)) (text "Predicate type of `ifThenElse' depends on result type") ; (pred', fun') <- tcSyntaxOp IfOrigin fun (map synKnownType [pred_ty, r_ty, r_ty]) (mkCheckExpType r_ty) $ \ _ -> tcMonoExpr pred (mkCheckExpType pred_ty) ; b1' <- tcCmd env b1 res_ty ; b2' <- tcCmd env b2 res_ty ; return (HsCmdIf x (Just fun') pred' b1' b2') } ------------------------------------------- -- Arrow application -- (f -< a) or (f -<< a) -- -- D |- fun :: a t1 t2 -- D,G |- arg :: t1 -- ------------------------ -- D;G |-a fun -< arg :: stk --> t2 -- -- D,G |- fun :: a t1 t2 -- D,G |- arg :: t1 -- ------------------------ -- D;G |-a fun -<< arg :: stk --> t2 -- -- (plus -<< requires ArrowApply) tc_cmd env cmd@(HsCmdArrApp _ fun arg ho_app lr) (_, res_ty) = addErrCtxt (cmdCtxt cmd) $ do { arg_ty <- newOpenFlexiTyVarTy ; let fun_ty = mkCmdArrTy env arg_ty res_ty ; fun' <- select_arrow_scope (tcMonoExpr fun (mkCheckExpType fun_ty)) ; arg' <- tcMonoExpr arg (mkCheckExpType arg_ty) ; return (HsCmdArrApp fun_ty fun' arg' ho_app lr) } where -- Before type-checking f, use the environment of the enclosing -- proc for the (-<) case. -- Local bindings, inside the enclosing proc, are not in scope -- inside f. In the higher-order case (-<<), they are. -- See Note [Escaping the arrow scope] in TcRnTypes select_arrow_scope tc = case ho_app of HsHigherOrderApp -> tc HsFirstOrderApp -> escapeArrowScope tc ------------------------------------------- -- Command application -- -- D,G |- exp : t -- D;G |-a cmd : (t,stk) --> res -- ----------------------------- -- D;G |-a cmd exp : stk --> res tc_cmd env cmd@(HsCmdApp x fun arg) (cmd_stk, res_ty) = addErrCtxt (cmdCtxt cmd) $ do { arg_ty <- newOpenFlexiTyVarTy ; fun' <- tcCmd env fun (mkPairTy arg_ty cmd_stk, res_ty) ; arg' <- tcMonoExpr arg (mkCheckExpType arg_ty) ; return (HsCmdApp x fun' arg') } ------------------------------------------- -- Lambda -- -- D;G,x:t |-a cmd : stk --> res -- ------------------------------ -- D;G |-a (\x.cmd) : (t,stk) --> res tc_cmd env (HsCmdLam x (MG { mg_alts = L l [L mtch_loc (match@(Match { m_pats = pats, m_grhss = grhss }))], mg_origin = origin })) (cmd_stk, res_ty) = addErrCtxt (pprMatchInCtxt match) $ do { (co, arg_tys, cmd_stk') <- matchExpectedCmdArgs n_pats cmd_stk -- Check the patterns, and the GRHSs inside ; (pats', grhss') <- setSrcSpan mtch_loc $ tcPats LambdaExpr pats (map mkCheckExpType arg_tys) $ tc_grhss grhss cmd_stk' (mkCheckExpType res_ty) ; let match' = L mtch_loc (Match { m_ext = noExt , m_ctxt = LambdaExpr, m_pats = pats' , m_grhss = grhss' }) arg_tys = map hsLPatType pats' cmd' = HsCmdLam x (MG { mg_alts = L l [match'] , mg_ext = MatchGroupTc arg_tys res_ty , mg_origin = origin }) ; return (mkHsCmdWrap (mkWpCastN co) cmd') } where n_pats = length pats match_ctxt = (LambdaExpr :: HsMatchContext Name) -- Maybe KappaExpr? pg_ctxt = PatGuard match_ctxt tc_grhss (GRHSs x grhss (L l binds)) stk_ty res_ty = do { (binds', grhss') <- tcLocalBinds binds $ mapM (wrapLocM (tc_grhs stk_ty res_ty)) grhss ; return (GRHSs x grhss' (L l binds')) } tc_grhss (XGRHSs _) _ _ = panic "tc_grhss" tc_grhs stk_ty res_ty (GRHS x guards body) = do { (guards', rhs') <- tcStmtsAndThen pg_ctxt tcGuardStmt guards res_ty $ \ res_ty -> tcCmd env body (stk_ty, checkingExpType "tc_grhs" res_ty) ; return (GRHS x guards' rhs') } tc_grhs _ _ (XGRHS _) = panic "tc_grhs" ------------------------------------------- -- Do notation tc_cmd env (HsCmdDo _ (L l stmts) ) (cmd_stk, res_ty) = do { co <- unifyType Nothing unitTy cmd_stk -- Expecting empty argument stack ; stmts' <- tcStmts ArrowExpr (tcArrDoStmt env) stmts res_ty ; return (mkHsCmdWrap (mkWpCastN co) (HsCmdDo res_ty (L l stmts') )) } ----------------------------------------------------------------- -- Arrow ``forms'' (| e c1 .. cn |) -- -- D; G |-a1 c1 : stk1 --> r1 -- ... -- D; G |-an cn : stkn --> rn -- D |- e :: forall e. a1 (e, stk1) t1 -- ... -- -> an (e, stkn) tn -- -> a (e, stk) t -- e \not\in (stk, stk1, ..., stkm, t, t1, ..., tn) -- ---------------------------------------------- -- D; G |-a (| e c1 ... cn |) : stk --> t tc_cmd env cmd@(HsCmdArrForm x expr f fixity cmd_args) (cmd_stk, res_ty) = addErrCtxt (cmdCtxt cmd) $ do { (cmd_args', cmd_tys) <- mapAndUnzipM tc_cmd_arg cmd_args -- We use alphaTyVar for 'w' ; let e_ty = mkInvForAllTy alphaTyVar $ mkFunTys cmd_tys $ mkCmdArrTy env (mkPairTy alphaTy cmd_stk) res_ty ; expr' <- tcPolyExpr expr e_ty ; return (HsCmdArrForm x expr' f fixity cmd_args') } where tc_cmd_arg :: LHsCmdTop GhcRn -> TcM (LHsCmdTop GhcTcId, TcType) tc_cmd_arg cmd = do { arr_ty <- newFlexiTyVarTy arrowTyConKind ; stk_ty <- newFlexiTyVarTy liftedTypeKind ; res_ty <- newFlexiTyVarTy liftedTypeKind ; let env' = env { cmd_arr = arr_ty } ; cmd' <- tcCmdTop env' cmd (stk_ty, res_ty) ; return (cmd', mkCmdArrTy env' (mkPairTy alphaTy stk_ty) res_ty) } tc_cmd _ (XCmd {}) _ = panic "tc_cmd" ----------------------------------------------------------------- -- Base case for illegal commands -- This is where expressions that aren't commands get rejected tc_cmd _ cmd _ = failWithTc (vcat [text "The expression", nest 2 (ppr cmd), text "was found where an arrow command was expected"]) matchExpectedCmdArgs :: Arity -> TcType -> TcM (TcCoercionN, [TcType], TcType) matchExpectedCmdArgs 0 ty = return (mkTcNomReflCo ty, [], ty) matchExpectedCmdArgs n ty = do { (co1, [ty1, ty2]) <- matchExpectedTyConApp pairTyCon ty ; (co2, tys, res_ty) <- matchExpectedCmdArgs (n-1) ty2 ; return (mkTcTyConAppCo Nominal pairTyCon [co1, co2], ty1:tys, res_ty) } {- ************************************************************************ * * Stmts * * ************************************************************************ -} -------------------------------- -- Mdo-notation -- The distinctive features here are -- (a) RecStmts, and -- (b) no rebindable syntax tcArrDoStmt :: CmdEnv -> TcCmdStmtChecker tcArrDoStmt env _ (LastStmt x rhs noret _) res_ty thing_inside = do { rhs' <- tcCmd env rhs (unitTy, res_ty) ; thing <- thing_inside (panic "tcArrDoStmt") ; return (LastStmt x rhs' noret noSyntaxExpr, thing) } tcArrDoStmt env _ (BodyStmt _ rhs _ _) res_ty thing_inside = do { (rhs', elt_ty) <- tc_arr_rhs env rhs ; thing <- thing_inside res_ty ; return (BodyStmt elt_ty rhs' noSyntaxExpr noSyntaxExpr, thing) } tcArrDoStmt env ctxt (BindStmt _ pat rhs _ _) res_ty thing_inside = do { (rhs', pat_ty) <- tc_arr_rhs env rhs ; (pat', thing) <- tcPat (StmtCtxt ctxt) pat (mkCheckExpType pat_ty) $ thing_inside res_ty ; return (mkTcBindStmt pat' rhs', thing) } tcArrDoStmt env ctxt (RecStmt { recS_stmts = stmts, recS_later_ids = later_names , recS_rec_ids = rec_names }) res_ty thing_inside = do { let tup_names = rec_names ++ filterOut (`elem` rec_names) later_names ; tup_elt_tys <- newFlexiTyVarTys (length tup_names) liftedTypeKind ; let tup_ids = zipWith mkLocalId tup_names tup_elt_tys ; tcExtendIdEnv tup_ids $ do { (stmts', tup_rets) <- tcStmtsAndThen ctxt (tcArrDoStmt env) stmts res_ty $ \ _res_ty' -> -- ToDo: res_ty not really right zipWithM tcCheckId tup_names (map mkCheckExpType tup_elt_tys) ; thing <- thing_inside res_ty -- NB: The rec_ids for the recursive things -- already scope over this part. This binding may shadow -- some of them with polymorphic things with the same Name -- (see note [RecStmt] in HsExpr) ; let rec_ids = takeList rec_names tup_ids ; later_ids <- tcLookupLocalIds later_names ; let rec_rets = takeList rec_names tup_rets ; let ret_table = zip tup_ids tup_rets ; let later_rets = [r | i <- later_ids, (j, r) <- ret_table, i == j] ; return (emptyRecStmtId { recS_stmts = stmts' , recS_later_ids = later_ids , recS_rec_ids = rec_ids , recS_ext = unitRecStmtTc { recS_later_rets = later_rets , recS_rec_rets = rec_rets , recS_ret_ty = res_ty} }, thing) }} tcArrDoStmt _ _ stmt _ _ = pprPanic "tcArrDoStmt: unexpected Stmt" (ppr stmt) tc_arr_rhs :: CmdEnv -> LHsCmd GhcRn -> TcM (LHsCmd GhcTcId, TcType) tc_arr_rhs env rhs = do { ty <- newFlexiTyVarTy liftedTypeKind ; rhs' <- tcCmd env rhs (unitTy, ty) ; return (rhs', ty) } {- ************************************************************************ * * Helpers * * ************************************************************************ -} mkPairTy :: Type -> Type -> Type mkPairTy t1 t2 = mkTyConApp pairTyCon [t1,t2] arrowTyConKind :: Kind -- *->*->* arrowTyConKind = mkFunTys [liftedTypeKind, liftedTypeKind] liftedTypeKind {- ************************************************************************ * * Errors * * ************************************************************************ -} cmdCtxt :: HsCmd GhcRn -> SDoc cmdCtxt cmd = text "In the command:" <+> ppr cmd