{- c% (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 \section[TcExpr]{Typecheck an expression} -} {-# LANGUAGE CPP #-} {-# LANGUAGE ScopedTypeVariables #-} module TcExpr ( tcPolyExpr, tcPolyExprNC, tcMonoExpr, tcMonoExprNC, tcInferRho, tcInferRhoNC, tcSyntaxOp, tcCheckId, addExprErrCtxt, getFixedTyVars ) where #include "HsVersions.h" import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket ) import THNames( liftStringName, liftName ) import HsSyn import TcHsSyn import TcRnMonad import TcUnify import BasicTypes import Inst import TcBinds ( chooseInferredQuantifiers, tcLocalBinds , tcUserTypeSig, tcExtendTyVarEnvFromSig ) import TcSimplify ( simplifyInfer ) import FamInst ( tcGetFamInstEnvs, tcLookupDataFamInst ) import FamInstEnv ( FamInstEnvs ) import RnEnv ( addUsedGRE, addNameClashErrRn , unknownSubordinateErr ) import TcEnv import TcArrows import TcMatches import TcHsType import TcPatSyn( tcPatSynBuilderOcc, nonBidirectionalErr ) import TcPat import TcMType import TcType import DsMonad import Id import IdInfo import ConLike import DataCon import PatSyn import Name import RdrName import TyCon import Type import TcEvidence import Var import VarSet import VarEnv import TysWiredIn import TysPrim( intPrimTy ) import PrimOp( tagToEnumKey ) import PrelNames import MkId ( proxyHashId ) import DynFlags import SrcLoc import Util import ListSetOps import Maybes import ErrUtils import Outputable import FastString import Control.Monad import Class(classTyCon) import Data.Function import Data.List import qualified Data.Set as Set {- ************************************************************************ * * \subsection{Main wrappers} * * ************************************************************************ -} tcPolyExpr, tcPolyExprNC :: LHsExpr Name -- Expression to type check -> TcSigmaType -- Expected type (could be a polytype) -> TcM (LHsExpr TcId) -- Generalised expr with expected type -- tcPolyExpr is a convenient place (frequent but not too frequent) -- place to add context information. -- The NC version does not do so, usually because the caller wants -- to do so himself. tcPolyExpr expr res_ty = addExprErrCtxt expr $ do { traceTc "tcPolyExpr" (ppr res_ty); tcPolyExprNC expr res_ty } tcPolyExprNC expr res_ty = do { traceTc "tcPolyExprNC" (ppr res_ty) ; (gen_fn, expr') <- tcGen GenSigCtxt res_ty $ \ _ rho -> tcMonoExprNC expr rho ; return (mkLHsWrap gen_fn expr') } --------------- tcMonoExpr, tcMonoExprNC :: LHsExpr Name -- Expression to type check -> TcRhoType -- Expected type (could be a type variable) -- Definitely no foralls at the top -> TcM (LHsExpr TcId) tcMonoExpr expr res_ty = addErrCtxt (exprCtxt expr) $ tcMonoExprNC expr res_ty tcMonoExprNC (L loc expr) res_ty = ASSERT( not (isSigmaTy res_ty) ) setSrcSpan loc $ do { expr' <- tcExpr expr res_ty ; return (L loc expr') } --------------- tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType) -- Infer a *rho*-type. This is, in effect, a special case -- for ids and partial applications, so that if -- f :: Int -> (forall a. a -> a) -> Int -- then we can infer -- f 3 :: (forall a. a -> a) -> Int -- And that in turn is useful -- (a) for the function part of any application (see tcApp) -- (b) for the special rule for '$' tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr) tcInferRhoNC (L loc expr) = setSrcSpan loc $ do { (expr', rho) <- tcInfer (tcExpr expr) ; return (L loc expr', rho) } tcUnboundId :: OccName -> TcRhoType -> TcM (HsExpr TcId) -- Typechedk an occurrence of an unbound Id -- -- Some of these started life as a true hole "_". Others might simply -- be variables that accidentally have no binding site -- -- We turn all of them into HsVar, since HsUnboundVar can't contain an -- Id; and indeed the evidence for the CHoleCan does bind it, so it's -- not unbound any more! tcUnboundId occ res_ty = do { ty <- newFlexiTyVarTy liftedTypeKind ; name <- newSysName occ ; let ev = mkLocalId name ty ; loc <- getCtLocM HoleOrigin ; let can = CHoleCan { cc_ev = CtWanted ty ev loc, cc_occ = occ , cc_hole = ExprHole } ; emitInsoluble can ; tcWrapResult (HsVar (noLoc ev)) ty res_ty } {- ************************************************************************ * * tcExpr: the main expression typechecker * * ************************************************************************ -} tcExpr :: HsExpr Name -> TcRhoType -> TcM (HsExpr TcId) tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check = pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e) tcExpr (HsVar (L _ name)) res_ty = tcCheckId name res_ty tcExpr (HsUnboundVar v) res_ty = tcUnboundId v res_ty tcExpr (HsApp e1 e2) res_ty = tcApp e1 [e2] res_ty tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit ; tcWrapResult (HsLit lit) lit_ty res_ty } tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty ; return (HsPar expr') } tcExpr (HsSCC src lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty ; return (HsSCC src lbl expr') } tcExpr (HsTickPragma src info expr) res_ty = do { expr' <- tcMonoExpr expr res_ty ; return (HsTickPragma src info expr') } tcExpr (HsCoreAnn src lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty ; return (HsCoreAnn src lbl expr') } tcExpr (HsOverLit lit) res_ty = do { lit' <- newOverloadedLit (LiteralOrigin lit) lit res_ty ; return (HsOverLit lit') } tcExpr (NegApp expr neg_expr) res_ty = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr (mkFunTy res_ty res_ty) ; expr' <- tcMonoExpr expr res_ty ; return (NegApp expr' neg_expr') } tcExpr (HsIPVar x) res_ty = do { let origin = IPOccOrigin x {- Implicit parameters must have a *tau-type* not a. type scheme. We enforce this by creating a fresh type variable as its type. (Because res_ty may not be a tau-type.) -} ; ip_ty <- newFlexiTyVarTy openTypeKind ; let ip_name = mkStrLitTy (hsIPNameFS x) ; ip_var <- emitWanted origin (mkClassPred ipClass [ip_name, ip_ty]) ; tcWrapResult (fromDict ipClass ip_name ip_ty (HsVar (noLoc ip_var))) ip_ty res_ty } where -- Coerces a dictionary for `IP "x" t` into `t`. fromDict ipClass x ty = HsWrap $ mkWpCastR $ TcCoercion $ unwrapIP $ mkClassPred ipClass [x,ty] tcExpr (HsOverLabel l) res_ty -- See Note [Type-checking overloaded labels] = do { let origin = OverLabelOrigin l ; isLabelClass <- tcLookupClass isLabelClassName ; alpha <- newFlexiTyVarTy openTypeKind ; let lbl = mkStrLitTy l pred = mkClassPred isLabelClass [lbl, alpha] ; loc <- getSrcSpanM ; var <- emitWanted origin pred ; let proxy_arg = L loc (mkHsWrap (mkWpTyApps [typeSymbolKind, lbl]) (HsVar (L loc proxyHashId))) tm = L loc (fromDict pred (HsVar (L loc var))) `HsApp` proxy_arg ; tcWrapResult tm alpha res_ty } where -- Coerces a dictionary for `IsLabel "x" t` into `Proxy# x -> t`. fromDict pred = HsWrap $ mkWpCastR $ TcCoercion $ unwrapIP pred tcExpr (HsLam match) res_ty = do { (co_fn, match') <- tcMatchLambda match res_ty ; return (mkHsWrap co_fn (HsLam match')) } tcExpr e@(HsLamCase _ matches) res_ty = do { (co_fn, [arg_ty], body_ty) <- matchExpectedFunTys msg 1 res_ty ; matches' <- tcMatchesCase match_ctxt arg_ty matches body_ty ; return $ mkHsWrapCo co_fn $ HsLamCase arg_ty matches' } where msg = sep [ ptext (sLit "The function") <+> quotes (ppr e) , ptext (sLit "requires")] match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody } tcExpr (ExprWithTySig expr sig_ty) res_ty = do { sig_info <- checkNoErrs $ -- Avoid error cascade tcUserTypeSig sig_ty Nothing ; (expr', poly_ty) <- tcExprSig expr sig_info ; (inst_wrap, rho) <- deeplyInstantiate ExprSigOrigin poly_ty ; let expr'' = mkHsWrap inst_wrap $ ExprWithTySigOut expr' sig_ty ; tcWrapResult expr'' rho res_ty } tcExpr (HsType ty) _ = failWithTc (text "Can't handle type argument:" <+> ppr ty) -- This is the syntax for type applications that I was planning -- but there are difficulties (e.g. what order for type args) -- so it's not enabled yet. -- Can't eliminate it altogether from the parser, because the -- same parser parses *patterns*. {- Note [Type-checking overloaded labels] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Recall that (in GHC.OverloadedLabels) we have class IsLabel (x :: Symbol) a where fromLabel :: Proxy# x -> a When we see an overloaded label like `#foo`, we generate a fresh variable `alpha` for the type and emit an `IsLabel "foo" alpha` constraint. Because the `IsLabel` class has a single method, it is represented by a newtype, so we can coerce `IsLabel "foo" alpha` to `Proxy# "foo" -> alpha` (just like for implicit parameters). We then apply it to `proxy#` of type `Proxy# "foo"`. That is, we translate `#foo` to `fromLabel (proxy# :: Proxy# "foo")`. -} {- ************************************************************************ * * Infix operators and sections * * ************************************************************************ Note [Left sections] ~~~~~~~~~~~~~~~~~~~~ Left sections, like (4 *), are equivalent to \ x -> (*) 4 x, or, if PostfixOperators is enabled, just (*) 4 With PostfixOperators we don't actually require the function to take two arguments at all. For example, (x `not`) means (not x); you get postfix operators! Not Haskell 98, but it's less work and kind of useful. Note [Typing rule for ($)] ~~~~~~~~~~~~~~~~~~~~~~~~~~ People write runST $ blah so much, where runST :: (forall s. ST s a) -> a that I have finally given in and written a special type-checking rule just for saturated appliations of ($). * Infer the type of the first argument * Decompose it; should be of form (arg2_ty -> res_ty), where arg2_ty might be a polytype * Use arg2_ty to typecheck arg2 Note [Typing rule for seq] ~~~~~~~~~~~~~~~~~~~~~~~~~~ We want to allow x `seq` (# p,q #) which suggests this type for seq: seq :: forall (a:*) (b:Open). a -> b -> b, with (b:Open) meaning that be can be instantiated with an unboxed tuple. The trouble is that this might accept a partially-applied 'seq', and I'm just not certain that would work. I'm only sure it's only going to work when it's fully applied, so it turns into case x of _ -> (# p,q #) So it seems more uniform to treat 'seq' as it it was a language construct. See Note [seqId magic] in MkId, and -} tcExpr (OpApp arg1 op fix arg2) res_ty | (L loc (HsVar (L lv op_name))) <- op , op_name `hasKey` seqIdKey -- Note [Typing rule for seq] = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind ; let arg2_ty = res_ty ; arg1' <- tcArg op (arg1, arg1_ty, 1) ; arg2' <- tcArg op (arg2, arg2_ty, 2) ; op_id <- tcLookupId op_name ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty]) (HsVar (L lv op_id))) ; return $ OpApp arg1' op' fix arg2' } | (L loc (HsVar (L lv op_name))) <- op , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)] = do { traceTc "Application rule" (ppr op) ; (arg1', arg1_ty) <- tcInferRho arg1 ; let doc = ptext (sLit "The first argument of ($) takes") ; (co_arg1, [arg2_ty], op_res_ty) <- matchExpectedFunTys doc 1 arg1_ty -- We have (arg1 $ arg2) -- So: arg1_ty = arg2_ty -> op_res_ty -- where arg2_ty maybe polymorphic; that's the point ; arg2' <- tcArg op (arg2, arg2_ty, 2) ; co_b <- unifyType op_res_ty res_ty -- op_res ~ res -- Make sure that the argument type has kind '*' -- ($) :: forall (a2:*) (r:Open). (a2->r) -> a2 -> r -- Eg we do not want to allow (D# $ 4.0#) Trac #5570 -- (which gives a seg fault) -- We do this by unifying with a MetaTv; but of course -- it must allow foralls in the type it unifies with (hence ReturnTv)! -- -- The *result* type can have any kind (Trac #8739), -- so we don't need to check anything for that ; a2_tv <- newReturnTyVar liftedTypeKind ; let a2_ty = mkTyVarTy a2_tv ; co_a <- unifyType arg2_ty a2_ty -- arg2 ~ a2 ; op_id <- tcLookupId op_name ; let op' = L loc (HsWrap (mkWpTyApps [a2_ty, res_ty]) (HsVar (L lv op_id))) ; return $ OpApp (mkLHsWrapCo (mkTcFunCo Nominal co_a co_b) $ mkLHsWrapCo co_arg1 arg1') op' fix (mkLHsWrapCo co_a arg2') } | (L loc (HsRecFld (Ambiguous lbl _))) <- op , Just sig_ty <- obviousSig (unLoc arg1) -- See Note [Disambiguating record fields] = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty ; sel_name <- disambiguateSelector lbl sig_tc_ty ; let op' = L loc (HsRecFld (Unambiguous lbl sel_name)) ; tcExpr (OpApp arg1 op' fix arg2) res_ty } | otherwise = do { traceTc "Non Application rule" (ppr op) ; (op', op_ty) <- tcInferFun op ; (co_fn, arg_tys, op_res_ty) <- unifyOpFunTysWrap op 2 op_ty ; co_res <- unifyType op_res_ty res_ty ; [arg1', arg2'] <- tcArgs op [arg1, arg2] arg_tys ; return $ mkHsWrapCo co_res $ OpApp arg1' (mkLHsWrapCo co_fn op') fix arg2' } -- Right sections, equivalent to \ x -> x `op` expr, or -- \ x -> op x expr tcExpr (SectionR op arg2) res_ty = do { (op', op_ty) <- tcInferFun op ; (co_fn, [arg1_ty, arg2_ty], op_res_ty) <- unifyOpFunTysWrap op 2 op_ty ; co_res <- unifyType (mkFunTy arg1_ty op_res_ty) res_ty ; arg2' <- tcArg op (arg2, arg2_ty, 2) ; return $ mkHsWrapCo co_res $ SectionR (mkLHsWrapCo co_fn op') arg2' } tcExpr (SectionL arg1 op) res_ty = do { (op', op_ty) <- tcInferFun op ; dflags <- getDynFlags -- Note [Left sections] ; let n_reqd_args | xopt Opt_PostfixOperators dflags = 1 | otherwise = 2 ; (co_fn, (arg1_ty:arg_tys), op_res_ty) <- unifyOpFunTysWrap op n_reqd_args op_ty ; co_res <- unifyType (mkFunTys arg_tys op_res_ty) res_ty ; arg1' <- tcArg op (arg1, arg1_ty, 1) ; return $ mkHsWrapCo co_res $ SectionL arg1' (mkLHsWrapCo co_fn op') } tcExpr (ExplicitTuple tup_args boxity) res_ty | all tupArgPresent tup_args = do { let tup_tc = tupleTyCon boxity (length tup_args) ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty ; tup_args1 <- tcTupArgs tup_args arg_tys ; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) } | otherwise = -- The tup_args are a mixture of Present and Missing (for tuple sections) do { let kind = case boxity of { Boxed -> liftedTypeKind ; Unboxed -> openTypeKind } arity = length tup_args tup_tc = tupleTyCon boxity arity ; arg_tys <- newFlexiTyVarTys (tyConArity tup_tc) kind ; let actual_res_ty = mkFunTys [ty | (ty, L _ (Missing _)) <- arg_tys `zip` tup_args] (mkTyConApp tup_tc arg_tys) ; coi <- unifyType actual_res_ty res_ty -- Handle tuple sections where ; tup_args1 <- tcTupArgs tup_args arg_tys ; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) } tcExpr (ExplicitList _ witness exprs) res_ty = case witness of Nothing -> do { (coi, elt_ty) <- matchExpectedListTy res_ty ; exprs' <- mapM (tc_elt elt_ty) exprs ; return $ mkHsWrapCo coi (ExplicitList elt_ty Nothing exprs') } Just fln -> do { list_ty <- newFlexiTyVarTy liftedTypeKind ; fln' <- tcSyntaxOp ListOrigin fln (mkFunTys [intTy, list_ty] res_ty) ; (coi, elt_ty) <- matchExpectedListTy list_ty ; exprs' <- mapM (tc_elt elt_ty) exprs ; return $ mkHsWrapCo coi (ExplicitList elt_ty (Just fln') exprs') } where tc_elt elt_ty expr = tcPolyExpr expr elt_ty tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty ; exprs' <- mapM (tc_elt elt_ty) exprs ; return $ mkHsWrapCo coi (ExplicitPArr elt_ty exprs') } where tc_elt elt_ty expr = tcPolyExpr expr elt_ty {- ************************************************************************ * * Let, case, if, do * * ************************************************************************ -} tcExpr (HsLet (L l binds) expr) res_ty = do { (binds', expr') <- tcLocalBinds binds $ tcMonoExpr expr res_ty ; return (HsLet (L l binds') expr') } tcExpr (HsCase scrut matches) exp_ty = do { -- We used to typecheck the case alternatives first. -- The case patterns tend to give good type info to use -- when typechecking the scrutinee. For example -- case (map f) of -- (x:xs) -> ... -- will report that map is applied to too few arguments -- -- But now, in the GADT world, we need to typecheck the scrutinee -- first, to get type info that may be refined in the case alternatives (scrut', scrut_ty) <- tcInferRho scrut ; traceTc "HsCase" (ppr scrut_ty) ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty ; return (HsCase scrut' matches') } where match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody } tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if' = do { pred' <- tcMonoExpr pred boolTy ; b1' <- tcMonoExpr b1 res_ty ; b2' <- tcMonoExpr b2 res_ty ; return (HsIf Nothing pred' b1' b2') } tcExpr (HsIf (Just fun) pred b1 b2) res_ty -- Note [Rebindable syntax for if] = do { pred_ty <- newFlexiTyVarTy openTypeKind ; b1_ty <- newFlexiTyVarTy openTypeKind ; b2_ty <- newFlexiTyVarTy openTypeKind ; let if_ty = mkFunTys [pred_ty, b1_ty, b2_ty] res_ty ; fun' <- tcSyntaxOp IfOrigin fun if_ty ; pred' <- tcMonoExpr pred pred_ty ; b1' <- tcMonoExpr b1 b1_ty ; b2' <- tcMonoExpr b2 b2_ty -- Fundamentally we are just typing (ifThenElse e1 e2 e3) -- so maybe we should use the code for function applications -- (which would allow ifThenElse to be higher rank). -- But it's a little awkward, so I'm leaving it alone for now -- and it maintains uniformity with other rebindable syntax ; return (HsIf (Just fun') pred' b1' b2') } tcExpr (HsMultiIf _ alts) res_ty = do { alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts ; return $ HsMultiIf res_ty alts' } where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody } tcExpr (HsDo do_or_lc stmts _) res_ty = tcDoStmts do_or_lc stmts res_ty tcExpr (HsProc pat cmd) res_ty = do { (pat', cmd', coi) <- tcProc pat cmd res_ty ; return $ mkHsWrapCo coi (HsProc pat' cmd') } tcExpr (HsStatic expr) res_ty = do { staticPtrTyCon <- tcLookupTyCon staticPtrTyConName ; (co, [expr_ty]) <- matchExpectedTyConApp staticPtrTyCon res_ty ; (expr', lie) <- captureConstraints $ addErrCtxt (hang (ptext (sLit "In the body of a static form:")) 2 (ppr expr) ) $ tcPolyExprNC expr expr_ty -- Require the type of the argument to be Typeable. -- The evidence is not used, but asking the constraint ensures that -- the current implementation is as restrictive as future versions -- of the StaticPointers extension. ; typeableClass <- tcLookupClass typeableClassName ; _ <- emitWanted StaticOrigin $ mkTyConApp (classTyCon typeableClass) [liftedTypeKind, expr_ty] -- Insert the static form in a global list for later validation. ; stWC <- tcg_static_wc <$> getGblEnv ; updTcRef stWC (andWC lie) ; return $ mkHsWrapCo co $ HsStatic expr' } {- Note [Rebindable syntax for if] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The rebindable syntax for 'if' uses the most flexible possible type for conditionals: ifThenElse :: p -> b1 -> b2 -> res to support expressions like this: ifThenElse :: Maybe a -> (a -> b) -> b -> b ifThenElse (Just a) f _ = f a ifThenElse Nothing _ e = e example :: String example = if Just 2 then \v -> show v else "No value" ************************************************************************ * * Record construction and update * * ************************************************************************ -} tcExpr (RecordCon { rcon_con_name = L loc con_name, rcon_flds = rbinds }) res_ty = do { con_like <- tcLookupConLike con_name -- Check for missing fields ; checkMissingFields con_like rbinds ; (con_expr, con_tau) <- tcInferId con_name ; let arity = conLikeArity con_like (arg_tys, actual_res_ty) = tcSplitFunTysN con_tau arity ; case conLikeWrapId_maybe con_like of Nothing -> nonBidirectionalErr (conLikeName con_like) Just con_id -> do { co_res <- unifyType actual_res_ty res_ty ; rbinds' <- tcRecordBinds con_like arg_tys rbinds ; return $ mkHsWrapCo co_res $ RecordCon { rcon_con_name = L loc con_id , rcon_con_expr = con_expr , rcon_con_like = con_like , rcon_flds = rbinds' } } } {- Note [Type of a record update] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The main complication with RecordUpd is that we need to explicitly handle the *non-updated* fields. Consider: data T a b c = MkT1 { fa :: a, fb :: (b,c) } | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c } | MkT3 { fd :: a } upd :: T a b c -> (b',c) -> T a b' c upd t x = t { fb = x} The result type should be (T a b' c) not (T a b c), because 'b' *is not* mentioned in a non-updated field not (T a b' c'), because 'c' *is* mentioned in a non-updated field NB that it's not good enough to look at just one constructor; we must look at them all; cf Trac #3219 After all, upd should be equivalent to: upd t x = case t of MkT1 p q -> MkT1 p x MkT2 a b -> MkT2 p b MkT3 d -> error ... So we need to give a completely fresh type to the result record, and then constrain it by the fields that are *not* updated ("p" above). We call these the "fixed" type variables, and compute them in getFixedTyVars. Note that because MkT3 doesn't contain all the fields being updated, its RHS is simply an error, so it doesn't impose any type constraints. Hence the use of 'relevant_cont'. Note [Implicit type sharing] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ We also take into account any "implicit" non-update fields. For example data T a b where { MkT { f::a } :: T a a; ... } So the "real" type of MkT is: forall ab. (a~b) => a -> T a b Then consider upd t x = t { f=x } We infer the type upd :: T a b -> a -> T a b upd (t::T a b) (x::a) = case t of { MkT (co:a~b) (_:a) -> MkT co x } We can't give it the more general type upd :: T a b -> c -> T c b Note [Criteria for update] ~~~~~~~~~~~~~~~~~~~~~~~~~~ We want to allow update for existentials etc, provided the updated field isn't part of the existential. For example, this should be ok. data T a where { MkT { f1::a, f2::b->b } :: T a } f :: T a -> b -> T b f t b = t { f1=b } The criterion we use is this: The types of the updated fields mention only the universally-quantified type variables of the data constructor NB: this is not (quite) the same as being a "naughty" record selector (See Note [Naughty record selectors]) in TcTyClsDecls), at least in the case of GADTs. Consider data T a where { MkT :: { f :: a } :: T [a] } Then f is not "naughty" because it has a well-typed record selector. But we don't allow updates for 'f'. (One could consider trying to allow this, but it makes my head hurt. Badly. And no one has asked for it.) In principle one could go further, and allow g :: T a -> T a g t = t { f2 = \x -> x } because the expression is polymorphic...but that seems a bridge too far. Note [Data family example] ~~~~~~~~~~~~~~~~~~~~~~~~~~ data instance T (a,b) = MkT { x::a, y::b } ---> data :TP a b = MkT { a::a, y::b } coTP a b :: T (a,b) ~ :TP a b Suppose r :: T (t1,t2), e :: t3 Then r { x=e } :: T (t3,t1) ---> case r |> co1 of MkT x y -> MkT e y |> co2 where co1 :: T (t1,t2) ~ :TP t1 t2 co2 :: :TP t3 t2 ~ T (t3,t2) The wrapping with co2 is done by the constructor wrapper for MkT Outgoing invariants ~~~~~~~~~~~~~~~~~~~ In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys): * cons are the data constructors to be updated * in_inst_tys, out_inst_tys have same length, and instantiate the *representation* tycon of the data cons. In Note [Data family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2] Note [Mixed Record Field Updates] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider the following pattern synonym. data MyRec = MyRec { foo :: Int, qux :: String } pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2} This allows updates such as the following updater :: MyRec -> MyRec updater a = a {f1 = 1 } It would also make sense to allow the following update (which we reject). updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two" This leads to confusing behaviour when the selectors in fact refer the same field. updater a = a {f1 = 1, foo = 2} ==? ??? For this reason, we reject a mixture of pattern synonym and normal record selectors in the same update block. Although of course we still allow the following. updater a = (a {f1 = 1}) {foo = 2} > updater (MyRec 0 "str") MyRec 2 "str" -} tcExpr (RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty = ASSERT( notNull rbnds ) do { -- STEP -2: typecheck the record_expr, the record to bd updated (record_expr', record_tau) <- tcInferFun record_expr -- STEP -1 See Note [Disambiguating record fields] -- After this we know that rbinds is unambiguous ; rbinds <- disambiguateRecordBinds record_expr record_tau rbnds res_ty ; let upd_flds = map (unLoc . hsRecFieldLbl . unLoc) rbinds upd_fld_occs = map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc) upd_flds sel_ids = map selectorAmbiguousFieldOcc upd_flds -- STEP 0 -- Check that the field names are really field names -- and they are all field names for proper records or -- all field names for pattern synonyms. ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name) | fld <- rbinds, -- Excludes class ops let L loc sel_id = hsRecUpdFieldId (unLoc fld), not (isRecordSelector sel_id), let fld_name = idName sel_id ] ; unless (null bad_guys) (sequence bad_guys >> failM) -- See note [Mixed Record Selectors] ; let (data_sels, pat_syn_sels) = partition isDataConRecordSelector sel_ids ; MASSERT( all isPatSynRecordSelector pat_syn_sels ) ; checkTc ( null data_sels || null pat_syn_sels ) ( mixedSelectors data_sels pat_syn_sels ) -- STEP 1 -- Figure out the tycon and data cons from the first field name ; let -- It's OK to use the non-tc splitters here (for a selector) sel_id : _ = sel_ids mtycon :: Maybe TyCon mtycon = case idDetails sel_id of RecSelId (RecSelData tycon) _ -> Just tycon _ -> Nothing con_likes :: [ConLike] con_likes = case idDetails sel_id of RecSelId (RecSelData tc) _ -> map RealDataCon (tyConDataCons tc) RecSelId (RecSelPatSyn ps) _ -> [PatSynCon ps] _ -> panic "tcRecordUpd" -- NB: for a data type family, the tycon is the instance tycon relevant_cons = conLikesWithFields con_likes upd_fld_occs -- A constructor is only relevant to this process if -- it contains *all* the fields that are being updated -- Other ones will cause a runtime error if they occur -- Step 2 -- Check that at least one constructor has all the named fields -- i.e. has an empty set of bad fields returned by badFields ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds con_likes) -- Take apart a representative constructor ; let con1 = ASSERT( not (null relevant_cons) ) head relevant_cons (con1_tvs, _, _, _prov_theta, req_theta, con1_arg_tys, _) = conLikeFullSig con1 con1_flds = map flLabel $ conLikeFieldLabels con1 con1_tv_tys = mkTyVarTys con1_tvs con1_res_ty = case mtycon of Just tc -> mkFamilyTyConApp tc con1_tv_tys Nothing -> conLikeResTy con1 con1_tv_tys -- Check that we're not dealing with a unidirectional pattern -- synonym ; unless (isJust $ conLikeWrapId_maybe con1) (nonBidirectionalErr (conLikeName con1)) -- STEP 3 Note [Criteria for update] -- Check that each updated field is polymorphic; that is, its type -- mentions only the universally-quantified variables of the data con ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys bad_upd_flds = filter bad_fld flds1_w_tys con1_tv_set = mkVarSet con1_tvs bad_fld (fld, ty) = fld `elem` upd_fld_occs && not (tyVarsOfType ty `subVarSet` con1_tv_set) ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds) -- STEP 4 Note [Type of a record update] -- Figure out types for the scrutinee and result -- Both are of form (T a b c), with fresh type variables, but with -- common variables where the scrutinee and result must have the same type -- These are variables that appear in *any* arg of *any* of the -- relevant constructors *except* in the updated fields -- ; let fixed_tvs = getFixedTyVars upd_fld_occs con1_tvs relevant_cons is_fixed_tv tv = tv `elemVarSet` fixed_tvs mk_inst_ty :: TvSubst -> (TKVar, TcType) -> TcM (TvSubst, TcType) -- Deals with instantiation of kind variables -- c.f. TcMType.tcInstTyVars mk_inst_ty subst (tv, result_inst_ty) | is_fixed_tv tv -- Same as result type = return (extendTvSubst subst tv result_inst_ty, result_inst_ty) | otherwise -- Fresh type, of correct kind = do { new_ty <- newFlexiTyVarTy (TcType.substTy subst (tyVarKind tv)) ; return (extendTvSubst subst tv new_ty, new_ty) } ; (result_subst, con1_tvs') <- tcInstTyVars con1_tvs ; let result_inst_tys = mkTyVarTys con1_tvs' ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty emptyTvSubst (con1_tvs `zip` result_inst_tys) ; let rec_res_ty = TcType.substTy result_subst con1_res_ty scrut_ty = TcType.substTy scrut_subst con1_res_ty con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys ; co_res <- unifyType rec_res_ty res_ty ; co_scrut <- unifyType record_tau scrut_ty -- STEP 5 -- Typecheck the bindings ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds -- STEP 6: Deal with the stupid theta ; let theta' = substTheta scrut_subst (conLikeStupidTheta con1) ; instStupidTheta RecordUpdOrigin theta' -- Step 7: make a cast for the scrutinee, in the -- case that it's from a data family ; let fam_co :: HsWrapper -- RepT t1 .. tn ~R scrut_ty fam_co | Just tycon <- mtycon , Just co_con <- tyConFamilyCoercion_maybe tycon = mkWpCastR (mkTcUnbranchedAxInstCo co_con scrut_inst_tys) | otherwise = idHsWrapper -- Step 8: Check that the req constraints are satisfied -- For normal data constructors req_theta is empty but we must do -- this check for pattern synonyms. ; let req_theta' = substTheta scrut_subst req_theta ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta' -- Phew! ; return $ mkHsWrapCo co_res $ RecordUpd { rupd_expr = mkLHsWrap fam_co (mkLHsWrapCo co_scrut record_expr') , rupd_flds = rbinds' , rupd_cons = relevant_cons, rupd_in_tys = scrut_inst_tys , rupd_out_tys = result_inst_tys, rupd_wrap = req_wrap } } tcExpr (HsRecFld f) res_ty = tcCheckRecSelId f res_ty {- ************************************************************************ * * Arithmetic sequences e.g. [a,b..] and their parallel-array counterparts e.g. [: a,b.. :] * * ************************************************************************ -} tcExpr (ArithSeq _ witness seq) res_ty = tcArithSeq witness seq res_ty tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty ; expr1' <- tcPolyExpr expr1 elt_ty ; expr2' <- tcPolyExpr expr2 elt_ty ; enumFromToP <- initDsTc $ dsDPHBuiltin enumFromToPVar ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq) (idName enumFromToP) elt_ty ; return $ mkHsWrapCo coi (PArrSeq enum_from_to (FromTo expr1' expr2')) } tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty ; expr1' <- tcPolyExpr expr1 elt_ty ; expr2' <- tcPolyExpr expr2 elt_ty ; expr3' <- tcPolyExpr expr3 elt_ty ; enumFromThenToP <- initDsTc $ dsDPHBuiltin enumFromThenToPVar ; eft <- newMethodFromName (PArrSeqOrigin seq) (idName enumFromThenToP) elt_ty -- !!!FIXME: chak ; return $ mkHsWrapCo coi (PArrSeq eft (FromThenTo expr1' expr2' expr3')) } tcExpr (PArrSeq _ _) _ = panic "TcExpr.tcExpr: Infinite parallel array!" -- the parser shouldn't have generated it and the renamer shouldn't have -- let it through {- ************************************************************************ * * Template Haskell * * ************************************************************************ -} tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty tcExpr (HsBracket brack) res_ty = tcTypedBracket brack res_ty tcExpr (HsRnBracketOut brack ps) res_ty = tcUntypedBracket brack ps res_ty {- ************************************************************************ * * Catch-all * * ************************************************************************ -} tcExpr other _ = pprPanic "tcMonoExpr" (ppr other) -- Include ArrForm, ArrApp, which shouldn't appear at all -- Also HsTcBracketOut, HsQuasiQuoteE {- ************************************************************************ * * Arithmetic sequences [a..b] etc * * ************************************************************************ -} tcArithSeq :: Maybe (SyntaxExpr Name) -> ArithSeqInfo Name -> TcRhoType -> TcM (HsExpr TcId) tcArithSeq witness seq@(From expr) res_ty = do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr' <- tcPolyExpr expr elt_ty ; enum_from <- newMethodFromName (ArithSeqOrigin seq) enumFromName elt_ty ; return $ mkHsWrapCo coi (ArithSeq enum_from wit' (From expr')) } tcArithSeq witness seq@(FromThen expr1 expr2) res_ty = do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcPolyExpr expr1 elt_ty ; expr2' <- tcPolyExpr expr2 elt_ty ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq) enumFromThenName elt_ty ; return $ mkHsWrapCo coi (ArithSeq enum_from_then wit' (FromThen expr1' expr2')) } tcArithSeq witness seq@(FromTo expr1 expr2) res_ty = do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcPolyExpr expr1 elt_ty ; expr2' <- tcPolyExpr expr2 elt_ty ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq) enumFromToName elt_ty ; return $ mkHsWrapCo coi (ArithSeq enum_from_to wit' (FromTo expr1' expr2')) } tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty = do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcPolyExpr expr1 elt_ty ; expr2' <- tcPolyExpr expr2 elt_ty ; expr3' <- tcPolyExpr expr3 elt_ty ; eft <- newMethodFromName (ArithSeqOrigin seq) enumFromThenToName elt_ty ; return $ mkHsWrapCo coi (ArithSeq eft wit' (FromThenTo expr1' expr2' expr3')) } ----------------- arithSeqEltType :: Maybe (SyntaxExpr Name) -> TcRhoType -> TcM (TcCoercion, TcType, Maybe (SyntaxExpr Id)) arithSeqEltType Nothing res_ty = do { (coi, elt_ty) <- matchExpectedListTy res_ty ; return (coi, elt_ty, Nothing) } arithSeqEltType (Just fl) res_ty = do { list_ty <- newFlexiTyVarTy liftedTypeKind ; fl' <- tcSyntaxOp ListOrigin fl (mkFunTy list_ty res_ty) ; (coi, elt_ty) <- matchExpectedListTy list_ty ; return (coi, elt_ty, Just fl') } {- ************************************************************************ * * Applications * * ************************************************************************ -} tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args -> TcRhoType -> TcM (HsExpr TcId) -- Translated fun and args tcApp (L _ (HsPar e)) args res_ty = tcApp e args res_ty tcApp (L _ (HsApp e1 e2)) args res_ty = tcApp e1 (e2:args) res_ty -- Accumulate the arguments tcApp (L loc (HsVar (L _ fun))) args res_ty | fun `hasKey` tagToEnumKey , [arg] <- args = tcTagToEnum loc fun arg res_ty | fun `hasKey` seqIdKey , [arg1,arg2] <- args = tcSeq loc fun arg1 arg2 res_ty -- Look for applications of ambiguous record selectors to arguments -- with type signatures, see Note [Disambiguating record fields] tcApp (L loc (HsRecFld (Ambiguous lbl _))) args@(L _ arg:_) res_ty | Just sig_ty <- obviousSig arg = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty ; sel_name <- disambiguateSelector lbl sig_tc_ty ; tcApp (L loc (HsRecFld (Unambiguous lbl sel_name))) args res_ty } tcApp fun args res_ty = do { -- Type-check the function ; (fun1, fun_tau) <- tcInferFun fun -- Extract its argument types ; (co_fun, expected_arg_tys, actual_res_ty) <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau -- Typecheck the result, thereby propagating -- info (if any) from result into the argument types -- Both actual_res_ty and res_ty are deeply skolemised -- Rather like tcWrapResult, but (perhaps for historical reasons) -- we do this before typechecking the arguments ; wrap_res <- addErrCtxtM (funResCtxt True (unLoc fun) actual_res_ty res_ty) $ tcSubTypeDS_NC GenSigCtxt actual_res_ty res_ty -- Typecheck the arguments ; args1 <- tcArgs fun args expected_arg_tys -- Assemble the result ; let fun2 = mkLHsWrapCo co_fun fun1 app = mkLHsWrap wrap_res (foldl mkHsApp fun2 args1) ; return (unLoc app) } mk_app_msg :: LHsExpr Name -> SDoc mk_app_msg fun = sep [ ptext (sLit "The function") <+> quotes (ppr fun) , ptext (sLit "is applied to")] ---------------- tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType) -- Infer and instantiate the type of a function tcInferFun (L loc (HsVar (L _ name))) = do { (fun, ty) <- setSrcSpan loc (tcInferId name) -- Don't wrap a context around a plain Id ; return (L loc fun, ty) } tcInferFun (L loc (HsRecFld f)) = do { (fun, ty) <- setSrcSpan loc (tcInferRecSelId f) -- Don't wrap a context around a plain Id ; return (L loc fun, ty) } tcInferFun fun = do { (fun, fun_ty) <- tcInfer (tcMonoExpr fun) -- Zonk the function type carefully, to expose any polymorphism -- E.g. (( \(x::forall a. a->a). blah ) e) -- We can see the rank-2 type of the lambda in time to generalise e ; fun_ty' <- zonkTcType fun_ty ; (wrap, rho) <- deeplyInstantiate AppOrigin fun_ty' ; return (mkLHsWrap wrap fun, rho) } ---------------- tcArgs :: LHsExpr Name -- The function (for error messages) -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types -> TcM [LHsExpr TcId] -- Resulting args tcArgs fun args expected_arg_tys = mapM (tcArg fun) (zip3 args expected_arg_tys [1..]) ---------------- tcArg :: LHsExpr Name -- The function (for error messages) -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type -> TcM (LHsExpr TcId) -- Resulting argument tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no) (tcPolyExprNC arg ty) ---------------- tcTupArgs :: [LHsTupArg Name] -> [TcSigmaType] -> TcM [LHsTupArg TcId] tcTupArgs args tys = ASSERT( equalLength args tys ) mapM go (args `zip` tys) where go (L l (Missing {}), arg_ty) = return (L l (Missing arg_ty)) go (L l (Present expr), arg_ty) = do { expr' <- tcPolyExpr expr arg_ty ; return (L l (Present expr')) } ---------------- unifyOpFunTysWrap :: LHsExpr Name -> Arity -> TcRhoType -> TcM (TcCoercion, [TcSigmaType], TcRhoType) -- A wrapper for matchExpectedFunTys unifyOpFunTysWrap op arity ty = matchExpectedFunTys herald arity ty where herald = ptext (sLit "The operator") <+> quotes (ppr op) <+> ptext (sLit "takes") --------------------------- tcSyntaxOp :: CtOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId) -- Typecheck a syntax operator, checking that it has the specified type -- The operator is always a variable at this stage (i.e. renamer output) -- This version assumes res_ty is a monotype tcSyntaxOp orig (HsVar (L _ op)) res_ty = do { (expr, rho) <- tcInferIdWithOrig orig (nameRdrName op) op ; tcWrapResult expr rho res_ty } tcSyntaxOp _ other _ = pprPanic "tcSyntaxOp" (ppr other) {- Note [Push result type in] ~~~~~~~~~~~~~~~~~~~~~~~~~~ Unify with expected result before type-checking the args so that the info from res_ty percolates to args. This is when we might detect a too-few args situation. (One can think of cases when the opposite order would give a better error message.) experimenting with putting this first. Here's an example where it actually makes a real difference class C t a b | t a -> b instance C Char a Bool data P t a = forall b. (C t a b) => MkP b data Q t = MkQ (forall a. P t a) f1, f2 :: Q Char; f1 = MkQ (MkP True) f2 = MkQ (MkP True :: forall a. P Char a) With the change, f1 will type-check, because the 'Char' info from the signature is propagated into MkQ's argument. With the check in the other order, the extra signature in f2 is reqd. ************************************************************************ * * Expressions with a type signature expr :: type * * ********************************************************************* -} tcExprSig :: LHsExpr Name -> TcIdSigInfo -> TcM (LHsExpr TcId, TcType) tcExprSig expr sig@(TISI { sig_bndr = s_bndr , sig_skols = skol_prs , sig_theta = theta , sig_tau = tau }) | null skol_prs -- Fast path when there is no quantification at all , null theta , CompleteSig {} <- s_bndr = do { expr' <- tcPolyExprNC expr tau ; return (expr', tau) } | CompleteSig poly_id <- s_bndr = do { given <- newEvVars theta ; (ev_binds, expr') <- checkConstraints skol_info skol_tvs given $ tcExtendTyVarEnvFromSig sig $ tcPolyExprNC expr tau ; let poly_wrap = mkWpTyLams skol_tvs <.> mkWpLams given <.> mkWpLet ev_binds ; return (mkLHsWrap poly_wrap expr', idType poly_id) } | PartialSig { sig_name = name } <- s_bndr = do { (tclvl, wanted, expr') <- pushLevelAndCaptureConstraints $ tcExtendTyVarEnvFromSig sig $ tcPolyExprNC expr tau ; (qtvs, givens, ev_binds) <- simplifyInfer tclvl False [sig] [(name, tau)] wanted ; tau <- zonkTcType tau ; let inferred_theta = map evVarPred givens tau_tvs = tyVarsOfType tau ; (my_tv_set, my_theta) <- chooseInferredQuantifiers inferred_theta tau_tvs (Just sig) ; let my_tvs = filter (`elemVarSet` my_tv_set) qtvs -- Maintain original order inferred_sigma = mkSigmaTy qtvs inferred_theta tau my_sigma = mkSigmaTy my_tvs my_theta tau ; wrap <- if inferred_sigma `eqType` my_sigma then return idHsWrapper -- Fast path; also avoids complaint when we infer -- an ambiguouse type and have AllowAmbiguousType -- e..g infer x :: forall a. F a -> Int else tcSubType_NC ExprSigCtxt inferred_sigma my_sigma ; let poly_wrap = wrap <.> mkWpTyLams qtvs <.> mkWpLams givens <.> mkWpLet ev_binds ; return (mkLHsWrap poly_wrap expr', mkSigmaTy qtvs theta tau) } | otherwise = panic "tcExprSig" -- Can't happen where skol_info = SigSkol ExprSigCtxt (mkPhiTy theta tau) skol_tvs = map snd skol_prs {- ********************************************************************* * * tcInferId * * ********************************************************************* -} tcCheckId :: Name -> TcRhoType -> TcM (HsExpr TcId) tcCheckId name res_ty = do { (expr, actual_res_ty) <- tcInferId name ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty]) ; addErrCtxtM (funResCtxt False (HsVar (noLoc name)) actual_res_ty res_ty) $ tcWrapResult expr actual_res_ty res_ty } tcCheckRecSelId :: AmbiguousFieldOcc Name -> TcRhoType -> TcM (HsExpr TcId) tcCheckRecSelId f@(Unambiguous _ _) res_ty = do { (expr, actual_res_ty) <- tcInferRecSelId f ; addErrCtxtM (funResCtxt False (HsRecFld f) actual_res_ty res_ty) $ tcWrapResult expr actual_res_ty res_ty } tcCheckRecSelId (Ambiguous lbl _) res_ty = case tcSplitFunTy_maybe res_ty of Nothing -> ambiguousSelector lbl Just (arg, _) -> do { sel_name <- disambiguateSelector lbl arg ; tcCheckRecSelId (Unambiguous lbl sel_name) res_ty } ------------------------ tcInferId :: Name -> TcM (HsExpr TcId, TcRhoType) -- Infer type, and deeply instantiate tcInferId n = tcInferIdWithOrig (OccurrenceOf n) (nameRdrName n) n tcInferRecSelId :: AmbiguousFieldOcc Name -> TcM (HsExpr TcId, TcRhoType) tcInferRecSelId (Unambiguous lbl sel) = tcInferIdWithOrig (OccurrenceOfRecSel lbl) lbl sel tcInferRecSelId (Ambiguous lbl _) = ambiguousSelector lbl ------------------------ tcInferIdWithOrig :: CtOrigin -> RdrName -> Name -> TcM (HsExpr TcId, TcRhoType) -- Look up an occurrence of an Id, and instantiate it (deeply) tcInferIdWithOrig orig lbl id_name | id_name `hasKey` tagToEnumKey = failWithTc (ptext (sLit "tagToEnum# must appear applied to one argument")) -- tcApp catches the case (tagToEnum# arg) | id_name `hasKey` assertIdKey = do { dflags <- getDynFlags ; if gopt Opt_IgnoreAsserts dflags then tc_infer_id orig lbl id_name else tc_infer_assert orig } | otherwise = tc_infer_id orig lbl id_name tc_infer_assert :: CtOrigin -> TcM (HsExpr TcId, TcRhoType) -- Deal with an occurrence of 'assert' -- See Note [Adding the implicit parameter to 'assert'] tc_infer_assert orig = do { assert_error_id <- tcLookupId assertErrorName ; (wrap, id_rho) <- deeplyInstantiate orig (idType assert_error_id) ; return (mkHsWrap wrap (HsVar (noLoc assert_error_id)), id_rho) } tc_infer_id :: CtOrigin -> RdrName -> Name -> TcM (HsExpr TcId, TcRhoType) -- Return type is deeply instantiated tc_infer_id orig lbl id_name = do { thing <- tcLookup id_name ; case thing of ATcId { tct_id = id } -> do { check_naughty id -- Note [Local record selectors] ; checkThLocalId id ; inst_normal_id id } AGlobal (AnId id) -> do { check_naughty id ; inst_normal_id id } -- A global cannot possibly be ill-staged -- nor does it need the 'lifting' treatment -- hence no checkTh stuff here AGlobal (AConLike cl) -> case cl of RealDataCon con -> inst_data_con con PatSynCon ps -> tcPatSynBuilderOcc orig ps _ -> failWithTc $ ppr thing <+> ptext (sLit "used where a value identifier was expected") } where inst_normal_id id = do { (wrap, rho) <- deeplyInstantiate orig (idType id) ; return (mkHsWrap wrap (HsVar (noLoc id)), rho) } inst_data_con con -- For data constructors, -- * Must perform the stupid-theta check -- * No need to deeply instantiate because type has all foralls at top = do { let wrap_id = dataConWrapId con (tvs, theta, rho) = tcSplitSigmaTy (idType wrap_id) ; (subst, tvs') <- tcInstTyVars tvs ; let tys' = mkTyVarTys tvs' theta' = substTheta subst theta rho' = substTy subst rho ; wrap <- instCall orig tys' theta' ; addDataConStupidTheta con tys' ; return (mkHsWrap wrap (HsVar (noLoc wrap_id)), rho') } check_naughty id | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl) | otherwise = return () {- Note [Adding the implicit parameter to 'assert'] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The typechecker transforms (assert e1 e2) to (assertError e1 e2). This isn't really the Right Thing because there's no way to "undo" if you want to see the original source code in the typechecker output. We'll have fix this in due course, when we care more about being able to reconstruct the exact original program. Note [tagToEnum#] ~~~~~~~~~~~~~~~~~ Nasty check to ensure that tagToEnum# is applied to a type that is an enumeration TyCon. Unification may refine the type later, but this check won't see that, alas. It's crude, because it relies on our knowing *now* that the type is ok, which in turn relies on the eager-unification part of the type checker pushing enough information here. In theory the Right Thing to do is to have a new form of constraint but I definitely cannot face that! And it works ok as-is. Here's are two cases that should fail f :: forall a. a f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable g :: Int g = tagToEnum# 0 -- Int is not an enumeration When data type families are involved it's a bit more complicated. data family F a data instance F [Int] = A | B | C Then we want to generate something like tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int] Usually that coercion is hidden inside the wrappers for constructors of F [Int] but here we have to do it explicitly. It's all grotesquely complicated. -} tcSeq :: SrcSpan -> Name -> LHsExpr Name -> LHsExpr Name -> TcRhoType -> TcM (HsExpr TcId) -- (seq e1 e2) :: res_ty -- We need a special typing rule because res_ty can be unboxed -- See Note [Typing rule for seq] tcSeq loc fun_name arg1 arg2 res_ty = do { fun <- tcLookupId fun_name ; (arg1', arg1_ty) <- tcInfer (tcMonoExpr arg1) ; arg2' <- tcMonoExpr arg2 res_ty ; let fun' = L loc (HsWrap ty_args (HsVar (L loc fun))) ty_args = WpTyApp res_ty <.> WpTyApp arg1_ty ; return (HsApp (L loc (HsApp fun' arg1')) arg2') } tcTagToEnum :: SrcSpan -> Name -> LHsExpr Name -> TcRhoType -> TcM (HsExpr TcId) -- tagToEnum# :: forall a. Int# -> a -- See Note [tagToEnum#] Urgh! tcTagToEnum loc fun_name arg res_ty = do { fun <- tcLookupId fun_name ; ty' <- zonkTcType res_ty -- Check that the type is algebraic ; let mb_tc_app = tcSplitTyConApp_maybe ty' Just (tc, tc_args) = mb_tc_app ; checkTc (isJust mb_tc_app) (mk_error ty' doc1) -- Look through any type family ; fam_envs <- tcGetFamInstEnvs ; let (rep_tc, rep_args, coi) = tcLookupDataFamInst fam_envs tc tc_args -- coi :: tc tc_args ~R rep_tc rep_args ; checkTc (isEnumerationTyCon rep_tc) (mk_error ty' doc2) ; arg' <- tcMonoExpr arg intPrimTy ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar (L loc fun))) rep_ty = mkTyConApp rep_tc rep_args ; return (mkHsWrapCoR (mkTcSymCo $ TcCoercion coi) $ HsApp fun' arg') } -- coi is a Representational coercion where doc1 = vcat [ ptext (sLit "Specify the type by giving a type signature") , ptext (sLit "e.g. (tagToEnum# x) :: Bool") ] doc2 = ptext (sLit "Result type must be an enumeration type") mk_error :: TcType -> SDoc -> SDoc mk_error ty what = hang (ptext (sLit "Bad call to tagToEnum#") <+> ptext (sLit "at type") <+> ppr ty) 2 what {- ************************************************************************ * * Template Haskell checks * * ************************************************************************ -} checkThLocalId :: Id -> TcM () checkThLocalId id = do { mb_local_use <- getStageAndBindLevel (idName id) ; case mb_local_use of Just (top_lvl, bind_lvl, use_stage) | thLevel use_stage > bind_lvl , isNotTopLevel top_lvl -> checkCrossStageLifting id use_stage _ -> return () -- Not a locally-bound thing, or -- no cross-stage link } -------------------------------------- checkCrossStageLifting :: Id -> ThStage -> TcM () -- If we are inside typed brackets, and (use_lvl > bind_lvl) -- we must check whether there's a cross-stage lift to do -- Examples \x -> [|| x ||] -- [|| map ||] -- There is no error-checking to do, because the renamer did that -- -- This is similar to checkCrossStageLifting in RnSplice, but -- this code is applied to *typed* brackets. checkCrossStageLifting id (Brack _ (TcPending ps_var lie_var)) = -- Nested identifiers, such as 'x' in -- E.g. \x -> [|| h x ||] -- We must behave as if the reference to x was -- h $(lift x) -- We use 'x' itself as the splice proxy, used by -- the desugarer to stitch it all back together. -- If 'x' occurs many times we may get many identical -- bindings of the same splice proxy, but that doesn't -- matter, although it's a mite untidy. do { let id_ty = idType id ; checkTc (isTauTy id_ty) (polySpliceErr id) -- If x is polymorphic, its occurrence sites might -- have different instantiations, so we can't use plain -- 'x' as the splice proxy name. I don't know how to -- solve this, and it's probably unimportant, so I'm -- just going to flag an error for now ; lift <- if isStringTy id_ty then do { sid <- tcLookupId THNames.liftStringName -- See Note [Lifting strings] ; return (HsVar (noLoc sid)) } else setConstraintVar lie_var $ -- Put the 'lift' constraint into the right LIE newMethodFromName (OccurrenceOf (idName id)) THNames.liftName id_ty -- Update the pending splices ; ps <- readMutVar ps_var ; let pending_splice = PendingTcSplice (idName id) (nlHsApp (noLoc lift) (nlHsVar id)) ; writeMutVar ps_var (pending_splice : ps) ; return () } checkCrossStageLifting _ _ = return () polySpliceErr :: Id -> SDoc polySpliceErr id = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id) {- Note [Lifting strings] ~~~~~~~~~~~~~~~~~~~~~~ If we see $(... [| s |] ...) where s::String, we don't want to generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc. So this conditional short-circuits the lifting mechanism to generate (liftString "xy") in that case. I didn't want to use overlapping instances for the Lift class in TH.Syntax, because that can lead to overlapping-instance errors in a polymorphic situation. If this check fails (which isn't impossible) we get another chance; see Note [Converting strings] in Convert.hs Local record selectors ~~~~~~~~~~~~~~~~~~~~~~ Record selectors for TyCons in this module are ordinary local bindings, which show up as ATcIds rather than AGlobals. So we need to check for naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds. ************************************************************************ * * \subsection{Record bindings} * * ************************************************************************ -} getFixedTyVars :: [FieldLabelString] -> [TyVar] -> [ConLike] -> TyVarSet -- These tyvars must not change across the updates getFixedTyVars upd_fld_occs univ_tvs cons = mkVarSet [tv1 | con <- cons , let (u_tvs, _, eqspec, prov_theta , req_theta, arg_tys, _) = conLikeFullSig con theta = eqSpecPreds eqspec ++ prov_theta ++ req_theta flds = conLikeFieldLabels con fixed_tvs = exactTyVarsOfTypes fixed_tys -- fixed_tys: See Note [Type of a record update] `unionVarSet` tyVarsOfTypes theta -- Universally-quantified tyvars that -- appear in any of the *implicit* -- arguments to the constructor are fixed -- See Note [Implict type sharing] fixed_tys = [ty | (fl, ty) <- zip flds arg_tys , not (flLabel fl `elem` upd_fld_occs)] , (tv1,tv) <- univ_tvs `zip` u_tvs , tv `elemVarSet` fixed_tvs ] {- Note [Disambiguating record fields] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When the -XDuplicateRecordFields extension is used, and the renamer encounters a record selector or update that it cannot immediately disambiguate (because it involves fields that belong to multiple datatypes), it will defer resolution of the ambiguity to the typechecker. In this case, the `Ambiguous` constructor of `AmbiguousFieldOcc` is used. Consider the following definitions: data S = MkS { foo :: Int } data T = MkT { foo :: Int, bar :: Int } data U = MkU { bar :: Int, baz :: Int } When the renamer sees `foo` as a selector or an update, it will not know which parent datatype is in use. For selectors, there are two possible ways to disambiguate: 1. Check if the pushed-in type is a function whose domain is a datatype, for example: f s = (foo :: S -> Int) s g :: T -> Int g = foo This is checked by `tcCheckRecSelId` when checking `HsRecFld foo`. 2. Check if the selector is applied to an argument that has a type signature, for example: h = foo (s :: S) This is checked by `tcApp`. Updates are slightly more complex. The `disambiguateRecordBinds` function tries to determine the parent datatype in three ways: 1. Check for types that have all the fields being updated. For example: f x = x { foo = 3, bar = 2 } Here `f` must be updating `T` because neither `S` nor `U` have both fields. This may also discover that no possible type exists. For example the following will be rejected: f' x = x { foo = 3, baz = 3 } 2. Use the type being pushed in, if it is already a TyConApp. The following are valid updates to `T`: g :: T -> T g x = x { foo = 3 } g' x = x { foo = 3 } :: T 3. Use the type signature of the record expression, if it exists and is a TyConApp. Thus this is valid update to `T`: h x = (x :: T) { foo = 3 } Note that we do not look up the types of variables being updated, and no constraint-solving is performed, so for example the following will be rejected as ambiguous: let bad (s :: S) = foo s let r :: T r = blah in r { foo = 3 } \r. (r { foo = 3 }, r :: T ) We could add further tests, of a more heuristic nature. For example, rather than looking for an explicit signature, we could try to infer the type of the argument to a selector or the record expression being updated, in case we are lucky enough to get a TyConApp straight away. However, it might be hard for programmers to predict whether a particular update is sufficiently obvious for the signature to be omitted. Moreover, this might change the behaviour of typechecker in non-obvious ways. See also Note [HsRecField and HsRecUpdField] in HsPat. -} -- Given a RdrName that refers to multiple record fields, and the type -- of its argument, try to determine the name of the selector that is -- meant. disambiguateSelector :: RdrName -> Type -> RnM Name disambiguateSelector rdr parent_type = do { fam_inst_envs <- tcGetFamInstEnvs ; case tyConOf fam_inst_envs parent_type of Nothing -> ambiguousSelector rdr Just p -> do { xs <- lookupParents rdr ; let parent = RecSelData p ; case lookup parent xs of Just gre -> do { addUsedGRE True gre ; return (gre_name gre) } Nothing -> failWithTc (fieldNotInType parent rdr) } } -- This field name really is ambiguous, so add a suitable "ambiguous -- occurrence" error, then give up. ambiguousSelector :: RdrName -> RnM a ambiguousSelector rdr = do { env <- getGlobalRdrEnv ; let gres = lookupGRE_RdrName rdr env ; setErrCtxt [] $ addNameClashErrRn rdr gres ; failM } -- Disambiguate the fields in a record update. -- See Note [Disambiguating record fields] disambiguateRecordBinds :: LHsExpr Name -> TcType -> [LHsRecUpdField Name] -> Type -> TcM [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)] disambiguateRecordBinds record_expr record_tau rbnds res_ty -- Are all the fields unambiguous? = case mapM isUnambiguous rbnds of -- If so, just skip to looking up the Ids -- Always the case if DuplicateRecordFields is off Just rbnds' -> mapM lookupSelector rbnds' Nothing -> -- If not, try to identify a single parent do { fam_inst_envs <- tcGetFamInstEnvs -- Look up the possible parents for each field ; rbnds_with_parents <- getUpdFieldsParents ; let possible_parents = map (map fst . snd) rbnds_with_parents -- Identify a single parent ; p <- identifyParent fam_inst_envs possible_parents -- Pick the right selector with that parent for each field ; checkNoErrs $ mapM (pickParent p) rbnds_with_parents } where -- Extract the selector name of a field update if it is unambiguous isUnambiguous :: LHsRecUpdField Name -> Maybe (LHsRecUpdField Name, Name) isUnambiguous x = case unLoc (hsRecFieldLbl (unLoc x)) of Unambiguous _ sel_name -> Just (x, sel_name) Ambiguous{} -> Nothing -- Look up the possible parents and selector GREs for each field getUpdFieldsParents :: TcM [(LHsRecUpdField Name , [(RecSelParent, GlobalRdrElt)])] getUpdFieldsParents = fmap (zip rbnds) $ mapM (lookupParents . unLoc . hsRecUpdFieldRdr . unLoc) rbnds -- Given a the lists of possible parents for each field, -- identify a single parent identifyParent :: FamInstEnvs -> [[RecSelParent]] -> TcM RecSelParent identifyParent fam_inst_envs possible_parents = case foldr1 intersect possible_parents of -- No parents for all fields: record update is ill-typed [] -> failWithTc (noPossibleParents rbnds) -- Exactly one datatype with all the fields: use that [p] -> return p -- Multiple possible parents: try harder to disambiguate -- Can we get a parent TyCon from the pushed-in type? _:_ | Just p <- tyConOf fam_inst_envs res_ty -> return (RecSelData p) -- Does the expression being updated have a type signature? -- If so, try to extract a parent TyCon from it | Just {} <- obviousSig (unLoc record_expr) , Just tc <- tyConOf fam_inst_envs record_tau -> return (RecSelData tc) -- Nothing else we can try... _ -> failWithTc badOverloadedUpdate -- Make a field unambiguous by choosing the given parent. -- Emits an error if the field cannot have that parent, -- e.g. if the user writes -- r { x = e } :: T -- where T does not have field x. pickParent :: RecSelParent -> (LHsRecUpdField Name, [(RecSelParent, GlobalRdrElt)]) -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)) pickParent p (upd, xs) = case lookup p xs of -- Phew! The parent is valid for this field. -- Previously ambiguous fields must be marked as -- used now that we know which one is meant, but -- unambiguous ones shouldn't be recorded again -- (giving duplicate deprecation warnings). Just gre -> do { unless (null (tail xs)) $ do let L loc _ = hsRecFieldLbl (unLoc upd) setSrcSpan loc $ addUsedGRE True gre ; lookupSelector (upd, gre_name gre) } -- The field doesn't belong to this parent, so report -- an error but keep going through all the fields Nothing -> do { addErrTc (fieldNotInType p (unLoc (hsRecUpdFieldRdr (unLoc upd)))) ; lookupSelector (upd, gre_name (snd (head xs))) } -- Given a (field update, selector name) pair, look up the -- selector to give a field update with an unambiguous Id lookupSelector :: (LHsRecUpdField Name, Name) -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)) lookupSelector (L l upd, n) = do { i <- tcLookupId n ; let L loc af = hsRecFieldLbl upd lbl = rdrNameAmbiguousFieldOcc af ; return $ L l upd { hsRecFieldLbl = L loc (Unambiguous lbl i) } } -- Extract the outermost TyCon of a type, if there is one; for -- data families this is the representation tycon (because that's -- where the fields live). Look inside sigma-types, so that -- tyConOf _ (forall a. Q => T a) = T tyConOf :: FamInstEnvs -> Type -> Maybe TyCon tyConOf fam_inst_envs ty0 = case tcSplitTyConApp_maybe ty of Just (tc, tys) -> Just (fstOf3 (tcLookupDataFamInst fam_inst_envs tc tys)) Nothing -> Nothing where (_, _, ty) = tcSplitSigmaTy ty0 -- For an ambiguous record field, find all the candidate record -- selectors (as GlobalRdrElts) and their parents. lookupParents :: RdrName -> RnM [(RecSelParent, GlobalRdrElt)] lookupParents rdr = do { env <- getGlobalRdrEnv ; let gres = lookupGRE_RdrName rdr env ; mapM lookupParent gres } where lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt) lookupParent gre = do { id <- tcLookupId (gre_name gre) ; if isRecordSelector id then return (recordSelectorTyCon id, gre) else failWithTc (notSelector (gre_name gre)) } -- A type signature on the argument of an ambiguous record selector or -- the record expression in an update must be "obvious", i.e. the -- outermost constructor ignoring parentheses. obviousSig :: HsExpr Name -> Maybe (LHsSigWcType Name) obviousSig (ExprWithTySig _ ty) = Just ty obviousSig (HsPar p) = obviousSig (unLoc p) obviousSig _ = Nothing {- Game plan for record bindings ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1. Find the TyCon for the bindings, from the first field label. 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty. For each binding field = value 3. Instantiate the field type (from the field label) using the type envt from step 2. 4 Type check the value using tcArg, passing the field type as the expected argument type. This extends OK when the field types are universally quantified. -} tcRecordBinds :: ConLike -> [TcType] -- Expected type for each field -> HsRecordBinds Name -> TcM (HsRecordBinds TcId) tcRecordBinds con_like arg_tys (HsRecFields rbinds dd) = do { mb_binds <- mapM do_bind rbinds ; return (HsRecFields (catMaybes mb_binds) dd) } where fields = map flLabel $ conLikeFieldLabels con_like flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys do_bind :: LHsRecField Name (LHsExpr Name) -> TcM (Maybe (LHsRecField TcId (LHsExpr TcId))) do_bind (L l fld@(HsRecField { hsRecFieldLbl = f , hsRecFieldArg = rhs })) = do { mb <- tcRecordField con_like flds_w_tys f rhs ; case mb of Nothing -> return Nothing Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = f' , hsRecFieldArg = rhs' }))) } tcRecordUpd :: ConLike -> [TcType] -- Expected type for each field -> [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)] -> TcM [LHsRecUpdField TcId] tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds where flds_w_tys = zipEqual "tcRecordUpd" (map flLabel $ conLikeFieldLabels con_like) arg_tys do_bind :: LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name) -> TcM (Maybe (LHsRecUpdField TcId)) do_bind (L l fld@(HsRecField { hsRecFieldLbl = L loc af , hsRecFieldArg = rhs })) = do { let lbl = rdrNameAmbiguousFieldOcc af sel_id = selectorAmbiguousFieldOcc af f = L loc (FieldOcc lbl (idName sel_id)) ; mb <- tcRecordField con_like flds_w_tys f rhs ; case mb of Nothing -> return Nothing Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = L loc (Unambiguous lbl (selectorFieldOcc (unLoc f'))) , hsRecFieldArg = rhs' }))) } tcRecordField :: ConLike -> Assoc FieldLabelString Type -> LFieldOcc Name -> LHsExpr Name -> TcM (Maybe (LFieldOcc Id, LHsExpr Id)) tcRecordField con_like flds_w_tys (L loc (FieldOcc lbl sel_name)) rhs | Just field_ty <- assocMaybe flds_w_tys field_lbl = addErrCtxt (fieldCtxt field_lbl) $ do { rhs' <- tcPolyExprNC rhs field_ty ; let field_id = mkUserLocal (nameOccName sel_name) (nameUnique sel_name) field_ty loc -- Yuk: the field_id has the *unique* of the selector Id -- (so we can find it easily) -- but is a LocalId with the appropriate type of the RHS -- (so the desugarer knows the type of local binder to make) ; return (Just (L loc (FieldOcc lbl field_id), rhs')) } | otherwise = do { addErrTc (badFieldCon con_like field_lbl) ; return Nothing } where field_lbl = occNameFS $ rdrNameOcc lbl checkMissingFields :: ConLike -> HsRecordBinds Name -> TcM () checkMissingFields con_like rbinds | null field_labels -- Not declared as a record; -- But C{} is still valid if no strict fields = if any isBanged field_strs then -- Illegal if any arg is strict addErrTc (missingStrictFields con_like []) else return () | otherwise = do -- A record unless (null missing_s_fields) (addErrTc (missingStrictFields con_like missing_s_fields)) warn <- woptM Opt_WarnMissingFields unless (not (warn && notNull missing_ns_fields)) (warnTc True (missingFields con_like missing_ns_fields)) where missing_s_fields = [ flLabel fl | (fl, str) <- field_info, isBanged str, not (fl `elemField` field_names_used) ] missing_ns_fields = [ flLabel fl | (fl, str) <- field_info, not (isBanged str), not (fl `elemField` field_names_used) ] field_names_used = hsRecFields rbinds field_labels = conLikeFieldLabels con_like field_info = zipEqual "missingFields" field_labels field_strs field_strs = conLikeImplBangs con_like fl `elemField` flds = any (\ fl' -> flSelector fl == fl') flds {- ************************************************************************ * * \subsection{Errors and contexts} * * ************************************************************************ Boring and alphabetical: -} addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a addExprErrCtxt expr = addErrCtxt (exprCtxt expr) exprCtxt :: LHsExpr Name -> SDoc exprCtxt expr = hang (ptext (sLit "In the expression:")) 2 (ppr expr) fieldCtxt :: FieldLabelString -> SDoc fieldCtxt field_name = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record") funAppCtxt :: LHsExpr Name -> LHsExpr Name -> Int -> SDoc funAppCtxt fun arg arg_no = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"), quotes (ppr fun) <> text ", namely"]) 2 (quotes (ppr arg)) funResCtxt :: Bool -- There is at least one argument -> HsExpr Name -> TcType -> TcType -> TidyEnv -> TcM (TidyEnv, MsgDoc) -- When we have a mis-match in the return type of a function -- try to give a helpful message about too many/few arguments -- -- Used for naked variables too; but with has_args = False funResCtxt has_args fun fun_res_ty env_ty tidy_env = do { fun_res' <- zonkTcType fun_res_ty ; env' <- zonkTcType env_ty ; let (args_fun, res_fun) = tcSplitFunTys fun_res' (args_env, res_env) = tcSplitFunTys env' n_fun = length args_fun n_env = length args_env info | n_fun == n_env = Outputable.empty | n_fun > n_env , not_fun res_env = ptext (sLit "Probable cause:") <+> quotes (ppr fun) <+> ptext (sLit "is applied to too few arguments") | has_args , not_fun res_fun = ptext (sLit "Possible cause:") <+> quotes (ppr fun) <+> ptext (sLit "is applied to too many arguments") | otherwise = Outputable.empty -- Never suggest that a naked variable is -- applied to too many args! ; return (tidy_env, info) } where not_fun ty -- ty is definitely not an arrow type, -- and cannot conceivably become one = case tcSplitTyConApp_maybe ty of Just (tc, _) -> isAlgTyCon tc Nothing -> False badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc badFieldTypes prs = hang (ptext (sLit "Record update for insufficiently polymorphic field") <> plural prs <> colon) 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ]) badFieldsUpd :: [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)] -- Field names that don't belong to a single datacon -> [ConLike] -- Data cons of the type which the first field name belongs to -> SDoc badFieldsUpd rbinds data_cons = hang (ptext (sLit "No constructor has all these fields:")) 2 (pprQuotedList conflictingFields) -- See Note [Finding the conflicting fields] where -- A (preferably small) set of fields such that no constructor contains -- all of them. See Note [Finding the conflicting fields] conflictingFields = case nonMembers of -- nonMember belongs to a different type. (nonMember, _) : _ -> [aMember, nonMember] [] -> let -- All of rbinds belong to one type. In this case, repeatedly add -- a field to the set until no constructor contains the set. -- Each field, together with a list indicating which constructors -- have all the fields so far. growingSets :: [(FieldLabelString, [Bool])] growingSets = scanl1 combine membership combine (_, setMem) (field, fldMem) = (field, zipWith (&&) setMem fldMem) in -- Fields that don't change the membership status of the set -- are redundant and can be dropped. map (fst . head) $ groupBy ((==) `on` snd) growingSets aMember = ASSERT( not (null members) ) fst (head members) (members, nonMembers) = partition (or . snd) membership -- For each field, which constructors contain the field? membership :: [(FieldLabelString, [Bool])] membership = sortMembership $ map (\fld -> (fld, map (Set.member fld) fieldLabelSets)) $ map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds fieldLabelSets :: [Set.Set FieldLabelString] fieldLabelSets = map (Set.fromList . map flLabel . conLikeFieldLabels) data_cons -- Sort in order of increasing number of True, so that a smaller -- conflicting set can be found. sortMembership = map snd . sortBy (compare `on` fst) . map (\ item@(_, membershipRow) -> (countTrue membershipRow, item)) countTrue = length . filter id {- Note [Finding the conflicting fields] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose we have data A = A {a0, a1 :: Int} | B {b0, b1 :: Int} and we see a record update x { a0 = 3, a1 = 2, b0 = 4, b1 = 5 } Then we'd like to find the smallest subset of fields that no constructor has all of. Here, say, {a0,b0}, or {a0,b1}, etc. We don't really want to report that no constructor has all of {a0,a1,b0,b1}, because when there are hundreds of fields it's hard to see what was really wrong. We may need more than two fields, though; eg data T = A { x,y :: Int, v::Int } | B { y,z :: Int, v::Int } | C { z,x :: Int, v::Int } with update r { x=e1, y=e2, z=e3 }, we Finding the smallest subset is hard, so the code here makes a decent stab, no more. See Trac #7989. -} naughtyRecordSel :: RdrName -> SDoc naughtyRecordSel sel_id = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+> ptext (sLit "as a function due to escaped type variables") $$ ptext (sLit "Probable fix: use pattern-matching syntax instead") notSelector :: Name -> SDoc notSelector field = hsep [quotes (ppr field), ptext (sLit "is not a record selector")] mixedSelectors :: [Id] -> [Id] -> SDoc mixedSelectors data_sels@(dc_rep_id:_) pat_syn_sels@(ps_rep_id:_) = ptext (sLit "Cannot use a mixture of pattern synonym and record selectors") $$ ptext (sLit "Record selectors defined by") <+> quotes (ppr (tyConName rep_dc)) <> text ":" <+> pprWithCommas ppr data_sels $$ ptext (sLit "Pattern synonym selectors defined by") <+> quotes (ppr (patSynName rep_ps)) <> text ":" <+> pprWithCommas ppr pat_syn_sels where RecSelPatSyn rep_ps = recordSelectorTyCon ps_rep_id RecSelData rep_dc = recordSelectorTyCon dc_rep_id mixedSelectors _ _ = panic "TcExpr: mixedSelectors emptylists" missingStrictFields :: ConLike -> [FieldLabelString] -> SDoc missingStrictFields con fields = header <> rest where rest | null fields = Outputable.empty -- Happens for non-record constructors -- with strict fields | otherwise = colon <+> pprWithCommas ppr fields header = ptext (sLit "Constructor") <+> quotes (ppr con) <+> ptext (sLit "does not have the required strict field(s)") missingFields :: ConLike -> [FieldLabelString] -> SDoc missingFields con fields = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:") <+> pprWithCommas ppr fields -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args)) noPossibleParents :: [LHsRecUpdField Name] -> SDoc noPossibleParents rbinds = hang (ptext (sLit "No type has all these fields:")) 2 (pprQuotedList fields) where fields = map (hsRecFieldLbl . unLoc) rbinds badOverloadedUpdate :: SDoc badOverloadedUpdate = ptext (sLit "Record update is ambiguous, and requires a type signature") fieldNotInType :: RecSelParent -> RdrName -> SDoc fieldNotInType p rdr = unknownSubordinateErr (ptext (sLit "field of type") <+> quotes (ppr p)) rdr