{-# LANGUAGE CPP #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TupleSections #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow] -- in module GHC.Hs.Extension {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-} {- % (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 -} module GHC.Tc.Gen.Expr ( tcCheckPolyExpr, tcCheckPolyExprNC, tcCheckMonoExpr, tcCheckMonoExprNC, tcMonoExpr, tcMonoExprNC, tcInferRho, tcInferRhoNC, tcExpr, tcSyntaxOp, tcSyntaxOpGen, SyntaxOpType(..), synKnownType, tcCheckId, addAmbiguousNameErr, getFixedTyVars ) where #include "GhclibHsVersions.h" import GHC.Prelude import {-# SOURCE #-} GHC.Tc.Gen.Splice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket ) import GHC.Hs import GHC.Rename.Utils import GHC.Tc.Utils.Zonk import GHC.Tc.Utils.Monad import GHC.Tc.Utils.Unify import GHC.Types.Basic import GHC.Types.SourceText import GHC.Core.Multiplicity import GHC.Core.UsageEnv import GHC.Tc.Utils.Instantiate import GHC.Tc.Gen.App import GHC.Tc.Gen.Head import GHC.Tc.Gen.Bind ( tcLocalBinds ) import GHC.Tc.Instance.Family ( tcGetFamInstEnvs ) import GHC.Core.FamInstEnv ( FamInstEnvs ) import GHC.Rename.Env ( addUsedGRE ) import GHC.Tc.Utils.Env import GHC.Tc.Gen.Arrow import GHC.Tc.Gen.Match import GHC.Tc.Gen.HsType import GHC.Tc.Gen.Pat import GHC.Tc.Utils.TcMType import GHC.Tc.Types.Origin import GHC.Tc.Utils.TcType as TcType import GHC.Types.Id import GHC.Types.Id.Info import GHC.Core.ConLike import GHC.Core.DataCon import GHC.Core.PatSyn import GHC.Types.Name import GHC.Types.Name.Env import GHC.Types.Name.Set import GHC.Types.Name.Reader import GHC.Core.TyCon import GHC.Core.Type import GHC.Tc.Types.Evidence import GHC.Types.Var.Set import GHC.Builtin.Types import GHC.Builtin.Names import GHC.Driver.Session import GHC.Types.SrcLoc import GHC.Utils.Misc import GHC.Data.List.SetOps import GHC.Data.Maybe import GHC.Utils.Outputable as Outputable import GHC.Utils.Panic import GHC.Data.FastString import Control.Monad import GHC.Core.Class(classTyCon) import GHC.Types.Unique.Set ( UniqSet, mkUniqSet, elementOfUniqSet, nonDetEltsUniqSet ) import qualified GHC.LanguageExtensions as LangExt import Data.Function import Data.List (partition, sortBy, groupBy, intersect) {- ************************************************************************ * * \subsection{Main wrappers} * * ************************************************************************ -} tcCheckPolyExpr, tcCheckPolyExprNC :: LHsExpr GhcRn -- Expression to type check -> TcSigmaType -- Expected type (could be a polytype) -> TcM (LHsExpr GhcTc) -- Generalised expr with expected type -- tcCheckPolyExpr 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 themselves. tcCheckPolyExpr expr res_ty = tcPolyExpr expr (mkCheckExpType res_ty) tcCheckPolyExprNC expr res_ty = tcPolyExprNC expr (mkCheckExpType res_ty) -- These versions take an ExpType tcPolyExpr, tcPolyExprNC :: LHsExpr GhcRn -> ExpSigmaType -> TcM (LHsExpr GhcTc) tcPolyExpr expr res_ty = addLExprCtxt expr $ do { traceTc "tcPolyExpr" (ppr res_ty) ; tcPolyExprNC expr res_ty } tcPolyExprNC (L loc expr) res_ty = set_loc_and_ctxt loc expr $ do { traceTc "tcPolyExprNC" (ppr res_ty) ; (wrap, expr') <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty -> tcExpr expr res_ty ; return $ L loc (mkHsWrap wrap expr') } where -- See Note [Rebindable syntax and HsExpansion), which describes -- the logic behind this location/context tweaking. set_loc_and_ctxt l e m = do inGenCode <- inGeneratedCode if inGenCode && not (isGeneratedSrcSpan l) then setSrcSpan l $ addExprCtxt e m else setSrcSpan l m --------------- tcCheckMonoExpr, tcCheckMonoExprNC :: LHsExpr GhcRn -- Expression to type check -> TcRhoType -- Expected type -- Definitely no foralls at the top -> TcM (LHsExpr GhcTc) tcCheckMonoExpr expr res_ty = tcMonoExpr expr (mkCheckExpType res_ty) tcCheckMonoExprNC expr res_ty = tcMonoExprNC expr (mkCheckExpType res_ty) tcMonoExpr, tcMonoExprNC :: LHsExpr GhcRn -- Expression to type check -> ExpRhoType -- Expected type -- Definitely no foralls at the top -> TcM (LHsExpr GhcTc) tcMonoExpr expr res_ty = addLExprCtxt expr $ tcMonoExprNC expr res_ty tcMonoExprNC (L loc expr) res_ty = setSrcSpan loc $ do { expr' <- tcExpr expr res_ty ; return (L loc expr') } --------------- tcInferRho, tcInferRhoNC :: LHsExpr GhcRn -> TcM (LHsExpr GhcTc, TcRhoType) -- Infer a *rho*-type. The return type is always instantiated. tcInferRho le = addLExprCtxt le $ tcInferRhoNC le tcInferRhoNC (L loc expr) = setSrcSpan loc $ do { (expr', rho) <- tcInfer (tcExpr expr) ; return (L loc expr', rho) } {- ********************************************************************* * * tcExpr: the main expression typechecker * * ********************************************************************* -} tcExpr :: HsExpr GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc) -- Use tcApp to typecheck appplications, which are treated specially -- by Quick Look. Specifically: -- - HsApp: value applications -- - HsTypeApp: type applications -- - HsVar: lone variables, to ensure that they can get an -- impredicative instantiation (via Quick Look -- driven by res_ty (in checking mode). -- - ExprWithTySig: (e :: type) -- See Note [Application chains and heads] in GHC.Tc.Gen.App tcExpr e@(HsVar {}) res_ty = tcApp e res_ty tcExpr e@(HsApp {}) res_ty = tcApp e res_ty tcExpr e@(HsAppType {}) res_ty = tcApp e res_ty tcExpr e@(ExprWithTySig {}) res_ty = tcApp e res_ty tcExpr e@(HsRecFld {}) res_ty = tcApp e res_ty -- Typecheck an occurrence of an unbound Id -- -- Some of these started life as a true expression hole "_". -- Others might simply be variables that accidentally have no binding site tcExpr e@(HsUnboundVar _ occ) res_ty = do { ty <- newOpenFlexiTyVarTy -- Allow Int# etc (#12531) ; name <- newSysName occ ; let ev = mkLocalId name Many ty ; emitNewExprHole occ ev ty ; tcEmitBindingUsage bottomUE -- Holes fit any usage environment -- (#18491) ; tcWrapResultO (UnboundOccurrenceOf occ) e (HsUnboundVar ev occ) ty res_ty } tcExpr e@(HsLit x lit) res_ty = do { let lit_ty = hsLitType lit ; tcWrapResult e (HsLit x (convertLit lit)) lit_ty res_ty } tcExpr (HsPar x expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty ; return (HsPar x expr') } tcExpr (HsPragE x prag expr) res_ty = do { expr' <- tcMonoExpr expr res_ty ; return (HsPragE x (tcExprPrag prag) expr') } tcExpr (HsOverLit x lit) res_ty = do { lit' <- newOverloadedLit lit res_ty ; return (HsOverLit x lit') } tcExpr (NegApp x expr neg_expr) res_ty = do { (expr', neg_expr') <- tcSyntaxOp NegateOrigin neg_expr [SynAny] res_ty $ \[arg_ty] [arg_mult] -> tcScalingUsage arg_mult $ tcCheckMonoExpr expr arg_ty ; return (NegApp x expr' neg_expr') } tcExpr e@(HsIPVar _ x) res_ty = do { {- 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 <- newOpenFlexiTyVarTy ; let ip_name = mkStrLitTy (hsIPNameFS x) ; ipClass <- tcLookupClass ipClassName ; ip_var <- emitWantedEvVar origin (mkClassPred ipClass [ip_name, ip_ty]) ; tcWrapResult e (fromDict ipClass ip_name ip_ty (HsVar noExtField (noLoc ip_var))) ip_ty res_ty } where -- Coerces a dictionary for `IP "x" t` into `t`. fromDict ipClass x ty = mkHsWrap $ mkWpCastR $ unwrapIP $ mkClassPred ipClass [x,ty] origin = IPOccOrigin x tcExpr e@(HsOverLabel _ mb_fromLabel l) res_ty = do { -- See Note [Type-checking overloaded labels] loc <- getSrcSpanM ; case mb_fromLabel of Just fromLabel -> tcExpr (applyFromLabel loc fromLabel) res_ty Nothing -> do { isLabelClass <- tcLookupClass isLabelClassName ; alpha <- newFlexiTyVarTy liftedTypeKind ; let pred = mkClassPred isLabelClass [lbl, alpha] ; loc <- getSrcSpanM ; var <- emitWantedEvVar origin pred ; tcWrapResult e (fromDict pred (HsVar noExtField (L loc var))) alpha res_ty } } where -- Coerces a dictionary for `IsLabel "x" t` into `t`, -- or `HasField "x" r a into `r -> a`. fromDict pred = mkHsWrap $ mkWpCastR $ unwrapIP pred origin = OverLabelOrigin l lbl = mkStrLitTy l applyFromLabel loc fromLabel = HsAppType noExtField (L loc (HsVar noExtField (L loc fromLabel))) (mkEmptyWildCardBndrs (L loc (HsTyLit noExtField (HsStrTy NoSourceText l)))) tcExpr (HsLam x match) res_ty = do { (wrap, match') <- tcMatchLambda herald match_ctxt match res_ty ; return (mkHsWrap wrap (HsLam x match')) } where match_ctxt = MC { mc_what = LambdaExpr, mc_body = tcBody } herald = sep [ text "The lambda expression" <+> quotes (pprSetDepth (PartWay 1) $ pprMatches match), -- The pprSetDepth makes the abstraction print briefly text "has"] tcExpr e@(HsLamCase x matches) res_ty = do { (wrap, matches') <- tcMatchLambda msg match_ctxt matches res_ty -- The laziness annotation is because we don't want to fail here -- if there are multiple arguments ; return (mkHsWrap wrap $ HsLamCase x matches') } where msg = sep [ text "The function" <+> quotes (ppr e) , text "requires"] match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody } {- Note [Type-checking overloaded labels] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Recall that we have module GHC.OverloadedLabels where class IsLabel (x :: Symbol) a where fromLabel :: a We translate `#foo` to `fromLabel @"foo"`, where we use * the in-scope `fromLabel` if `RebindableSyntax` is enabled; or if not * `GHC.OverloadedLabels.fromLabel`. In the `RebindableSyntax` case, the renamer will have filled in the first field of `HsOverLabel` with the `fromLabel` function to use, and we simply apply it to the appropriate visible type argument. In the `OverloadedLabels` case, 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 `alpha` (just like for implicit parameters). -} {- ************************************************************************ * * 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. -} tcExpr expr@(OpApp {}) res_ty = tcApp expr res_ty -- Right sections, equivalent to \ x -> x `op` expr, or -- \ x -> op x expr tcExpr expr@(SectionR x op arg2) res_ty = do { (op', op_ty) <- tcInferRhoNC op ; (wrap_fun, [Scaled arg1_mult arg1_ty, arg2_ty], op_res_ty) <- matchActualFunTysRho (mk_op_msg op) fn_orig (Just (ppr op)) 2 op_ty ; arg2' <- tcValArg (unLoc op) arg2 arg2_ty 2 ; let expr' = SectionR x (mkLHsWrap wrap_fun op') arg2' act_res_ty = mkVisFunTy arg1_mult arg1_ty op_res_ty ; tcWrapResultMono expr expr' act_res_ty res_ty } where fn_orig = lexprCtOrigin op -- It's important to use the origin of 'op', so that call-stacks -- come out right; they are driven by the OccurrenceOf CtOrigin -- See #13285 tcExpr expr@(SectionL x arg1 op) res_ty = do { (op', op_ty) <- tcInferRhoNC op ; dflags <- getDynFlags -- Note [Left sections] ; let n_reqd_args | xopt LangExt.PostfixOperators dflags = 1 | otherwise = 2 ; (wrap_fn, (arg1_ty:arg_tys), op_res_ty) <- matchActualFunTysRho (mk_op_msg op) fn_orig (Just (ppr op)) n_reqd_args op_ty ; arg1' <- tcValArg (unLoc op) arg1 arg1_ty 1 ; let expr' = SectionL x arg1' (mkLHsWrap wrap_fn op') act_res_ty = mkVisFunTys arg_tys op_res_ty ; tcWrapResultMono expr expr' act_res_ty res_ty } where fn_orig = lexprCtOrigin op -- It's important to use the origin of 'op', so that call-stacks -- come out right; they are driven by the OccurrenceOf CtOrigin -- See #13285 tcExpr expr@(ExplicitTuple x tup_args boxity) res_ty | all tupArgPresent tup_args = do { let arity = length tup_args tup_tc = tupleTyCon boxity arity -- NB: tupleTyCon doesn't flatten 1-tuples -- See Note [Don't flatten tuples from HsSyn] in GHC.Core.Make ; res_ty <- expTypeToType res_ty ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty -- Unboxed tuples have RuntimeRep vars, which we -- don't care about here -- See Note [Unboxed tuple RuntimeRep vars] in GHC.Core.TyCon ; let arg_tys' = case boxity of Unboxed -> drop arity arg_tys Boxed -> arg_tys ; tup_args1 <- tcTupArgs tup_args arg_tys' ; return $ mkHsWrapCo coi (ExplicitTuple x tup_args1 boxity) } | otherwise = -- The tup_args are a mixture of Present and Missing (for tuple sections) do { let arity = length tup_args ; arg_tys <- case boxity of { Boxed -> newFlexiTyVarTys arity liftedTypeKind ; Unboxed -> replicateM arity newOpenFlexiTyVarTy } -- Handle tuple sections where ; tup_args1 <- tcTupArgs tup_args arg_tys ; let expr' = ExplicitTuple x tup_args1 boxity missing_tys = [Scaled mult ty | (L _ (Missing (Scaled mult _)), ty) <- zip tup_args1 arg_tys] -- See Note [Linear fields generalization] in GHC.Tc.Gen.App act_res_ty = mkVisFunTys missing_tys (mkTupleTy1 boxity arg_tys) -- See Note [Don't flatten tuples from HsSyn] in GHC.Core.Make ; traceTc "ExplicitTuple" (ppr act_res_ty $$ ppr res_ty) ; tcWrapResultMono expr expr' act_res_ty res_ty } tcExpr (ExplicitSum _ alt arity expr) res_ty = do { let sum_tc = sumTyCon arity ; res_ty <- expTypeToType res_ty ; (coi, arg_tys) <- matchExpectedTyConApp sum_tc res_ty ; -- Drop levity vars, we don't care about them here let arg_tys' = drop arity arg_tys ; expr' <- tcCheckPolyExpr expr (arg_tys' `getNth` (alt - 1)) ; return $ mkHsWrapCo coi (ExplicitSum arg_tys' alt arity expr' ) } -- This will see the empty list only when -XOverloadedLists. -- See Note [Empty lists] in GHC.Hs.Expr. tcExpr (ExplicitList _ witness exprs) res_ty = case witness of Nothing -> do { res_ty <- expTypeToType res_ty ; (coi, elt_ty) <- matchExpectedListTy res_ty ; exprs' <- mapM (tc_elt elt_ty) exprs ; return $ mkHsWrapCo coi $ ExplicitList elt_ty Nothing exprs' } Just fln -> do { ((exprs', elt_ty), fln') <- tcSyntaxOp ListOrigin fln [synKnownType intTy, SynList] res_ty $ \ [elt_ty] [_int_mul, list_mul] -> -- We ignore _int_mul because the integer (first -- argument of fromListN) is statically known: it -- is desugared to a literal. Therefore there is -- no variable of which to scale the usage in that -- first argument, and `_int_mul` is completely -- free in this expression. do { exprs' <- mapM (tcScalingUsage list_mul . tc_elt elt_ty) exprs ; return (exprs', elt_ty) } ; return $ ExplicitList elt_ty (Just fln') exprs' } where tc_elt elt_ty expr = tcCheckPolyExpr expr elt_ty {- ************************************************************************ * * Let, case, if, do * * ************************************************************************ -} tcExpr (HsLet x (L l binds) expr) res_ty = do { (binds', expr') <- tcLocalBinds binds $ tcMonoExpr expr res_ty ; return (HsLet x (L l binds') expr') } tcExpr (HsCase x scrut matches) res_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 let mult = Many -- There is not yet syntax or inference mechanism for case -- expressions to be anything else than unrestricted. -- Typecheck the scrutinee. We use tcInferRho but tcInferSigma -- would also be possible (tcMatchesCase accepts sigma-types) -- Interesting litmus test: do these two behave the same? -- case id of {..} -- case (\v -> v) of {..} -- This design choice is discussed in #17790 ; (scrut', scrut_ty) <- tcScalingUsage mult $ tcInferRho scrut ; traceTc "HsCase" (ppr scrut_ty) ; matches' <- tcMatchesCase match_ctxt (Scaled mult scrut_ty) matches res_ty ; return (HsCase x scrut' matches') } where match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody } tcExpr (HsIf x pred b1 b2) res_ty = do { pred' <- tcCheckMonoExpr pred boolTy ; (u1,b1') <- tcCollectingUsage $ tcMonoExpr b1 res_ty ; (u2,b2') <- tcCollectingUsage $ tcMonoExpr b2 res_ty ; tcEmitBindingUsage (supUE u1 u2) ; return (HsIf x pred' b1' b2') } tcExpr (HsMultiIf _ alts) res_ty = do { alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts ; res_ty <- readExpType res_ty ; 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 x pat cmd) res_ty = do { (pat', cmd', coi) <- tcProc pat cmd res_ty ; return $ mkHsWrapCo coi (HsProc x pat' cmd') } -- Typechecks the static form and wraps it with a call to 'fromStaticPtr'. -- See Note [Grand plan for static forms] in GHC.Iface.Tidy.StaticPtrTable for an overview. -- To type check -- (static e) :: p a -- we want to check (e :: a), -- and wrap (static e) in a call to -- fromStaticPtr :: IsStatic p => StaticPtr a -> p a tcExpr (HsStatic fvs expr) res_ty = do { res_ty <- expTypeToType res_ty ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty ; (expr', lie) <- captureConstraints $ addErrCtxt (hang (text "In the body of a static form:") 2 (ppr expr) ) $ tcCheckPolyExprNC expr expr_ty -- Check that the free variables of the static form are closed. -- It's OK to use nonDetEltsUniqSet here as the only side effects of -- checkClosedInStaticForm are error messages. ; mapM_ checkClosedInStaticForm $ nonDetEltsUniqSet fvs -- 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 ; _ <- emitWantedEvVar StaticOrigin $ mkTyConApp (classTyCon typeableClass) [liftedTypeKind, expr_ty] -- Insert the constraints of the static form in a global list for later -- validation. ; emitStaticConstraints lie -- Wrap the static form with the 'fromStaticPtr' call. ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName [p_ty] ; let wrap = mkWpTyApps [expr_ty] ; loc <- getSrcSpanM ; return $ mkHsWrapCo co $ HsApp noExtField (L loc $ mkHsWrap wrap fromStaticPtr) (L loc (HsStatic fvs expr')) } {- ************************************************************************ * * Record construction and update * * ************************************************************************ -} tcExpr expr@(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_sigma) <- tcInferId con_name ; (con_wrap, con_tau) <- topInstantiate orig con_sigma -- a shallow instantiation should really be enough for -- a data constructor. ; let arity = conLikeArity con_like Right (arg_tys, actual_res_ty) = tcSplitFunTysN arity con_tau ; case conLikeWrapId_maybe con_like of { Nothing -> nonBidirectionalErr (conLikeName con_like) ; Just con_id -> do { rbinds' <- tcRecordBinds con_like (map scaledThing arg_tys) rbinds -- It is currently not possible for a record to have -- multiplicities. When they do, `tcRecordBinds` will take -- scaled types instead. Meanwhile, it's safe to take -- `scaledThing` above, as we know all the multiplicities are -- Many. ; let rcon_tc = RecordConTc { rcon_con_like = con_like , rcon_con_expr = mkHsWrap con_wrap con_expr } expr' = RecordCon { rcon_ext = rcon_tc , rcon_con_name = L loc con_id , rcon_flds = rbinds' } ; tcWrapResultMono expr expr' actual_res_ty res_ty } } } where orig = OccurrenceOf con_name {- 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 #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 GHC.Tc.TyCl), 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 expr@(RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty = ASSERT( notNull rbnds ) do { -- STEP -2: typecheck the record_expr, the record to be updated (record_expr', record_rho) <- tcScalingUsage Many $ tcInferRho record_expr -- Record update drops some of the content of the record (namely the -- content of the field being updated). As a consequence, unless the -- field being updated is unrestricted in the record, or we need an -- unrestricted record. Currently, we simply always require an -- unrestricted record. -- -- Consider the following example: -- -- data R a = R { self :: a } -- bad :: a ⊸ () -- bad x = let r = R x in case r { self = () } of { R x' -> x' } -- -- This should definitely *not* typecheck. -- STEP -1 See Note [Disambiguating record fields] in GHC.Tc.Gen.Head -- After this we know that rbinds is unambiguous ; rbinds <- disambiguateRecordBinds record_expr record_rho 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, scaled_con1_arg_tys, _) = conLikeFullSig con1 con1_arg_tys = map scaledThing scaled_con1_arg_tys -- We can safely drop the fields' multiplicities because -- they are currently always 1: there is no syntax for record -- fields with other multiplicities yet. This way we don't need -- to handle it in the rest of the function 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 (tyCoVarsOfType 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 :: TCvSubst -> (TyVar, TcType) -> TcM (TCvSubst, TcType) -- Deals with instantiation of kind variables -- c.f. GHC.Tc.Utils.TcMType.newMetaTyVars 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 { (subst', new_tv) <- newMetaTyVarX subst tv ; return (subst', mkTyVarTy new_tv) } ; (result_subst, con1_tvs') <- newMetaTyVars con1_tvs ; let result_inst_tys = mkTyVarTys con1_tvs' init_subst = mkEmptyTCvSubst (getTCvInScope result_subst) ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty init_subst (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_scrut <- unifyType (Just (ppr record_expr)) record_rho scrut_ty -- NB: normal unification is OK here (as opposed to subsumption), -- because for this to work out, both record_rho and scrut_ty have -- to be normal datatypes -- no contravariant stuff can go on -- STEP 5 -- Typecheck the bindings ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds -- STEP 6: Deal with the stupid theta ; let theta' = substThetaUnchecked 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' = substThetaUnchecked scrut_subst req_theta ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta' -- Phew! ; let upd_tc = RecordUpdTc { rupd_cons = relevant_cons , rupd_in_tys = scrut_inst_tys , rupd_out_tys = result_inst_tys , rupd_wrap = req_wrap } expr' = RecordUpd { rupd_expr = mkLHsWrap fam_co $ mkLHsWrapCo co_scrut record_expr' , rupd_flds = rbinds' , rupd_ext = upd_tc } ; tcWrapResult expr expr' rec_res_ty 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 {- ************************************************************************ * * Template Haskell * * ************************************************************************ -} -- HsSpliced is an annotation produced by 'GHC.Rename.Splice.rnSpliceExpr'. -- Here we get rid of it and add the finalizers to the global environment. -- -- See Note [Delaying modFinalizers in untyped splices] in GHC.Rename.Splice. tcExpr (HsSpliceE _ (HsSpliced _ mod_finalizers (HsSplicedExpr expr))) res_ty = do addModFinalizersWithLclEnv mod_finalizers tcExpr expr res_ty tcExpr (HsSpliceE _ splice) res_ty = tcSpliceExpr splice res_ty tcExpr e@(HsBracket _ brack) res_ty = tcTypedBracket e brack res_ty tcExpr e@(HsRnBracketOut _ brack ps) res_ty = tcUntypedBracket e brack ps res_ty {- ************************************************************************ * * Rebindable syntax * * ************************************************************************ -} -- See Note [Rebindable syntax and HsExpansion]. tcExpr (XExpr (HsExpanded a b)) t = fmap (XExpr . ExpansionExpr . HsExpanded a) $ setSrcSpan generatedSrcSpan (tcExpr b t) {- ************************************************************************ * * Catch-all * * ************************************************************************ -} tcExpr other _ = pprPanic "tcExpr" (ppr other) -- Include ArrForm, ArrApp, which shouldn't appear at all -- Also HsTcBracketOut, HsQuasiQuoteE {- ************************************************************************ * * Arithmetic sequences [a..b] etc * * ************************************************************************ -} tcArithSeq :: Maybe (SyntaxExpr GhcRn) -> ArithSeqInfo GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc) tcArithSeq witness seq@(From expr) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr' <-tcScalingUsage elt_mult $ tcCheckPolyExpr expr elt_ty ; enum_from <- newMethodFromName (ArithSeqOrigin seq) enumFromName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq enum_from wit' (From expr') } tcArithSeq witness seq@(FromThen expr1 expr2) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr1 elt_ty ; expr2' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr2 elt_ty ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq) enumFromThenName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq enum_from_then wit' (FromThen expr1' expr2') } tcArithSeq witness seq@(FromTo expr1 expr2) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr1 elt_ty ; expr2' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr2 elt_ty ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq) enumFromToName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq enum_from_to wit' (FromTo expr1' expr2') } tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr1 elt_ty ; expr2' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr2 elt_ty ; expr3' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr3 elt_ty ; eft <- newMethodFromName (ArithSeqOrigin seq) enumFromThenToName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq eft wit' (FromThenTo expr1' expr2' expr3') } ----------------- arithSeqEltType :: Maybe (SyntaxExpr GhcRn) -> ExpRhoType -> TcM (HsWrapper, Mult, TcType, Maybe (SyntaxExpr GhcTc)) arithSeqEltType Nothing res_ty = do { res_ty <- expTypeToType res_ty ; (coi, elt_ty) <- matchExpectedListTy res_ty ; return (mkWpCastN coi, One, elt_ty, Nothing) } arithSeqEltType (Just fl) res_ty = do { ((elt_mult, elt_ty), fl') <- tcSyntaxOp ListOrigin fl [SynList] res_ty $ \ [elt_ty] [elt_mult] -> return (elt_mult, elt_ty) ; return (idHsWrapper, elt_mult, elt_ty, Just fl') } ---------------- tcTupArgs :: [LHsTupArg GhcRn] -> [TcSigmaType] -> TcM [LHsTupArg GhcTc] tcTupArgs args tys = do MASSERT( equalLength args tys ) checkTupSize (length args) mapM go (args `zip` tys) where go (L l (Missing {}), arg_ty) = do { mult <- newFlexiTyVarTy multiplicityTy ; return (L l (Missing (Scaled mult arg_ty))) } go (L l (Present x expr), arg_ty) = do { expr' <- tcCheckPolyExpr expr arg_ty ; return (L l (Present x expr')) } --------------------------- -- See TcType.SyntaxOpType also for commentary tcSyntaxOp :: CtOrigin -> SyntaxExprRn -> [SyntaxOpType] -- ^ shape of syntax operator arguments -> ExpRhoType -- ^ overall result type -> ([TcSigmaType] -> [Mult] -> TcM a) -- ^ Type check any arguments, -- takes a type per hole and a -- multiplicity per arrow in -- the shape. -> TcM (a, SyntaxExprTc) -- ^ Typecheck a syntax operator -- The operator is a variable or a lambda at this stage (i.e. renamer -- output)t tcSyntaxOp orig expr arg_tys res_ty = tcSyntaxOpGen orig expr arg_tys (SynType res_ty) -- | Slightly more general version of 'tcSyntaxOp' that allows the caller -- to specify the shape of the result of the syntax operator tcSyntaxOpGen :: CtOrigin -> SyntaxExprRn -> [SyntaxOpType] -> SyntaxOpType -> ([TcSigmaType] -> [Mult] -> TcM a) -> TcM (a, SyntaxExprTc) tcSyntaxOpGen orig (SyntaxExprRn op) arg_tys res_ty thing_inside = do { (expr, sigma) <- tcInferAppHead op [] Nothing -- Nothing here might be improved, but all this -- code is scheduled for demolition anyway ; traceTc "tcSyntaxOpGen" (ppr op $$ ppr expr $$ ppr sigma) ; (result, expr_wrap, arg_wraps, res_wrap) <- tcSynArgA orig sigma arg_tys res_ty $ thing_inside ; traceTc "tcSyntaxOpGen" (ppr op $$ ppr expr $$ ppr sigma ) ; return (result, SyntaxExprTc { syn_expr = mkHsWrap expr_wrap expr , syn_arg_wraps = arg_wraps , syn_res_wrap = res_wrap }) } tcSyntaxOpGen _ NoSyntaxExprRn _ _ _ = panic "tcSyntaxOpGen" {- Note [tcSynArg] ~~~~~~~~~~~~~~~ Because of the rich structure of SyntaxOpType, we must do the contra-/covariant thing when working down arrows, to get the instantiation vs. skolemisation decisions correct (and, more obviously, the orientation of the HsWrappers). We thus have two tcSynArgs. -} -- works on "expected" types, skolemising where necessary -- See Note [tcSynArg] tcSynArgE :: CtOrigin -> TcSigmaType -> SyntaxOpType -- ^ shape it is expected to have -> ([TcSigmaType] -> [Mult] -> TcM a) -- ^ check the arguments -> TcM (a, HsWrapper) -- ^ returns a wrapper :: (type of right shape) "->" (type passed in) tcSynArgE orig sigma_ty syn_ty thing_inside = do { (skol_wrap, (result, ty_wrapper)) <- tcSkolemise GenSigCtxt sigma_ty $ \ rho_ty -> go rho_ty syn_ty ; return (result, skol_wrap <.> ty_wrapper) } where go rho_ty SynAny = do { result <- thing_inside [rho_ty] [] ; return (result, idHsWrapper) } go rho_ty SynRho -- same as SynAny, because we skolemise eagerly = do { result <- thing_inside [rho_ty] [] ; return (result, idHsWrapper) } go rho_ty SynList = do { (list_co, elt_ty) <- matchExpectedListTy rho_ty ; result <- thing_inside [elt_ty] [] ; return (result, mkWpCastN list_co) } go rho_ty (SynFun arg_shape res_shape) = do { ( match_wrapper -- :: (arg_ty -> res_ty) "->" rho_ty , ( ( (result, arg_ty, res_ty, op_mult) , res_wrapper ) -- :: res_ty_out "->" res_ty , arg_wrapper1, [], arg_wrapper2 ) ) -- :: arg_ty "->" arg_ty_out <- matchExpectedFunTys herald GenSigCtxt 1 (mkCheckExpType rho_ty) $ \ [arg_ty] res_ty -> do { arg_tc_ty <- expTypeToType (scaledThing arg_ty) ; res_tc_ty <- expTypeToType res_ty -- another nested arrow is too much for now, -- but I bet we'll never need this ; MASSERT2( case arg_shape of SynFun {} -> False; _ -> True , text "Too many nested arrows in SyntaxOpType" $$ pprCtOrigin orig ) ; let arg_mult = scaledMult arg_ty ; tcSynArgA orig arg_tc_ty [] arg_shape $ \ arg_results arg_res_mults -> tcSynArgE orig res_tc_ty res_shape $ \ res_results res_res_mults -> do { result <- thing_inside (arg_results ++ res_results) ([arg_mult] ++ arg_res_mults ++ res_res_mults) ; return (result, arg_tc_ty, res_tc_ty, arg_mult) }} ; return ( result , match_wrapper <.> mkWpFun (arg_wrapper2 <.> arg_wrapper1) res_wrapper (Scaled op_mult arg_ty) res_ty doc ) } where herald = text "This rebindable syntax expects a function with" doc = text "When checking a rebindable syntax operator arising from" <+> ppr orig go rho_ty (SynType the_ty) = do { wrap <- tcSubTypePat orig GenSigCtxt the_ty rho_ty ; result <- thing_inside [] [] ; return (result, wrap) } -- works on "actual" types, instantiating where necessary -- See Note [tcSynArg] tcSynArgA :: CtOrigin -> TcSigmaType -> [SyntaxOpType] -- ^ argument shapes -> SyntaxOpType -- ^ result shape -> ([TcSigmaType] -> [Mult] -> TcM a) -- ^ check the arguments -> TcM (a, HsWrapper, [HsWrapper], HsWrapper) -- ^ returns a wrapper to be applied to the original function, -- wrappers to be applied to arguments -- and a wrapper to be applied to the overall expression tcSynArgA orig sigma_ty arg_shapes res_shape thing_inside = do { (match_wrapper, arg_tys, res_ty) <- matchActualFunTysRho herald orig Nothing (length arg_shapes) sigma_ty -- match_wrapper :: sigma_ty "->" (arg_tys -> res_ty) ; ((result, res_wrapper), arg_wrappers) <- tc_syn_args_e (map scaledThing arg_tys) arg_shapes $ \ arg_results arg_res_mults -> tc_syn_arg res_ty res_shape $ \ res_results -> thing_inside (arg_results ++ res_results) (map scaledMult arg_tys ++ arg_res_mults) ; return (result, match_wrapper, arg_wrappers, res_wrapper) } where herald = text "This rebindable syntax expects a function with" tc_syn_args_e :: [TcSigmaType] -> [SyntaxOpType] -> ([TcSigmaType] -> [Mult] -> TcM a) -> TcM (a, [HsWrapper]) -- the wrappers are for arguments tc_syn_args_e (arg_ty : arg_tys) (arg_shape : arg_shapes) thing_inside = do { ((result, arg_wraps), arg_wrap) <- tcSynArgE orig arg_ty arg_shape $ \ arg1_results arg1_mults -> tc_syn_args_e arg_tys arg_shapes $ \ args_results args_mults -> thing_inside (arg1_results ++ args_results) (arg1_mults ++ args_mults) ; return (result, arg_wrap : arg_wraps) } tc_syn_args_e _ _ thing_inside = (, []) <$> thing_inside [] [] tc_syn_arg :: TcSigmaType -> SyntaxOpType -> ([TcSigmaType] -> TcM a) -> TcM (a, HsWrapper) -- the wrapper applies to the overall result tc_syn_arg res_ty SynAny thing_inside = do { result <- thing_inside [res_ty] ; return (result, idHsWrapper) } tc_syn_arg res_ty SynRho thing_inside = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty -- inst_wrap :: res_ty "->" rho_ty ; result <- thing_inside [rho_ty] ; return (result, inst_wrap) } tc_syn_arg res_ty SynList thing_inside = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty -- inst_wrap :: res_ty "->" rho_ty ; (list_co, elt_ty) <- matchExpectedListTy rho_ty -- list_co :: [elt_ty] ~N rho_ty ; result <- thing_inside [elt_ty] ; return (result, mkWpCastN (mkTcSymCo list_co) <.> inst_wrap) } tc_syn_arg _ (SynFun {}) _ = pprPanic "tcSynArgA hits a SynFun" (ppr orig) tc_syn_arg res_ty (SynType the_ty) thing_inside = do { wrap <- tcSubType orig GenSigCtxt res_ty the_ty ; result <- thing_inside [] ; return (result, wrap) } {- 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. -} {- ********************************************************************* * * 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 = exactTyCoVarsOfTypes (map scaledThing fixed_tys) -- fixed_tys: See Note [Type of a record update] `unionVarSet` tyCoVarsOfTypes theta -- Universally-quantified tyvars that -- appear in any of the *implicit* -- arguments to the constructor are fixed -- See Note [Implicit 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 ] -- Disambiguate the fields in a record update. -- See Note [Disambiguating record fields] in GHC.Tc.Gen.Head disambiguateRecordBinds :: LHsExpr GhcRn -> TcRhoType -> [LHsRecUpdField GhcRn] -> ExpRhoType -> TcM [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)] disambiguateRecordBinds record_expr record_rho 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 GhcRn -> Maybe (LHsRecUpdField GhcRn,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 GhcRn , [(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 <- tyConOfET 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_rho -> 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 GhcRn, [(RecSelParent, GlobalRdrElt)]) -> TcM (LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)) 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 GhcRn, Name) -> TcM (LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)) 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 i (L loc lbl)) } } {- 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 tcValArg, 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 GhcRn -> TcM (HsRecordBinds GhcTc) tcRecordBinds con_like arg_tys (HsRecFields rbinds dd) = do { mb_binds <- mapM do_bind rbinds ; return (HsRecFields (catMaybes mb_binds) dd) } where fields = map flSelector $ conLikeFieldLabels con_like flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys do_bind :: LHsRecField GhcRn (LHsExpr GhcRn) -> TcM (Maybe (LHsRecField GhcTc (LHsExpr GhcTc))) 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 GhcTc) (LHsExpr GhcRn)] -> TcM [LHsRecUpdField GhcTc] tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds where fields = map flSelector $ conLikeFieldLabels con_like flds_w_tys = zipEqual "tcRecordUpd" fields arg_tys do_bind :: LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn) -> TcM (Maybe (LHsRecUpdField GhcTc)) 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 (idName sel_id) (L loc lbl)) ; 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 (extFieldOcc (unLoc f')) (L loc lbl)) , hsRecFieldArg = rhs' }))) } tcRecordField :: ConLike -> Assoc Name Type -> LFieldOcc GhcRn -> LHsExpr GhcRn -> TcM (Maybe (LFieldOcc GhcTc, LHsExpr GhcTc)) tcRecordField con_like flds_w_tys (L loc (FieldOcc sel_name lbl)) rhs | Just field_ty <- assocMaybe flds_w_tys sel_name = addErrCtxt (fieldCtxt field_lbl) $ do { rhs' <- tcCheckPolyExprNC rhs field_ty ; let field_id = mkUserLocal (nameOccName sel_name) (nameUnique sel_name) Many 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 field_id lbl), rhs')) } | otherwise = do { addErrTc (badFieldCon con_like field_lbl) ; return Nothing } where field_lbl = occNameFS $ rdrNameOcc (unLoc lbl) checkMissingFields :: ConLike -> HsRecordBinds GhcRn -> 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 do warn <- woptM Opt_WarnMissingFields when (warn && notNull field_strs && null field_labels) (warnTc (Reason Opt_WarnMissingFields) True (missingFields con_like [])) | otherwise = do -- A record unless (null missing_s_fields) (addErrTc (missingStrictFields con_like missing_s_fields)) warn <- woptM Opt_WarnMissingFields when (warn && notNull missing_ns_fields) (warnTc (Reason Opt_WarnMissingFields) 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: -} fieldCtxt :: FieldLabelString -> SDoc fieldCtxt field_name = text "In the" <+> quotes (ppr field_name) <+> ptext (sLit "field of a record") mk_op_msg :: LHsExpr GhcRn -> SDoc mk_op_msg op = text "The operator" <+> quotes (ppr op) <+> text "takes" badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc badFieldTypes prs = hang (text "Record update for insufficiently polymorphic field" <> plural prs <> colon) 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ]) badFieldsUpd :: [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)] -- 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 (text "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 (fld `elementOfUniqSet`) fieldLabelSets)) $ map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds fieldLabelSets :: [UniqSet FieldLabelString] fieldLabelSets = map (mkUniqSet . 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 = count 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 #7989. -} 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") $$ text "Record selectors defined by" <+> quotes (ppr (tyConName rep_dc)) <> text ":" <+> pprWithCommas ppr data_sels $$ text "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 "GHC.Tc.Gen.Expr: 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 = text "Constructor" <+> quotes (ppr con) <+> text "does not have the required strict field(s)" missingFields :: ConLike -> [FieldLabelString] -> SDoc missingFields con fields = header <> rest where rest | null fields = Outputable.empty | otherwise = colon <+> pprWithCommas ppr fields header = text "Fields of" <+> quotes (ppr con) <+> text "not initialised" -- callCtxt fun args = text "In the call" <+> parens (ppr (foldl' mkHsApp fun args)) noPossibleParents :: [LHsRecUpdField GhcRn] -> SDoc noPossibleParents rbinds = hang (text "No type has all these fields:") 2 (pprQuotedList fields) where fields = map (hsRecFieldLbl . unLoc) rbinds badOverloadedUpdate :: SDoc badOverloadedUpdate = text "Record update is ambiguous, and requires a type signature" {- ************************************************************************ * * \subsection{Static Pointers} * * ************************************************************************ -} -- | A data type to describe why a variable is not closed. data NotClosedReason = NotLetBoundReason | NotTypeClosed VarSet | NotClosed Name NotClosedReason -- | Checks if the given name is closed and emits an error if not. -- -- See Note [Not-closed error messages]. checkClosedInStaticForm :: Name -> TcM () checkClosedInStaticForm name = do type_env <- getLclTypeEnv case checkClosed type_env name of Nothing -> return () Just reason -> addErrTc $ explain name reason where -- See Note [Checking closedness]. checkClosed :: TcTypeEnv -> Name -> Maybe NotClosedReason checkClosed type_env n = checkLoop type_env (unitNameSet n) n checkLoop :: TcTypeEnv -> NameSet -> Name -> Maybe NotClosedReason checkLoop type_env visited n = -- The @visited@ set is an accumulating parameter that contains the set of -- visited nodes, so we avoid repeating cycles in the traversal. case lookupNameEnv type_env n of Just (ATcId { tct_id = tcid, tct_info = info }) -> case info of ClosedLet -> Nothing NotLetBound -> Just NotLetBoundReason NonClosedLet fvs type_closed -> listToMaybe $ -- Look for a non-closed variable in fvs [ NotClosed n' reason | n' <- nameSetElemsStable fvs , not (elemNameSet n' visited) , Just reason <- [checkLoop type_env (extendNameSet visited n') n'] ] ++ if type_closed then [] else -- We consider non-let-bound variables easier to figure out than -- non-closed types, so we report non-closed types to the user -- only if we cannot spot the former. [ NotTypeClosed $ tyCoVarsOfType (idType tcid) ] -- The binding is closed. _ -> Nothing -- Converts a reason into a human-readable sentence. -- -- @explain name reason@ starts with -- -- " is used in a static form but it is not closed because it" -- -- and then follows a list of causes. For each id in the path, the text -- -- "uses which" -- -- is appended, yielding something like -- -- "uses which uses which uses which" -- -- until the end of the path is reached, which is reported as either -- -- "is not let-bound" -- -- when the final node is not let-bound, or -- -- "has a non-closed type because it contains the type variables: -- v1, v2, v3" -- -- when the final node has a non-closed type. -- explain :: Name -> NotClosedReason -> SDoc explain name reason = quotes (ppr name) <+> text "is used in a static form but it is not closed" <+> text "because it" $$ sep (causes reason) causes :: NotClosedReason -> [SDoc] causes NotLetBoundReason = [text "is not let-bound."] causes (NotTypeClosed vs) = [ text "has a non-closed type because it contains the" , text "type variables:" <+> pprVarSet vs (hsep . punctuate comma . map (quotes . ppr)) ] causes (NotClosed n reason) = let msg = text "uses" <+> quotes (ppr n) <+> text "which" in case reason of NotClosed _ _ -> msg : causes reason _ -> let (xs0, xs1) = splitAt 1 $ causes reason in fmap (msg <+>) xs0 ++ xs1 -- Note [Not-closed error messages] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- When variables in a static form are not closed, we go through the trouble -- of explaining why they aren't. -- -- Thus, the following program -- -- > {-# LANGUAGE StaticPointers #-} -- > module M where -- > -- > f x = static g -- > where -- > g = h -- > h = x -- -- produces the error -- -- 'g' is used in a static form but it is not closed because it -- uses 'h' which uses 'x' which is not let-bound. -- -- And a program like -- -- > {-# LANGUAGE StaticPointers #-} -- > module M where -- > -- > import Data.Typeable -- > import GHC.StaticPtr -- > -- > f :: Typeable a => a -> StaticPtr TypeRep -- > f x = const (static (g undefined)) (h x) -- > where -- > g = h -- > h = typeOf -- -- produces the error -- -- 'g' is used in a static form but it is not closed because it -- uses 'h' which has a non-closed type because it contains the -- type variables: 'a' -- -- Note [Checking closedness] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- @checkClosed@ checks if a binding is closed and returns a reason if it is -- not. -- -- The bindings define a graph where the nodes are ids, and there is an edge -- from @id1@ to @id2@ if the rhs of @id1@ contains @id2@ among its free -- variables. -- -- When @n@ is not closed, it has to exist in the graph some node reachable -- from @n@ that it is not a let-bound variable or that it has a non-closed -- type. Thus, the "reason" is a path from @n@ to this offending node. -- -- When @n@ is not closed, we traverse the graph reachable from @n@ to build -- the reason. --