-- (c) The University of Glasgow 2006 {-# LANGUAGE CPP, DeriveDataTypeable #-} {-# LANGUAGE LambdaCase #-} module GHC.Tc.Types.Evidence ( -- * HsWrapper HsWrapper(..), (<.>), mkWpTyApps, mkWpEvApps, mkWpEvVarApps, mkWpTyLams, mkWpLams, mkWpLet, mkWpCastN, mkWpCastR, collectHsWrapBinders, mkWpFun, idHsWrapper, isIdHsWrapper, pprHsWrapper, hsWrapDictBinders, -- * Evidence bindings TcEvBinds(..), EvBindsVar(..), EvBindMap(..), emptyEvBindMap, extendEvBinds, lookupEvBind, evBindMapBinds, foldEvBindMap, nonDetStrictFoldEvBindMap, filterEvBindMap, isEmptyEvBindMap, evBindMapToVarSet, varSetMinusEvBindMap, EvBind(..), emptyTcEvBinds, isEmptyTcEvBinds, mkGivenEvBind, mkWantedEvBind, evBindVar, isCoEvBindsVar, -- * EvTerm (already a CoreExpr) EvTerm(..), EvExpr, evId, evCoercion, evCast, evDFunApp, evDataConApp, evSelector, mkEvCast, evVarsOfTerm, mkEvScSelectors, evTypeable, findNeededEvVars, evTermCoercion, evTermCoercion_maybe, EvCallStack(..), EvTypeable(..), -- * HoleExprRef HoleExprRef(..), -- * TcCoercion TcCoercion, TcCoercionR, TcCoercionN, TcCoercionP, CoercionHole, TcMCoercion, TcMCoercionN, TcMCoercionR, Role(..), LeftOrRight(..), pickLR, mkTcReflCo, mkTcNomReflCo, mkTcRepReflCo, mkTcTyConAppCo, mkTcAppCo, mkTcFunCo, mkTcAxInstCo, mkTcUnbranchedAxInstCo, mkTcForAllCo, mkTcForAllCos, mkTcSymCo, mkTcSymMCo, mkTcTransCo, mkTcNthCo, mkTcLRCo, mkTcSubCo, maybeTcSymCo, maybeTcSubCo, tcDowngradeRole, mkTcAxiomRuleCo, mkTcGReflRightCo, mkTcGReflRightMCo, mkTcGReflLeftCo, mkTcGReflLeftMCo, mkTcPhantomCo, mkTcCoherenceLeftCo, mkTcCoherenceRightCo, mkTcKindCo, tcCoercionKind, mkTcCoVarCo, mkTcFamilyTyConAppCo, isTcReflCo, isTcReflexiveCo, tcCoercionRole, unwrapIP, wrapIP, -- * QuoteWrapper QuoteWrapper(..), applyQuoteWrapper, quoteWrapperTyVarTy ) where #include "GhclibHsVersions.h" import GHC.Prelude import GHC.Types.Unique.DFM import GHC.Types.Unique.FM import GHC.Types.Var import GHC.Core.Coercion.Axiom import GHC.Core.Coercion import GHC.Core.Ppr () -- Instance OutputableBndr TyVar import GHC.Tc.Utils.TcType import GHC.Core.Type import GHC.Core.TyCon import GHC.Core.DataCon ( DataCon, dataConWrapId ) import GHC.Builtin.Names import GHC.Types.Var.Env import GHC.Types.Var.Set import GHC.Core.Predicate import GHC.Types.Name import GHC.Data.Pair import GHC.Types.Basic import GHC.Core import GHC.Core.Class (Class, classSCSelId ) import GHC.Core.FVs ( exprSomeFreeVars ) import GHC.Utils.Misc import GHC.Utils.Panic import GHC.Utils.Outputable import GHC.Data.Bag import qualified Data.Data as Data import GHC.Types.SrcLoc import Data.IORef( IORef ) import GHC.Types.Unique.Set import GHC.Core.Multiplicity {- Note [TcCoercions] ~~~~~~~~~~~~~~~~~~ | TcCoercions are a hack used by the typechecker. Normally, Coercions have free variables of type (a ~# b): we call these CoVars. However, the type checker passes around equality evidence (boxed up) at type (a ~ b). An TcCoercion is simply a Coercion whose free variables have may be either boxed or unboxed. After we are done with typechecking the desugarer finds the boxed free variables, unboxes them, and creates a resulting real Coercion with kosher free variables. -} type TcCoercion = Coercion type TcCoercionN = CoercionN -- A Nominal coercion ~N type TcCoercionR = CoercionR -- A Representational coercion ~R type TcCoercionP = CoercionP -- a phantom coercion type TcMCoercion = MCoercion type TcMCoercionN = MCoercionN -- nominal type TcMCoercionR = MCoercionR -- representational mkTcReflCo :: Role -> TcType -> TcCoercion mkTcSymCo :: TcCoercion -> TcCoercion mkTcSymMCo :: TcMCoercion -> TcMCoercion mkTcTransCo :: TcCoercion -> TcCoercion -> TcCoercion mkTcNomReflCo :: TcType -> TcCoercionN mkTcRepReflCo :: TcType -> TcCoercionR mkTcTyConAppCo :: Role -> TyCon -> [TcCoercion] -> TcCoercion mkTcAppCo :: TcCoercion -> TcCoercionN -> TcCoercion mkTcFunCo :: Role -> TcCoercion -> TcCoercion -> TcCoercion -> TcCoercion mkTcAxInstCo :: Role -> CoAxiom br -> BranchIndex -> [TcType] -> [TcCoercion] -> TcCoercion mkTcUnbranchedAxInstCo :: CoAxiom Unbranched -> [TcType] -> [TcCoercion] -> TcCoercionR mkTcForAllCo :: TyVar -> TcCoercionN -> TcCoercion -> TcCoercion mkTcForAllCos :: [(TyVar, TcCoercionN)] -> TcCoercion -> TcCoercion mkTcNthCo :: Role -> Int -> TcCoercion -> TcCoercion mkTcLRCo :: LeftOrRight -> TcCoercion -> TcCoercion mkTcSubCo :: HasDebugCallStack => TcCoercionN -> TcCoercionR tcDowngradeRole :: Role -> Role -> TcCoercion -> TcCoercion mkTcAxiomRuleCo :: CoAxiomRule -> [TcCoercion] -> TcCoercionR mkTcGReflRightCo :: Role -> TcType -> TcCoercionN -> TcCoercion mkTcGReflRightMCo :: Role -> TcType -> TcMCoercionN -> TcCoercion mkTcGReflLeftCo :: Role -> TcType -> TcCoercionN -> TcCoercion mkTcGReflLeftMCo :: Role -> TcType -> TcMCoercionN -> TcCoercion mkTcCoherenceLeftCo :: Role -> TcType -> TcCoercionN -> TcCoercion -> TcCoercion mkTcCoherenceRightCo :: Role -> TcType -> TcCoercionN -> TcCoercion -> TcCoercion mkTcPhantomCo :: TcCoercionN -> TcType -> TcType -> TcCoercionP mkTcKindCo :: TcCoercion -> TcCoercionN mkTcCoVarCo :: CoVar -> TcCoercion mkTcFamilyTyConAppCo :: TyCon -> [TcCoercionN] -> TcCoercionN tcCoercionKind :: TcCoercion -> Pair TcType tcCoercionRole :: TcCoercion -> Role isTcReflCo :: TcCoercion -> Bool -- | This version does a slow check, calculating the related types and seeing -- if they are equal. isTcReflexiveCo :: TcCoercion -> Bool mkTcReflCo = mkReflCo mkTcSymCo = mkSymCo mkTcSymMCo = mkSymMCo mkTcTransCo = mkTransCo mkTcNomReflCo = mkNomReflCo mkTcRepReflCo = mkRepReflCo mkTcTyConAppCo = mkTyConAppCo mkTcAppCo = mkAppCo mkTcFunCo = mkFunCo mkTcAxInstCo = mkAxInstCo mkTcUnbranchedAxInstCo = mkUnbranchedAxInstCo Representational mkTcForAllCo = mkForAllCo mkTcForAllCos = mkForAllCos mkTcNthCo = mkNthCo mkTcLRCo = mkLRCo mkTcSubCo = mkSubCo tcDowngradeRole = downgradeRole mkTcAxiomRuleCo = mkAxiomRuleCo mkTcGReflRightCo = mkGReflRightCo mkTcGReflRightMCo = mkGReflRightMCo mkTcGReflLeftCo = mkGReflLeftCo mkTcGReflLeftMCo = mkGReflLeftMCo mkTcCoherenceLeftCo = mkCoherenceLeftCo mkTcCoherenceRightCo = mkCoherenceRightCo mkTcPhantomCo = mkPhantomCo mkTcKindCo = mkKindCo mkTcCoVarCo = mkCoVarCo mkTcFamilyTyConAppCo = mkFamilyTyConAppCo tcCoercionKind = coercionKind tcCoercionRole = coercionRole isTcReflCo = isReflCo isTcReflexiveCo = isReflexiveCo -- | If the EqRel is ReprEq, makes a SubCo; otherwise, does nothing. -- Note that the input coercion should always be nominal. maybeTcSubCo :: HasDebugCallStack => EqRel -> TcCoercionN -> TcCoercion maybeTcSubCo NomEq = id maybeTcSubCo ReprEq = mkTcSubCo -- | If a 'SwapFlag' is 'IsSwapped', flip the orientation of a coercion maybeTcSymCo :: SwapFlag -> TcCoercion -> TcCoercion maybeTcSymCo IsSwapped co = mkTcSymCo co maybeTcSymCo NotSwapped co = co {- %************************************************************************ %* * HsWrapper * * ************************************************************************ -} data HsWrapper = WpHole -- The identity coercion | WpCompose HsWrapper HsWrapper -- (wrap1 `WpCompose` wrap2)[e] = wrap1[ wrap2[ e ]] -- -- Hence (\a. []) `WpCompose` (\b. []) = (\a b. []) -- But ([] a) `WpCompose` ([] b) = ([] b a) | WpFun HsWrapper HsWrapper (Scaled TcType) SDoc -- (WpFun wrap1 wrap2 (w, t1))[e] = \(x:_w t1). wrap2[ e wrap1[x] ] -- So note that if wrap1 :: exp_arg <= act_arg -- wrap2 :: act_res <= exp_res -- then WpFun wrap1 wrap2 : (act_arg -> arg_res) <= (exp_arg -> exp_res) -- This isn't the same as for mkFunCo, but it has to be this way -- because we can't use 'sym' to flip around these HsWrappers -- The TcType is the "from" type of the first wrapper -- The SDoc explains the circumstances under which we have created this -- WpFun, in case we run afoul of levity polymorphism restrictions in -- the desugarer. See Note [Levity polymorphism checking] in GHC.HsToCore.Monad | WpCast TcCoercionR -- A cast: [] `cast` co -- Guaranteed not the identity coercion -- At role Representational -- Evidence abstraction and application -- (both dictionaries and coercions) | WpEvLam EvVar -- \d. [] the 'd' is an evidence variable | WpEvApp EvTerm -- [] d the 'd' is evidence for a constraint -- Kind and Type abstraction and application | WpTyLam TyVar -- \a. [] the 'a' is a type/kind variable (not coercion var) | WpTyApp KindOrType -- [] t the 't' is a type (not coercion) | WpLet TcEvBinds -- Non-empty (or possibly non-empty) evidence bindings, -- so that the identity coercion is always exactly WpHole | WpMultCoercion Coercion -- Require that a Coercion be reflexive; otherwise, -- error in the desugarer. See GHC.Tc.Utils.Unify -- Note [Wrapper returned from tcSubMult] -- Cannot derive Data instance because SDoc is not Data (it stores a function). -- So we do it manually: instance Data.Data HsWrapper where gfoldl _ z WpHole = z WpHole gfoldl k z (WpCompose a1 a2) = z WpCompose `k` a1 `k` a2 gfoldl k z (WpFun a1 a2 a3 _) = z wpFunEmpty `k` a1 `k` a2 `k` a3 gfoldl k z (WpCast a1) = z WpCast `k` a1 gfoldl k z (WpEvLam a1) = z WpEvLam `k` a1 gfoldl k z (WpEvApp a1) = z WpEvApp `k` a1 gfoldl k z (WpTyLam a1) = z WpTyLam `k` a1 gfoldl k z (WpTyApp a1) = z WpTyApp `k` a1 gfoldl k z (WpLet a1) = z WpLet `k` a1 gfoldl k z (WpMultCoercion a1) = z WpMultCoercion `k` a1 gunfold k z c = case Data.constrIndex c of 1 -> z WpHole 2 -> k (k (z WpCompose)) 3 -> k (k (k (z wpFunEmpty))) 4 -> k (z WpCast) 5 -> k (z WpEvLam) 6 -> k (z WpEvApp) 7 -> k (z WpTyLam) 8 -> k (z WpTyApp) 9 -> k (z WpLet) _ -> k (z WpMultCoercion) toConstr WpHole = wpHole_constr toConstr (WpCompose _ _) = wpCompose_constr toConstr (WpFun _ _ _ _) = wpFun_constr toConstr (WpCast _) = wpCast_constr toConstr (WpEvLam _) = wpEvLam_constr toConstr (WpEvApp _) = wpEvApp_constr toConstr (WpTyLam _) = wpTyLam_constr toConstr (WpTyApp _) = wpTyApp_constr toConstr (WpLet _) = wpLet_constr toConstr (WpMultCoercion _) = wpMultCoercion_constr dataTypeOf _ = hsWrapper_dataType hsWrapper_dataType :: Data.DataType hsWrapper_dataType = Data.mkDataType "HsWrapper" [ wpHole_constr, wpCompose_constr, wpFun_constr, wpCast_constr , wpEvLam_constr, wpEvApp_constr, wpTyLam_constr, wpTyApp_constr , wpLet_constr, wpMultCoercion_constr ] wpHole_constr, wpCompose_constr, wpFun_constr, wpCast_constr, wpEvLam_constr, wpEvApp_constr, wpTyLam_constr, wpTyApp_constr, wpLet_constr, wpMultCoercion_constr :: Data.Constr wpHole_constr = mkHsWrapperConstr "WpHole" wpCompose_constr = mkHsWrapperConstr "WpCompose" wpFun_constr = mkHsWrapperConstr "WpFun" wpCast_constr = mkHsWrapperConstr "WpCast" wpEvLam_constr = mkHsWrapperConstr "WpEvLam" wpEvApp_constr = mkHsWrapperConstr "WpEvApp" wpTyLam_constr = mkHsWrapperConstr "WpTyLam" wpTyApp_constr = mkHsWrapperConstr "WpTyApp" wpLet_constr = mkHsWrapperConstr "WpLet" wpMultCoercion_constr = mkHsWrapperConstr "WpMultCoercion" mkHsWrapperConstr :: String -> Data.Constr mkHsWrapperConstr name = Data.mkConstr hsWrapper_dataType name [] Data.Prefix wpFunEmpty :: HsWrapper -> HsWrapper -> Scaled TcType -> HsWrapper wpFunEmpty c1 c2 t1 = WpFun c1 c2 t1 empty (<.>) :: HsWrapper -> HsWrapper -> HsWrapper WpHole <.> c = c c <.> WpHole = c c1 <.> c2 = c1 `WpCompose` c2 mkWpFun :: HsWrapper -> HsWrapper -> (Scaled TcType) -- the "from" type of the first wrapper -> TcType -- either type of the second wrapper (used only when the -- second wrapper is the identity) -> SDoc -- what caused you to want a WpFun? Something like "When converting ..." -> HsWrapper mkWpFun WpHole WpHole _ _ _ = WpHole mkWpFun WpHole (WpCast co2) (Scaled w t1) _ _ = WpCast (mkTcFunCo Representational (multToCo w) (mkTcRepReflCo t1) co2) mkWpFun (WpCast co1) WpHole (Scaled w _) t2 _ = WpCast (mkTcFunCo Representational (multToCo w) (mkTcSymCo co1) (mkTcRepReflCo t2)) mkWpFun (WpCast co1) (WpCast co2) (Scaled w _) _ _ = WpCast (mkTcFunCo Representational (multToCo w) (mkTcSymCo co1) co2) mkWpFun co1 co2 t1 _ d = WpFun co1 co2 t1 d mkWpCastR :: TcCoercionR -> HsWrapper mkWpCastR co | isTcReflCo co = WpHole | otherwise = ASSERT2(tcCoercionRole co == Representational, ppr co) WpCast co mkWpCastN :: TcCoercionN -> HsWrapper mkWpCastN co | isTcReflCo co = WpHole | otherwise = ASSERT2(tcCoercionRole co == Nominal, ppr co) WpCast (mkTcSubCo co) -- The mkTcSubCo converts Nominal to Representational mkWpTyApps :: [Type] -> HsWrapper mkWpTyApps tys = mk_co_app_fn WpTyApp tys mkWpEvApps :: [EvTerm] -> HsWrapper mkWpEvApps args = mk_co_app_fn WpEvApp args mkWpEvVarApps :: [EvVar] -> HsWrapper mkWpEvVarApps vs = mk_co_app_fn WpEvApp (map (EvExpr . evId) vs) mkWpTyLams :: [TyVar] -> HsWrapper mkWpTyLams ids = mk_co_lam_fn WpTyLam ids mkWpLams :: [Var] -> HsWrapper mkWpLams ids = mk_co_lam_fn WpEvLam ids mkWpLet :: TcEvBinds -> HsWrapper -- This no-op is a quite a common case mkWpLet (EvBinds b) | isEmptyBag b = WpHole mkWpLet ev_binds = WpLet ev_binds mk_co_lam_fn :: (a -> HsWrapper) -> [a] -> HsWrapper mk_co_lam_fn f as = foldr (\x wrap -> f x <.> wrap) WpHole as mk_co_app_fn :: (a -> HsWrapper) -> [a] -> HsWrapper -- For applications, the *first* argument must -- come *last* in the composition sequence mk_co_app_fn f as = foldr (\x wrap -> wrap <.> f x) WpHole as idHsWrapper :: HsWrapper idHsWrapper = WpHole isIdHsWrapper :: HsWrapper -> Bool isIdHsWrapper WpHole = True isIdHsWrapper _ = False hsWrapDictBinders :: HsWrapper -> Bag DictId -- ^ Identifies the /lambda-bound/ dictionaries of an 'HsWrapper'. This is used -- (only) to allow the pattern-match overlap checker to know what Given -- dictionaries are in scope. -- -- We specifically do not collect dictionaries bound in a 'WpLet'. These are -- either superclasses of lambda-bound ones, or (extremely numerous) results of -- binding Wanted dictionaries. We definitely don't want all those cluttering -- up the Given dictionaries for pattern-match overlap checking! hsWrapDictBinders wrap = go wrap where go (WpEvLam dict_id) = unitBag dict_id go (w1 `WpCompose` w2) = go w1 `unionBags` go w2 go (WpFun _ w _ _) = go w go WpHole = emptyBag go (WpCast {}) = emptyBag go (WpEvApp {}) = emptyBag go (WpTyLam {}) = emptyBag go (WpTyApp {}) = emptyBag go (WpLet {}) = emptyBag go (WpMultCoercion {}) = emptyBag collectHsWrapBinders :: HsWrapper -> ([Var], HsWrapper) -- Collect the outer lambda binders of a HsWrapper, -- stopping as soon as you get to a non-lambda binder collectHsWrapBinders wrap = go wrap [] where -- go w ws = collectHsWrapBinders (w <.> w1 <.> ... <.> wn) go :: HsWrapper -> [HsWrapper] -> ([Var], HsWrapper) go (WpEvLam v) wraps = add_lam v (gos wraps) go (WpTyLam v) wraps = add_lam v (gos wraps) go (WpCompose w1 w2) wraps = go w1 (w2:wraps) go wrap wraps = ([], foldl' (<.>) wrap wraps) gos [] = ([], WpHole) gos (w:ws) = go w ws add_lam v (vs,w) = (v:vs, w) {- ************************************************************************ * * Evidence bindings * * ************************************************************************ -} data TcEvBinds = TcEvBinds -- Mutable evidence bindings EvBindsVar -- Mutable because they are updated "later" -- when an implication constraint is solved | EvBinds -- Immutable after zonking (Bag EvBind) data EvBindsVar = EvBindsVar { ebv_uniq :: Unique, -- The Unique is for debug printing only ebv_binds :: IORef EvBindMap, -- The main payload: the value-level evidence bindings -- (dictionaries etc) -- Some Given, some Wanted ebv_tcvs :: IORef CoVarSet -- The free Given coercion vars needed by Wanted coercions that -- are solved by filling in their HoleDest in-place. Since they -- don't appear in ebv_binds, we keep track of their free -- variables so that we can report unused given constraints -- See Note [Tracking redundant constraints] in GHC.Tc.Solver } | CoEvBindsVar { -- See Note [Coercion evidence only] -- See above for comments on ebv_uniq, ebv_tcvs ebv_uniq :: Unique, ebv_tcvs :: IORef CoVarSet } instance Data.Data TcEvBinds where -- Placeholder; we can't travers into TcEvBinds toConstr _ = abstractConstr "TcEvBinds" gunfold _ _ = error "gunfold" dataTypeOf _ = Data.mkNoRepType "TcEvBinds" {- Note [Coercion evidence only] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Class constraints etc give rise to /term/ bindings for evidence, and we have nowhere to put term bindings in /types/. So in some places we use CoEvBindsVar (see newCoTcEvBinds) to signal that no term-level evidence bindings are allowed. Notebly (): - Places in types where we are solving kind constraints (all of which are equalities); see solveEqualities - When unifying forall-types -} isCoEvBindsVar :: EvBindsVar -> Bool isCoEvBindsVar (CoEvBindsVar {}) = True isCoEvBindsVar (EvBindsVar {}) = False ----------------- newtype EvBindMap = EvBindMap { ev_bind_varenv :: DVarEnv EvBind } -- Map from evidence variables to evidence terms -- We use @DVarEnv@ here to get deterministic ordering when we -- turn it into a Bag. -- If we don't do that, when we generate let bindings for -- dictionaries in dsTcEvBinds they will be generated in random -- order. -- -- For example: -- -- let $dEq = GHC.Classes.$fEqInt in -- let $$dNum = GHC.Num.$fNumInt in ... -- -- vs -- -- let $dNum = GHC.Num.$fNumInt in -- let $dEq = GHC.Classes.$fEqInt in ... -- -- See Note [Deterministic UniqFM] in GHC.Types.Unique.DFM for explanation why -- @UniqFM@ can lead to nondeterministic order. emptyEvBindMap :: EvBindMap emptyEvBindMap = EvBindMap { ev_bind_varenv = emptyDVarEnv } extendEvBinds :: EvBindMap -> EvBind -> EvBindMap extendEvBinds bs ev_bind = EvBindMap { ev_bind_varenv = extendDVarEnv (ev_bind_varenv bs) (eb_lhs ev_bind) ev_bind } isEmptyEvBindMap :: EvBindMap -> Bool isEmptyEvBindMap (EvBindMap m) = isEmptyDVarEnv m lookupEvBind :: EvBindMap -> EvVar -> Maybe EvBind lookupEvBind bs = lookupDVarEnv (ev_bind_varenv bs) evBindMapBinds :: EvBindMap -> Bag EvBind evBindMapBinds = foldEvBindMap consBag emptyBag foldEvBindMap :: (EvBind -> a -> a) -> a -> EvBindMap -> a foldEvBindMap k z bs = foldDVarEnv k z (ev_bind_varenv bs) -- See Note [Deterministic UniqFM] to learn about nondeterminism. -- If you use this please provide a justification why it doesn't introduce -- nondeterminism. nonDetStrictFoldEvBindMap :: (EvBind -> a -> a) -> a -> EvBindMap -> a nonDetStrictFoldEvBindMap k z bs = nonDetStrictFoldDVarEnv k z (ev_bind_varenv bs) filterEvBindMap :: (EvBind -> Bool) -> EvBindMap -> EvBindMap filterEvBindMap k (EvBindMap { ev_bind_varenv = env }) = EvBindMap { ev_bind_varenv = filterDVarEnv k env } evBindMapToVarSet :: EvBindMap -> VarSet evBindMapToVarSet (EvBindMap dve) = unsafeUFMToUniqSet (mapUFM evBindVar (udfmToUfm dve)) varSetMinusEvBindMap :: VarSet -> EvBindMap -> VarSet varSetMinusEvBindMap vs (EvBindMap dve) = vs `uniqSetMinusUDFM` dve instance Outputable EvBindMap where ppr (EvBindMap m) = ppr m ----------------- -- All evidence is bound by EvBinds; no side effects data EvBind = EvBind { eb_lhs :: EvVar , eb_rhs :: EvTerm , eb_is_given :: Bool -- True <=> given -- See Note [Tracking redundant constraints] in GHC.Tc.Solver } evBindVar :: EvBind -> EvVar evBindVar = eb_lhs mkWantedEvBind :: EvVar -> EvTerm -> EvBind mkWantedEvBind ev tm = EvBind { eb_is_given = False, eb_lhs = ev, eb_rhs = tm } -- EvTypeable are never given, so we can work with EvExpr here instead of EvTerm mkGivenEvBind :: EvVar -> EvTerm -> EvBind mkGivenEvBind ev tm = EvBind { eb_is_given = True, eb_lhs = ev, eb_rhs = tm } -- An EvTerm is, conceptually, a CoreExpr that implements the constraint. -- Unfortunately, we cannot just do -- type EvTerm = CoreExpr -- Because of staging problems issues around EvTypeable data EvTerm = EvExpr EvExpr | EvTypeable Type EvTypeable -- Dictionary for (Typeable ty) | EvFun -- /\as \ds. let binds in v { et_tvs :: [TyVar] , et_given :: [EvVar] , et_binds :: TcEvBinds -- This field is why we need an EvFun -- constructor, and can't just use EvExpr , et_body :: EvVar } deriving Data.Data type EvExpr = CoreExpr -- An EvTerm is (usually) constructed by any of the constructors here -- and those more complicates ones who were moved to module GHC.Tc.Types.EvTerm -- | Any sort of evidence Id, including coercions evId :: EvId -> EvExpr evId = Var -- coercion bindings -- See Note [Coercion evidence terms] evCoercion :: TcCoercion -> EvTerm evCoercion co = EvExpr (Coercion co) -- | d |> co evCast :: EvExpr -> TcCoercion -> EvTerm evCast et tc | isReflCo tc = EvExpr et | otherwise = EvExpr (Cast et tc) -- Dictionary instance application evDFunApp :: DFunId -> [Type] -> [EvExpr] -> EvTerm evDFunApp df tys ets = EvExpr $ Var df `mkTyApps` tys `mkApps` ets evDataConApp :: DataCon -> [Type] -> [EvExpr] -> EvTerm evDataConApp dc tys ets = evDFunApp (dataConWrapId dc) tys ets -- Selector id plus the types at which it -- should be instantiated, used for HasField -- dictionaries; see Note [HasField instances] -- in TcInterface evSelector :: Id -> [Type] -> [EvExpr] -> EvExpr evSelector sel_id tys tms = Var sel_id `mkTyApps` tys `mkApps` tms -- Dictionary for (Typeable ty) evTypeable :: Type -> EvTypeable -> EvTerm evTypeable = EvTypeable -- | Instructions on how to make a 'Typeable' dictionary. -- See Note [Typeable evidence terms] data EvTypeable = EvTypeableTyCon TyCon [EvTerm] -- ^ Dictionary for @Typeable T@ where @T@ is a type constructor with all of -- its kind variables saturated. The @[EvTerm]@ is @Typeable@ evidence for -- the applied kinds.. | EvTypeableTyApp EvTerm EvTerm -- ^ Dictionary for @Typeable (s t)@, -- given a dictionaries for @s@ and @t@. | EvTypeableTrFun EvTerm EvTerm EvTerm -- ^ Dictionary for @Typeable (s # w -> t)@, -- given a dictionaries for @w@, @s@, and @t@. | EvTypeableTyLit EvTerm -- ^ Dictionary for a type literal, -- e.g. @Typeable "foo"@ or @Typeable 3@ -- The 'EvTerm' is evidence of, e.g., @KnownNat 3@ -- (see #10348) deriving Data.Data -- | Evidence for @CallStack@ implicit parameters. data EvCallStack -- See Note [Overview of implicit CallStacks] = EvCsEmpty | EvCsPushCall Name RealSrcSpan EvExpr -- ^ @EvCsPushCall name loc stk@ represents a call to @name@, occurring at -- @loc@, in a calling context @stk@. deriving Data.Data {- ************************************************************************ * * Evidence for holes * * ************************************************************************ -} -- | Where to store evidence for expression holes -- See Note [Holes] in GHC.Tc.Types.Constraint data HoleExprRef = HER (IORef EvTerm) -- ^ where to write the erroring expression TcType -- ^ expected type of that expression Unique -- ^ for debug output only instance Outputable HoleExprRef where ppr (HER _ _ u) = ppr u instance Data.Data HoleExprRef where -- Placeholder; we can't traverse into HoleExprRef toConstr _ = abstractConstr "HoleExprRef" gunfold _ _ = error "gunfold" dataTypeOf _ = Data.mkNoRepType "HoleExprRef" {- Note [Typeable evidence terms] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The EvTypeable data type looks isomorphic to Type, but the EvTerms inside can be EvIds. Eg f :: forall a. Typeable a => a -> TypeRep f x = typeRep (undefined :: Proxy [a]) Here for the (Typeable [a]) dictionary passed to typeRep we make evidence dl :: Typeable [a] = EvTypeable [a] (EvTypeableTyApp (EvTypeableTyCon []) (EvId d)) where d :: Typable a is the lambda-bound dictionary passed into f. Note [Coercion evidence terms] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A "coercion evidence term" takes one of these forms co_tm ::= EvId v where v :: t1 ~# t2 | EvCoercion co | EvCast co_tm co We do quite often need to get a TcCoercion from an EvTerm; see 'evTermCoercion'. INVARIANT: The evidence for any constraint with type (t1 ~# t2) is a coercion evidence term. Consider for example [G] d :: F Int a If we have ax7 a :: F Int a ~ (a ~ Bool) then we do NOT generate the constraint [G] (d |> ax7 a) :: a ~ Bool because that does not satisfy the invariant (d is not a coercion variable). Instead we make a binding g1 :: a~Bool = g |> ax7 a and the constraint [G] g1 :: a~Bool See #7238 and Note [Bind new Givens immediately] in GHC.Tc.Types.Constraint Note [EvBinds/EvTerm] ~~~~~~~~~~~~~~~~~~~~~ How evidence is created and updated. Bindings for dictionaries, and coercions and implicit parameters are carried around in TcEvBinds which during constraint generation and simplification is always of the form (TcEvBinds ref). After constraint simplification is finished it will be transformed to t an (EvBinds ev_bag). Evidence for coercions *SHOULD* be filled in using the TcEvBinds However, all EvVars that correspond to *wanted* coercion terms in an EvBind must be mutable variables so that they can be readily inlined (by zonking) after constraint simplification is finished. Conclusion: a new wanted coercion variable should be made mutable. [Notice though that evidence variables that bind coercion terms from super classes will be "given" and hence rigid] Note [Overview of implicit CallStacks] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (See https://gitlab.haskell.org/ghc/ghc/wikis/explicit-call-stack/implicit-locations) The goal of CallStack evidence terms is to reify locations in the program source as runtime values, without any support from the RTS. We accomplish this by assigning a special meaning to constraints of type GHC.Stack.Types.HasCallStack, an alias type HasCallStack = (?callStack :: CallStack) Implicit parameters of type GHC.Stack.Types.CallStack (the name is not important) are solved in three steps: 1. Occurrences of CallStack IPs are solved directly from the given IP, just like a regular IP. For example, the occurrence of `?stk` in error :: (?stk :: CallStack) => String -> a error s = raise (ErrorCall (s ++ prettyCallStack ?stk)) will be solved for the `?stk` in `error`s context as before. 2. In a function call, instead of simply passing the given IP, we first append the current call-site to it. For example, consider a call to the callstack-aware `error` above. undefined :: (?stk :: CallStack) => a undefined = error "undefined!" Here we want to take the given `?stk` and append the current call-site, before passing it to `error`. In essence, we want to rewrite `error "undefined!"` to let ?stk = pushCallStack ?stk in error "undefined!" We achieve this effect by emitting a NEW wanted [W] d :: IP "stk" CallStack from which we build the evidence term EvCsPushCall "error" (EvId d) that we use to solve the call to `error`. The new wanted `d` will then be solved per rule (1), ie as a regular IP. (see GHC.Tc.Solver.Interact.interactDict) 3. We default any insoluble CallStacks to the empty CallStack. Suppose `undefined` did not request a CallStack, ie undefinedNoStk :: a undefinedNoStk = error "undefined!" Under the usual IP rules, the new wanted from rule (2) would be insoluble as there's no given IP from which to solve it, so we would get an "unbound implicit parameter" error. We don't ever want to emit an insoluble CallStack IP, so we add a defaulting pass to default any remaining wanted CallStacks to the empty CallStack with the evidence term EvCsEmpty (see GHC.Tc.Solver.simplifyTopWanteds and GHC.Tc.Solver.defaultCallStacks) This provides a lightweight mechanism for building up call-stacks explicitly, but is notably limited by the fact that the stack will stop at the first function whose type does not include a CallStack IP. For example, using the above definition of `undefined`: head :: [a] -> a head [] = undefined head (x:_) = x g = head [] the resulting CallStack will include the call to `undefined` in `head` and the call to `error` in `undefined`, but *not* the call to `head` in `g`, because `head` did not explicitly request a CallStack. Important Details: - GHC should NEVER report an insoluble CallStack constraint. - GHC should NEVER infer a CallStack constraint unless one was requested with a partial type signature (See TcType.pickQuantifiablePreds). - A CallStack (defined in GHC.Stack.Types) is a [(String, SrcLoc)], where the String is the name of the binder that is used at the SrcLoc. SrcLoc is also defined in GHC.Stack.Types and contains the package/module/file name, as well as the full source-span. Both CallStack and SrcLoc are kept abstract so only GHC can construct new values. - We will automatically solve any wanted CallStack regardless of the name of the IP, i.e. f = show (?stk :: CallStack) g = show (?loc :: CallStack) are both valid. However, we will only push new SrcLocs onto existing CallStacks when the IP names match, e.g. in head :: (?loc :: CallStack) => [a] -> a head [] = error (show (?stk :: CallStack)) the printed CallStack will NOT include head's call-site. This reflects the standard scoping rules of implicit-parameters. - An EvCallStack term desugars to a CoreExpr of type `IP "some str" CallStack`. The desugarer will need to unwrap the IP newtype before pushing a new call-site onto a given stack (See GHC.HsToCore.Binds.dsEvCallStack) - When we emit a new wanted CallStack from rule (2) we set its origin to `IPOccOrigin ip_name` instead of the original `OccurrenceOf func` (see GHC.Tc.Solver.Interact.interactDict). This is a bit shady, but is how we ensure that the new wanted is solved like a regular IP. -} mkEvCast :: EvExpr -> TcCoercion -> EvTerm mkEvCast ev lco | ASSERT2( tcCoercionRole lco == Representational , (vcat [text "Coercion of wrong role passed to mkEvCast:", ppr ev, ppr lco])) isTcReflCo lco = EvExpr ev | otherwise = evCast ev lco mkEvScSelectors -- Assume class (..., D ty, ...) => C a b :: Class -> [TcType] -- C ty1 ty2 -> [(TcPredType, -- D ty[ty1/a,ty2/b] EvExpr) -- :: C ty1 ty2 -> D ty[ty1/a,ty2/b] ] mkEvScSelectors cls tys = zipWith mk_pr (immSuperClasses cls tys) [0..] where mk_pr pred i = (pred, Var sc_sel_id `mkTyApps` tys) where sc_sel_id = classSCSelId cls i -- Zero-indexed emptyTcEvBinds :: TcEvBinds emptyTcEvBinds = EvBinds emptyBag isEmptyTcEvBinds :: TcEvBinds -> Bool isEmptyTcEvBinds (EvBinds b) = isEmptyBag b isEmptyTcEvBinds (TcEvBinds {}) = panic "isEmptyTcEvBinds" evTermCoercion_maybe :: EvTerm -> Maybe TcCoercion -- Applied only to EvTerms of type (s~t) -- See Note [Coercion evidence terms] evTermCoercion_maybe ev_term | EvExpr e <- ev_term = go e | otherwise = Nothing where go :: EvExpr -> Maybe TcCoercion go (Var v) = return (mkCoVarCo v) go (Coercion co) = return co go (Cast tm co) = do { co' <- go tm ; return (mkCoCast co' co) } go _ = Nothing evTermCoercion :: EvTerm -> TcCoercion evTermCoercion tm = case evTermCoercion_maybe tm of Just co -> co Nothing -> pprPanic "evTermCoercion" (ppr tm) {- ********************************************************************* * * Free variables * * ********************************************************************* -} findNeededEvVars :: EvBindMap -> VarSet -> VarSet -- Find all the Given evidence needed by seeds, -- looking transitively through binds findNeededEvVars ev_binds seeds = transCloVarSet also_needs seeds where also_needs :: VarSet -> VarSet also_needs needs = nonDetStrictFoldUniqSet add emptyVarSet needs -- It's OK to use a non-deterministic fold here because we immediately -- forget about the ordering by creating a set add :: Var -> VarSet -> VarSet add v needs | Just ev_bind <- lookupEvBind ev_binds v , EvBind { eb_is_given = is_given, eb_rhs = rhs } <- ev_bind , is_given = evVarsOfTerm rhs `unionVarSet` needs | otherwise = needs evVarsOfTerm :: EvTerm -> VarSet evVarsOfTerm (EvExpr e) = exprSomeFreeVars isEvVar e evVarsOfTerm (EvTypeable _ ev) = evVarsOfTypeable ev evVarsOfTerm (EvFun {}) = emptyVarSet -- See Note [Free vars of EvFun] evVarsOfTerms :: [EvTerm] -> VarSet evVarsOfTerms = mapUnionVarSet evVarsOfTerm evVarsOfTypeable :: EvTypeable -> VarSet evVarsOfTypeable ev = case ev of EvTypeableTyCon _ e -> mapUnionVarSet evVarsOfTerm e EvTypeableTyApp e1 e2 -> evVarsOfTerms [e1,e2] EvTypeableTrFun em e1 e2 -> evVarsOfTerms [em,e1,e2] EvTypeableTyLit e -> evVarsOfTerm e {- Note [Free vars of EvFun] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Finding the free vars of an EvFun is made tricky by the fact the bindings et_binds may be a mutable variable. Fortunately, we can just squeeze by. Here's how. * evVarsOfTerm is used only by GHC.Tc.Solver.neededEvVars. * Each EvBindsVar in an et_binds field of an EvFun is /also/ in the ic_binds field of an Implication * So we can track usage via the processing for that implication, (see Note [Tracking redundant constraints] in GHC.Tc.Solver). We can ignore usage from the EvFun altogether. ************************************************************************ * * Pretty printing * * ************************************************************************ -} instance Outputable HsWrapper where ppr co_fn = pprHsWrapper co_fn (no_parens (text "<>")) pprHsWrapper :: HsWrapper -> (Bool -> SDoc) -> SDoc -- With -fprint-typechecker-elaboration, print the wrapper -- otherwise just print what's inside -- The pp_thing_inside function takes Bool to say whether -- it's in a position that needs parens for a non-atomic thing pprHsWrapper wrap pp_thing_inside = sdocOption sdocPrintTypecheckerElaboration $ \case True -> help pp_thing_inside wrap False False -> pp_thing_inside False where help :: (Bool -> SDoc) -> HsWrapper -> Bool -> SDoc -- True <=> appears in function application position -- False <=> appears as body of let or lambda help it WpHole = it help it (WpCompose f1 f2) = help (help it f2) f1 help it (WpFun f1 f2 (Scaled w t1) _) = add_parens $ text "\\(x" <> dcolon <> brackets (ppr w) <> ppr t1 <> text ")." <+> help (\_ -> it True <+> help (\_ -> text "x") f1 True) f2 False help it (WpCast co) = add_parens $ sep [it False, nest 2 (text "|>" <+> pprParendCo co)] help it (WpEvApp id) = no_parens $ sep [it True, nest 2 (ppr id)] help it (WpTyApp ty) = no_parens $ sep [it True, text "@" <> pprParendType ty] help it (WpEvLam id) = add_parens $ sep [ text "\\" <> pprLamBndr id <> dot, it False] help it (WpTyLam tv) = add_parens $ sep [text "/\\" <> pprLamBndr tv <> dot, it False] help it (WpLet binds) = add_parens $ sep [text "let" <+> braces (ppr binds), it False] help it (WpMultCoercion co) = add_parens $ sep [it False, nest 2 (text "" <+> pprParendCo co)] pprLamBndr :: Id -> SDoc pprLamBndr v = pprBndr LambdaBind v add_parens, no_parens :: SDoc -> Bool -> SDoc add_parens d True = parens d add_parens d False = d no_parens d _ = d instance Outputable TcEvBinds where ppr (TcEvBinds v) = ppr v ppr (EvBinds bs) = text "EvBinds" <> braces (vcat (map ppr (bagToList bs))) instance Outputable EvBindsVar where ppr (EvBindsVar { ebv_uniq = u }) = text "EvBindsVar" <> angleBrackets (ppr u) ppr (CoEvBindsVar { ebv_uniq = u }) = text "CoEvBindsVar" <> angleBrackets (ppr u) instance Uniquable EvBindsVar where getUnique = ebv_uniq instance Outputable EvBind where ppr (EvBind { eb_lhs = v, eb_rhs = e, eb_is_given = is_given }) = sep [ pp_gw <+> ppr v , nest 2 $ equals <+> ppr e ] where pp_gw = brackets (if is_given then char 'G' else char 'W') -- We cheat a bit and pretend EqVars are CoVars for the purposes of pretty printing instance Outputable EvTerm where ppr (EvExpr e) = ppr e ppr (EvTypeable ty ev) = ppr ev <+> dcolon <+> text "Typeable" <+> ppr ty ppr (EvFun { et_tvs = tvs, et_given = gs, et_binds = bs, et_body = w }) = hang (text "\\" <+> sep (map pprLamBndr (tvs ++ gs)) <+> arrow) 2 (ppr bs $$ ppr w) -- Not very pretty instance Outputable EvCallStack where ppr EvCsEmpty = text "[]" ppr (EvCsPushCall name loc tm) = ppr (name,loc) <+> text ":" <+> ppr tm instance Outputable EvTypeable where ppr (EvTypeableTyCon ts _) = text "TyCon" <+> ppr ts ppr (EvTypeableTyApp t1 t2) = parens (ppr t1 <+> ppr t2) ppr (EvTypeableTrFun tm t1 t2) = parens (ppr t1 <+> mulArrow (ppr tm) <+> ppr t2) ppr (EvTypeableTyLit t1) = text "TyLit" <> ppr t1 ---------------------------------------------------------------------- -- Helper functions for dealing with IP newtype-dictionaries ---------------------------------------------------------------------- -- | Create a 'Coercion' that unwraps an implicit-parameter or -- overloaded-label dictionary to expose the underlying value. We -- expect the 'Type' to have the form `IP sym ty` or `IsLabel sym ty`, -- and return a 'Coercion' `co :: IP sym ty ~ ty` or -- `co :: IsLabel sym ty ~ ty`. See also -- Note [Type-checking overloaded labels] in "GHC.Tc.Gen.Expr". unwrapIP :: Type -> CoercionR unwrapIP ty = case unwrapNewTyCon_maybe tc of Just (_,_,ax) -> mkUnbranchedAxInstCo Representational ax tys [] Nothing -> pprPanic "unwrapIP" $ text "The dictionary for" <+> quotes (ppr tc) <+> text "is not a newtype!" where (tc, tys) = splitTyConApp ty -- | Create a 'Coercion' that wraps a value in an implicit-parameter -- dictionary. See 'unwrapIP'. wrapIP :: Type -> CoercionR wrapIP ty = mkSymCo (unwrapIP ty) ---------------------------------------------------------------------- -- A datatype used to pass information when desugaring quotations ---------------------------------------------------------------------- -- We have to pass a `EvVar` and `Type` into `dsBracket` so that the -- correct evidence and types are applied to all the TH combinators. -- This data type bundles them up together with some convenience methods. -- -- The EvVar is evidence for `Quote m` -- The Type is a metavariable for `m` -- data QuoteWrapper = QuoteWrapper EvVar Type deriving Data.Data quoteWrapperTyVarTy :: QuoteWrapper -> Type quoteWrapperTyVarTy (QuoteWrapper _ t) = t -- | Convert the QuoteWrapper into a normal HsWrapper which can be used to -- apply its contents. applyQuoteWrapper :: QuoteWrapper -> HsWrapper applyQuoteWrapper (QuoteWrapper ev_var m_var) = mkWpEvVarApps [ev_var] <.> mkWpTyApps [m_var]