{- (c) The University of Glasgow 2006-2012 (c) The GRASP Project, Glasgow University, 1992-2002 Various types used during typechecking, please see TcRnMonad as well for operations on these types. You probably want to import it, instead of this module. All the monads exported here are built on top of the same IOEnv monad. The monad functions like a Reader monad in the way it passes the environment around. This is done to allow the environment to be manipulated in a stack like fashion when entering expressions... ect. For state that is global and should be returned at the end (e.g not part of the stack mechanism), you should use an TcRef (= IORef) to store them. -} {-# LANGUAGE CPP, ExistentialQuantification, GeneralizedNewtypeDeriving, ViewPatterns #-} module TcRnTypes( TcRnIf, TcRn, TcM, RnM, IfM, IfL, IfG, -- The monad is opaque outside this module TcRef, -- The environment types Env(..), TcGblEnv(..), TcLclEnv(..), IfGblEnv(..), IfLclEnv(..), tcVisibleOrphanMods, -- Frontend types (shouldn't really be here) FrontendResult(..), -- Renamer types ErrCtxt, RecFieldEnv, ImportAvails(..), emptyImportAvails, plusImportAvails, WhereFrom(..), mkModDeps, -- Typechecker types TcTypeEnv, TcIdBinderStack, TcIdBinder(..), TcTyThing(..), PromotionErr(..), SelfBootInfo(..), pprTcTyThingCategory, pprPECategory, -- Desugaring types DsM, DsLclEnv(..), DsGblEnv(..), PArrBuiltin(..), DsMetaEnv, DsMetaVal(..), -- Template Haskell ThStage(..), SpliceType(..), PendingStuff(..), topStage, topAnnStage, topSpliceStage, ThLevel, impLevel, outerLevel, thLevel, -- Arrows ArrowCtxt(..), -- TcSigInfo TcSigFun, TcSigInfo(..), TcIdSigInfo(..), TcPatSynInfo(..), TcIdSigBndr(..), findScopedTyVars, isPartialSig, noCompleteSig, tcSigInfoName, completeIdSigPolyId, completeSigPolyId_maybe, completeIdSigPolyId_maybe, -- Canonical constraints Xi, Ct(..), Cts, emptyCts, andCts, andManyCts, pprCts, singleCt, listToCts, ctsElts, consCts, snocCts, extendCtsList, isEmptyCts, isCTyEqCan, isCFunEqCan, isPendingScDict, superClassesMightHelp, isCDictCan_Maybe, isCFunEqCan_maybe, isCIrredEvCan, isCNonCanonical, isWantedCt, isDerivedCt, isGivenCt, isHoleCt, isOutOfScopeCt, isExprHoleCt, isTypeHoleCt, isUserTypeErrorCt, getUserTypeErrorMsg, ctEvidence, ctLoc, setCtLoc, ctPred, ctFlavour, ctEqRel, ctOrigin, mkTcEqPredLikeEv, mkNonCanonical, mkNonCanonicalCt, mkGivens, ctEvPred, ctEvLoc, ctEvOrigin, ctEvEqRel, ctEvTerm, ctEvCoercion, ctEvId, tyCoVarsOfCt, tyCoVarsOfCts, tyCoVarsOfCtList, tyCoVarsOfCtsList, toDerivedCt, WantedConstraints(..), insolubleWC, emptyWC, isEmptyWC, toDerivedWC, andWC, unionsWC, mkSimpleWC, mkImplicWC, addInsols, getInsolubles, addSimples, addImplics, tyCoVarsOfWC, dropDerivedWC, dropDerivedSimples, dropDerivedInsols, tyCoVarsOfWCList, isDroppableDerivedLoc, insolubleImplic, arisesFromGivens, Implication(..), ImplicStatus(..), isInsolubleStatus, SubGoalDepth, initialSubGoalDepth, bumpSubGoalDepth, subGoalDepthExceeded, CtLoc(..), ctLocSpan, ctLocEnv, ctLocLevel, ctLocOrigin, ctLocTypeOrKind_maybe, ctLocDepth, bumpCtLocDepth, setCtLocOrigin, setCtLocEnv, setCtLocSpan, CtOrigin(..), exprCtOrigin, matchesCtOrigin, grhssCtOrigin, ErrorThing(..), mkErrorThing, errorThingNumArgs_maybe, TypeOrKind(..), isTypeLevel, isKindLevel, pprCtOrigin, pprCtLoc, pushErrCtxt, pushErrCtxtSameOrigin, SkolemInfo(..), pprSigSkolInfo, pprSkolInfo, CtEvidence(..), TcEvDest(..), mkGivenLoc, mkKindLoc, toKindLoc, isWanted, isGiven, isDerived, ctEvRole, -- Constraint solver plugins TcPlugin(..), TcPluginResult(..), TcPluginSolver, TcPluginM, runTcPluginM, unsafeTcPluginTcM, getEvBindsTcPluginM_maybe, CtFlavour(..), ctEvFlavour, CtFlavourRole, ctEvFlavourRole, ctFlavourRole, eqCanRewrite, eqCanRewriteFR, eqCanDischarge, funEqCanDischarge, funEqCanDischargeFR, -- Pretty printing pprEvVarTheta, pprEvVars, pprEvVarWithType, -- Misc other types TcId, TcIdSet, Hole(..), holeOcc ) where #include "HsVersions.h" import HsSyn import CoreSyn import HscTypes import TcEvidence import Type import Class ( Class ) import TyCon ( TyCon ) import Coercion ( Coercion, mkHoleCo ) import ConLike ( ConLike(..) ) import DataCon ( DataCon, dataConUserType, dataConOrigArgTys ) import PatSyn ( PatSyn, pprPatSynType ) import Id ( idName ) import FieldLabel ( FieldLabel ) import TcType import Annotations import InstEnv import FamInstEnv import PmExpr import IOEnv import RdrName import Name import NameEnv import NameSet import Avail import Var import FV import VarEnv import Module import SrcLoc import VarSet import ErrUtils import UniqFM import UniqSupply import BasicTypes import Bag import DynFlags import Outputable import ListSetOps import FastString import GHC.Fingerprint import qualified GHC.LanguageExtensions as LangExt import Control.Monad (ap, liftM, msum) #if __GLASGOW_HASKELL__ > 710 import qualified Control.Monad.Fail as MonadFail #endif import Data.Set ( Set ) #ifdef GHCI import Data.Map ( Map ) import Data.Dynamic ( Dynamic ) import Data.Typeable ( TypeRep ) import GHCi.Message import GHCi.RemoteTypes import qualified Language.Haskell.TH as TH #endif {- ************************************************************************ * * Standard monad definition for TcRn All the combinators for the monad can be found in TcRnMonad * * ************************************************************************ The monad itself has to be defined here, because it is mentioned by ErrCtxt -} type TcRnIf a b = IOEnv (Env a b) type TcRn = TcRnIf TcGblEnv TcLclEnv -- Type inference type IfM lcl = TcRnIf IfGblEnv lcl -- Iface stuff type IfG = IfM () -- Top level type IfL = IfM IfLclEnv -- Nested type DsM = TcRnIf DsGblEnv DsLclEnv -- Desugaring -- TcRn is the type-checking and renaming monad: the main monad that -- most type-checking takes place in. The global environment is -- 'TcGblEnv', which tracks all of the top-level type-checking -- information we've accumulated while checking a module, while the -- local environment is 'TcLclEnv', which tracks local information as -- we move inside expressions. -- | Historical "renaming monad" (now it's just 'TcRn'). type RnM = TcRn -- | Historical "type-checking monad" (now it's just 'TcRn'). type TcM = TcRn -- We 'stack' these envs through the Reader like monad infrastructure -- as we move into an expression (although the change is focused in -- the lcl type). data Env gbl lcl = Env { env_top :: HscEnv, -- Top-level stuff that never changes -- Includes all info about imported things env_us :: {-# UNPACK #-} !(IORef UniqSupply), -- Unique supply for local variables env_gbl :: gbl, -- Info about things defined at the top level -- of the module being compiled env_lcl :: lcl -- Nested stuff; changes as we go into } instance ContainsDynFlags (Env gbl lcl) where extractDynFlags env = hsc_dflags (env_top env) instance ContainsModule gbl => ContainsModule (Env gbl lcl) where extractModule env = extractModule (env_gbl env) {- ************************************************************************ * * The interface environments Used when dealing with IfaceDecls * * ************************************************************************ -} data IfGblEnv = IfGblEnv { -- Some information about where this environment came from; -- useful for debugging. if_doc :: SDoc, -- The type environment for the module being compiled, -- in case the interface refers back to it via a reference that -- was originally a hi-boot file. -- We need the module name so we can test when it's appropriate -- to look in this env. if_rec_types :: Maybe (Module, IfG TypeEnv) -- Allows a read effect, so it can be in a mutable -- variable; c.f. handling the external package type env -- Nothing => interactive stuff, no loops possible } data IfLclEnv = IfLclEnv { -- The module for the current IfaceDecl -- So if we see f = \x -> x -- it means M.f = \x -> x, where M is the if_mod if_mod :: Module, -- The field is used only for error reporting -- if (say) there's a Lint error in it if_loc :: SDoc, -- Where the interface came from: -- .hi file, or GHCi state, or ext core -- plus which bit is currently being examined if_tv_env :: FastStringEnv TyVar, -- Nested tyvar bindings if_id_env :: FastStringEnv Id -- Nested id binding } {- ************************************************************************ * * Desugarer monad * * ************************************************************************ Now the mondo monad magic (yes, @DsM@ is a silly name)---carry around a @UniqueSupply@ and some annotations, which presumably include source-file location information: -} -- If '-XParallelArrays' is given, the desugarer populates this table with the corresponding -- variables found in 'Data.Array.Parallel'. -- data PArrBuiltin = PArrBuiltin { lengthPVar :: Var -- ^ lengthP , replicatePVar :: Var -- ^ replicateP , singletonPVar :: Var -- ^ singletonP , mapPVar :: Var -- ^ mapP , filterPVar :: Var -- ^ filterP , zipPVar :: Var -- ^ zipP , crossMapPVar :: Var -- ^ crossMapP , indexPVar :: Var -- ^ (!:) , emptyPVar :: Var -- ^ emptyP , appPVar :: Var -- ^ (+:+) , enumFromToPVar :: Var -- ^ enumFromToP , enumFromThenToPVar :: Var -- ^ enumFromThenToP } data DsGblEnv = DsGblEnv { ds_mod :: Module -- For SCC profiling , ds_fam_inst_env :: FamInstEnv -- Like tcg_fam_inst_env , ds_unqual :: PrintUnqualified , ds_msgs :: IORef Messages -- Warning messages , ds_if_env :: (IfGblEnv, IfLclEnv) -- Used for looking up global, -- possibly-imported things , ds_dph_env :: GlobalRdrEnv -- exported entities of 'Data.Array.Parallel.Prim' -- iff '-fvectorise' flag was given as well as -- exported entities of 'Data.Array.Parallel' iff -- '-XParallelArrays' was given; otherwise, empty , ds_parr_bi :: PArrBuiltin -- desugarar names for '-XParallelArrays' , ds_static_binds :: IORef [(Fingerprint, (Id,CoreExpr))] -- ^ Bindings resulted from floating static forms } instance ContainsModule DsGblEnv where extractModule = ds_mod data DsLclEnv = DsLclEnv { dsl_meta :: DsMetaEnv, -- Template Haskell bindings dsl_loc :: RealSrcSpan, -- To put in pattern-matching error msgs dsl_dicts :: Bag EvVar, -- Constraints from GADT pattern-matching dsl_tm_cs :: Bag SimpleEq, dsl_pm_iter :: IORef Int -- no iterations for pmcheck } -- Inside [| |] brackets, the desugarer looks -- up variables in the DsMetaEnv type DsMetaEnv = NameEnv DsMetaVal data DsMetaVal = DsBound Id -- Bound by a pattern inside the [| |]. -- Will be dynamically alpha renamed. -- The Id has type THSyntax.Var | DsSplice (HsExpr Id) -- These bindings are introduced by -- the PendingSplices on a HsBracketOut {- ************************************************************************ * * Global typechecker environment * * ************************************************************************ -} -- | 'FrontendResult' describes the result of running the -- frontend of a Haskell module. Usually, you'll get -- a 'FrontendTypecheck', since running the frontend involves -- typechecking a program, but for an hs-boot merge you'll -- just get a ModIface, since no actual typechecking occurred. -- -- This data type really should be in HscTypes, but it needs -- to have a TcGblEnv which is only defined here. data FrontendResult = FrontendTypecheck TcGblEnv -- | 'TcGblEnv' describes the top-level of the module at the -- point at which the typechecker is finished work. -- It is this structure that is handed on to the desugarer -- For state that needs to be updated during the typechecking -- phase and returned at end, use a 'TcRef' (= 'IORef'). data TcGblEnv = TcGblEnv { tcg_mod :: Module, -- ^ Module being compiled tcg_src :: HscSource, -- ^ What kind of module (regular Haskell, hs-boot, hsig) tcg_sig_of :: Maybe Module, -- ^ Are we being compiled as a signature of an implementation? tcg_impl_rdr_env :: Maybe GlobalRdrEnv, -- ^ Environment used only during -sig-of for resolving top level -- bindings. See Note [Signature parameters in TcGblEnv and DynFlags] tcg_rdr_env :: GlobalRdrEnv, -- ^ Top level envt; used during renaming tcg_default :: Maybe [Type], -- ^ Types used for defaulting. @Nothing@ => no @default@ decl tcg_fix_env :: FixityEnv, -- ^ Just for things in this module tcg_field_env :: RecFieldEnv, -- ^ Just for things in this module -- See Note [The interactive package] in HscTypes tcg_type_env :: TypeEnv, -- ^ Global type env for the module we are compiling now. All -- TyCons and Classes (for this module) end up in here right away, -- along with their derived constructors, selectors. -- -- (Ids defined in this module start in the local envt, though they -- move to the global envt during zonking) -- -- NB: for what "things in this module" means, see -- Note [The interactive package] in HscTypes tcg_type_env_var :: TcRef TypeEnv, -- Used only to initialise the interface-file -- typechecker in initIfaceTcRn, so that it can see stuff -- bound in this module when dealing with hi-boot recursions -- Updated at intervals (e.g. after dealing with types and classes) tcg_inst_env :: InstEnv, -- ^ Instance envt for all /home-package/ modules; -- Includes the dfuns in tcg_insts tcg_fam_inst_env :: FamInstEnv, -- ^ Ditto for family instances tcg_ann_env :: AnnEnv, -- ^ And for annotations -- Now a bunch of things about this module that are simply -- accumulated, but never consulted until the end. -- Nevertheless, it's convenient to accumulate them along -- with the rest of the info from this module. tcg_exports :: [AvailInfo], -- ^ What is exported tcg_imports :: ImportAvails, -- ^ Information about what was imported from where, including -- things bound in this module. Also store Safe Haskell info -- here about transative trusted packaage requirements. tcg_dus :: DefUses, -- ^ What is defined in this module and what is used. tcg_used_gres :: TcRef [GlobalRdrElt], -- ^ Records occurrences of imported entities -- See Note [Tracking unused binding and imports] tcg_keep :: TcRef NameSet, -- ^ Locally-defined top-level names to keep alive. -- -- "Keep alive" means give them an Exported flag, so that the -- simplifier does not discard them as dead code, and so that they -- are exposed in the interface file (but not to export to the -- user). -- -- Some things, like dict-fun Ids and default-method Ids are "born" -- with the Exported flag on, for exactly the above reason, but some -- we only discover as we go. Specifically: -- -- * The to/from functions for generic data types -- -- * Top-level variables appearing free in the RHS of an orphan -- rule -- -- * Top-level variables appearing free in a TH bracket tcg_th_used :: TcRef Bool, -- ^ @True@ <=> Template Haskell syntax used. -- -- We need this so that we can generate a dependency on the -- Template Haskell package, because the desugarer is going -- to emit loads of references to TH symbols. The reference -- is implicit rather than explicit, so we have to zap a -- mutable variable. tcg_th_splice_used :: TcRef Bool, -- ^ @True@ <=> A Template Haskell splice was used. -- -- Splices disable recompilation avoidance (see #481) tcg_th_top_level_locs :: TcRef (Set RealSrcSpan), -- ^ Locations of the top-level splices; used for providing details on -- scope in error messages for out-of-scope variables tcg_dfun_n :: TcRef OccSet, -- ^ Allows us to choose unique DFun names. -- The next fields accumulate the payload of the module -- The binds, rules and foreign-decl fields are collected -- initially in un-zonked form and are finally zonked in tcRnSrcDecls tcg_rn_exports :: Maybe [Located (IE Name)], -- Nothing <=> no explicit export list -- Is always Nothing if we don't want to retain renamed -- exports tcg_rn_imports :: [LImportDecl Name], -- Keep the renamed imports regardless. They are not -- voluminous and are needed if you want to report unused imports tcg_rn_decls :: Maybe (HsGroup Name), -- ^ Renamed decls, maybe. @Nothing@ <=> Don't retain renamed -- decls. tcg_dependent_files :: TcRef [FilePath], -- ^ dependencies from addDependentFile #ifdef GHCI tcg_th_topdecls :: TcRef [LHsDecl RdrName], -- ^ Top-level declarations from addTopDecls tcg_th_topnames :: TcRef NameSet, -- ^ Exact names bound in top-level declarations in tcg_th_topdecls tcg_th_modfinalizers :: TcRef [TcM ()], -- ^ Template Haskell module finalizers. -- -- They are computations in the @TcM@ monad rather than @Q@ because we -- set them to use particular local environments. tcg_th_state :: TcRef (Map TypeRep Dynamic), tcg_th_remote_state :: TcRef (Maybe (ForeignRef (IORef QState))), -- ^ Template Haskell state #endif /* GHCI */ tcg_ev_binds :: Bag EvBind, -- Top-level evidence bindings -- Things defined in this module, or (in GHCi) -- in the declarations for a single GHCi command. -- For the latter, see Note [The interactive package] in HscTypes tcg_tr_module :: Maybe Id, -- Id for $trModule :: GHC.Types.Module -- for which every module has a top-level defn -- except in GHCi in which case we have Nothing tcg_binds :: LHsBinds Id, -- Value bindings in this module tcg_sigs :: NameSet, -- ...Top-level names that *lack* a signature tcg_imp_specs :: [LTcSpecPrag], -- ...SPECIALISE prags for imported Ids tcg_warns :: Warnings, -- ...Warnings and deprecations tcg_anns :: [Annotation], -- ...Annotations tcg_tcs :: [TyCon], -- ...TyCons and Classes tcg_insts :: [ClsInst], -- ...Instances tcg_fam_insts :: [FamInst], -- ...Family instances tcg_rules :: [LRuleDecl Id], -- ...Rules tcg_fords :: [LForeignDecl Id], -- ...Foreign import & exports tcg_vects :: [LVectDecl Id], -- ...Vectorisation declarations tcg_patsyns :: [PatSyn], -- ...Pattern synonyms tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the -- prog uses hpc instrumentation. tcg_self_boot :: SelfBootInfo, -- ^ Whether this module has a -- corresponding hi-boot file tcg_main :: Maybe Name, -- ^ The Name of the main -- function, if this module is -- the main module. tcg_safeInfer :: TcRef (Bool, WarningMessages), -- ^ Has the typechecker inferred this module as -XSafe (Safe Haskell) -- See Note [Safe Haskell Overlapping Instances Implementation], -- although this is used for more than just that failure case. tcg_tc_plugins :: [TcPluginSolver], -- ^ A list of user-defined plugins for the constraint solver. tcg_static_wc :: TcRef WantedConstraints -- ^ Wanted constraints of static forms. } tcVisibleOrphanMods :: TcGblEnv -> ModuleSet tcVisibleOrphanMods tcg_env = mkModuleSet (tcg_mod tcg_env : imp_orphs (tcg_imports tcg_env)) -- Note [Signature parameters in TcGblEnv and DynFlags] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- When compiling signature files, we need to know which implementation -- we've actually linked against the signature. There are three seemingly -- redundant places where this information is stored: in DynFlags, there -- is sigOf, and in TcGblEnv, there is tcg_sig_of and tcg_impl_rdr_env. -- Here's the difference between each of them: -- -- * DynFlags.sigOf is global per invocation of GHC. If we are compiling -- with --make, there may be multiple signature files being compiled; in -- which case this parameter is a map from local module name to implementing -- Module. -- -- * HscEnv.tcg_sig_of is global per the compilation of a single file, so -- it is simply the result of looking up tcg_mod in the DynFlags.sigOf -- parameter. It's setup in TcRnMonad.initTc. This prevents us -- from having to repeatedly do a lookup in DynFlags.sigOf. -- -- * HscEnv.tcg_impl_rdr_env is a RdrEnv that lets us look up names -- according to the sig-of module. It's setup in TcRnDriver.tcRnSignature. -- Here is an example showing why we need this map: -- -- module A where -- a = True -- -- module ASig where -- import B -- a :: Bool -- -- module B where -- b = False -- -- When we compile ASig --sig-of main:A, the default -- global RdrEnv (tcg_rdr_env) has an entry for b, but not for a -- (we never imported A). So we have to look in a different environment -- to actually get the original name. -- -- By the way, why do we need to do the lookup; can't we just use A:a -- as the name directly? Well, if A is reexporting the entity from another -- module, then the original name needs to be the real original name: -- -- module C where -- a = True -- -- module A(a) where -- import C instance ContainsModule TcGblEnv where extractModule env = tcg_mod env type RecFieldEnv = NameEnv [FieldLabel] -- Maps a constructor name *in this module* -- to the fields for that constructor. -- This is used when dealing with ".." notation in record -- construction and pattern matching. -- The FieldEnv deals *only* with constructors defined in *this* -- module. For imported modules, we get the same info from the -- TypeEnv data SelfBootInfo = NoSelfBoot -- No corresponding hi-boot file | SelfBoot { sb_mds :: ModDetails -- There was a hi-boot file, , sb_tcs :: NameSet -- defining these TyCons, , sb_ids :: NameSet } -- and these Ids -- We need this info to compute a safe approximation to -- recursive loops, to avoid infinite inlinings {- Note [Tracking unused binding and imports] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We gather two sorts of usage information * tcg_dus (defs/uses) Records *defined* Names (local, top-level) and *used* Names (local or imported) Used (a) to report "defined but not used" (see RnNames.reportUnusedNames) (b) to generate version-tracking usage info in interface files (see MkIface.mkUsedNames) This usage info is mainly gathered by the renamer's gathering of free-variables * tcg_used_gres Used only to report unused import declarations Records each *occurrence* an *imported* (not locally-defined) entity. The occurrence is recorded by keeping a GlobalRdrElt for it. These is not the GRE that is in the GlobalRdrEnv; rather it is recorded *after* the filtering done by pickGREs. So it reflect /how that occurrence is in scope/. See Note [GRE filtering] in RdrName. ************************************************************************ * * The local typechecker environment * * ************************************************************************ Note [The Global-Env/Local-Env story] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ During type checking, we keep in the tcg_type_env * All types and classes * All Ids derived from types and classes (constructors, selectors) At the end of type checking, we zonk the local bindings, and as we do so we add to the tcg_type_env * Locally defined top-level Ids Why? Because they are now Ids not TcIds. This final GlobalEnv is a) fed back (via the knot) to typechecking the unfoldings of interface signatures b) used in the ModDetails of this module -} data TcLclEnv -- Changes as we move inside an expression -- Discarded after typecheck/rename; not passed on to desugarer = TcLclEnv { tcl_loc :: RealSrcSpan, -- Source span tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top tcl_tclvl :: TcLevel, -- Birthplace for new unification variables tcl_th_ctxt :: ThStage, -- Template Haskell context tcl_th_bndrs :: ThBindEnv, -- Binding level of in-scope Names -- defined in this module (not imported) tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context tcl_rdr :: LocalRdrEnv, -- Local name envt -- Maintained during renaming, of course, but also during -- type checking, solely so that when renaming a Template-Haskell -- splice we have the right environment for the renamer. -- -- Does *not* include global name envt; may shadow it -- Includes both ordinary variables and type variables; -- they are kept distinct because tyvar have a different -- occurrence contructor (Name.TvOcc) -- We still need the unsullied global name env so that -- we can look up record field names tcl_env :: TcTypeEnv, -- The local type environment: -- Ids and TyVars defined in this module tcl_bndrs :: TcIdBinderStack, -- Used for reporting relevant bindings tcl_tidy :: TidyEnv, -- Used for tidying types; contains all -- in-scope type variables (but not term variables) tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars" -- Namely, the in-scope TyVars bound in tcl_env, -- plus the tyvars mentioned in the types of Ids bound -- in tcl_lenv. -- Why mutable? see notes with tcGetGlobalTyCoVars tcl_lie :: TcRef WantedConstraints, -- Place to accumulate type constraints tcl_errs :: TcRef Messages -- Place to accumulate errors } type TcTypeEnv = NameEnv TcTyThing type ThBindEnv = NameEnv (TopLevelFlag, ThLevel) -- Domain = all Ids bound in this module (ie not imported) -- The TopLevelFlag tells if the binding is syntactically top level. -- We need to know this, because the cross-stage persistence story allows -- cross-stage at arbitrary types if the Id is bound at top level. -- -- Nota bene: a ThLevel of 'outerLevel' is *not* the same as being -- bound at top level! See Note [Template Haskell levels] in TcSplice {- Note [Given Insts] ~~~~~~~~~~~~~~~~~~ Because of GADTs, we have to pass inwards the Insts provided by type signatures and existential contexts. Consider data T a where { T1 :: b -> b -> T [b] } f :: Eq a => T a -> Bool f (T1 x y) = [x]==[y] The constructor T1 binds an existential variable 'b', and we need Eq [b]. Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we pass it inwards. -} -- | Type alias for 'IORef'; the convention is we'll use this for mutable -- bits of data in 'TcGblEnv' which are updated during typechecking and -- returned at the end. type TcRef a = IORef a -- ToDo: when should I refer to it as a 'TcId' instead of an 'Id'? type TcId = Id type TcIdSet = IdSet --------------------------- -- The TcIdBinderStack --------------------------- type TcIdBinderStack = [TcIdBinder] -- This is a stack of locally-bound ids, innermost on top -- Used ony in error reporting (relevantBindings in TcError) data TcIdBinder = TcIdBndr TcId TopLevelFlag -- Tells whether the bindind is syntactically top-level -- (The monomorphic Ids for a recursive group count -- as not-top-level for this purpose.) | TcIdBndr_ExpType -- Variant that allows the type to be specified as -- an ExpType Name ExpType TopLevelFlag instance Outputable TcIdBinder where ppr (TcIdBndr id top_lvl) = ppr id <> brackets (ppr top_lvl) ppr (TcIdBndr_ExpType id _ top_lvl) = ppr id <> brackets (ppr top_lvl) instance HasOccName TcIdBinder where occName (TcIdBndr id _) = (occName (idName id)) occName (TcIdBndr_ExpType name _ _) = (occName name) --------------------------- -- Template Haskell stages and levels --------------------------- data SpliceType = Typed | Untyped data ThStage -- See Note [Template Haskell state diagram] in TcSplice = Splice SpliceType -- Inside a top-level splice -- This code will be run *at compile time*; -- the result replaces the splice -- Binding level = 0 #ifdef GHCI | RunSplice (TcRef [ForeignRef (TH.Q ())]) -- Set when running a splice, i.e. NOT when renaming or typechecking the -- Haskell code for the splice. See Note [RunSplice ThLevel]. -- -- Contains a list of mod finalizers collected while executing the splice. -- -- 'addModFinalizer' inserts finalizers here, and from here they are taken -- to construct an @HsSpliced@ annotation for untyped splices. See Note -- [Delaying modFinalizers in untyped splices] in "RnSplice". -- -- For typed splices, the typechecker takes finalizers from here and -- inserts them in the list of finalizers in the global environment. -- -- See Note [Collecting modFinalizers in typed splices] in "TcSplice". #else | RunSplice () #endif | Comp -- Ordinary Haskell code -- Binding level = 1 | Brack -- Inside brackets ThStage -- Enclosing stage PendingStuff data PendingStuff = RnPendingUntyped -- Renaming the inside of an *untyped* bracket (TcRef [PendingRnSplice]) -- Pending splices in here | RnPendingTyped -- Renaming the inside of a *typed* bracket | TcPending -- Typechecking the inside of a typed bracket (TcRef [PendingTcSplice]) -- Accumulate pending splices here (TcRef WantedConstraints) -- and type constraints here topStage, topAnnStage, topSpliceStage :: ThStage topStage = Comp topAnnStage = Splice Untyped topSpliceStage = Splice Untyped instance Outputable ThStage where ppr (Splice _) = text "Splice" ppr (RunSplice _) = text "RunSplice" ppr Comp = text "Comp" ppr (Brack s _) = text "Brack" <> parens (ppr s) type ThLevel = Int -- NB: see Note [Template Haskell levels] in TcSplice -- Incremented when going inside a bracket, -- decremented when going inside a splice -- NB: ThLevel is one greater than the 'n' in Fig 2 of the -- original "Template meta-programming for Haskell" paper impLevel, outerLevel :: ThLevel impLevel = 0 -- Imported things; they can be used inside a top level splice outerLevel = 1 -- Things defined outside brackets thLevel :: ThStage -> ThLevel thLevel (Splice _) = 0 thLevel (RunSplice _) = -- See Note [RunSplice ThLevel]. panic "thLevel: called when running a splice" thLevel Comp = 1 thLevel (Brack s _) = thLevel s + 1 {- Node [RunSplice ThLevel] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'RunSplice' stage is set when executing a splice, and only when running a splice. In particular it is not set when the splice is renamed or typechecked. 'RunSplice' is needed to provide a reference where 'addModFinalizer' can insert the finalizer (see Note [Delaying modFinalizers in untyped splices]), and 'addModFinalizer' runs when doing Q things. Therefore, It doesn't make sense to set 'RunSplice' when renaming or typechecking the splice, where 'Splice', 'Brak' or 'Comp' are used instead. -} --------------------------- -- Arrow-notation context --------------------------- {- Note [Escaping the arrow scope] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In arrow notation, a variable bound by a proc (or enclosed let/kappa) is not in scope to the left of an arrow tail (-<) or the head of (|..|). For example proc x -> (e1 -< e2) Here, x is not in scope in e1, but it is in scope in e2. This can get a bit complicated: let x = 3 in proc y -> (proc z -> e1) -< e2 Here, x and z are in scope in e1, but y is not. We implement this by recording the environment when passing a proc (using newArrowScope), and returning to that (using escapeArrowScope) on the left of -< and the head of (|..|). All this can be dealt with by the *renamer*. But the type checker needs to be involved too. Example (arrowfail001) class Foo a where foo :: a -> () data Bar = forall a. Foo a => Bar a get :: Bar -> () get = proc x -> case x of Bar a -> foo -< a Here the call of 'foo' gives rise to a (Foo a) constraint that should not be captured by the pattern match on 'Bar'. Rather it should join the constraints from further out. So we must capture the constraint bag from further out in the ArrowCtxt that we push inwards. -} data ArrowCtxt -- Note [Escaping the arrow scope] = NoArrowCtxt | ArrowCtxt LocalRdrEnv (TcRef WantedConstraints) --------------------------- -- TcTyThing --------------------------- -- | A typecheckable thing available in a local context. Could be -- 'AGlobal' 'TyThing', but also lexically scoped variables, etc. -- See 'TcEnv' for how to retrieve a 'TyThing' given a 'Name'. data TcTyThing = AGlobal TyThing -- Used only in the return type of a lookup | ATcId { -- Ids defined in this module; may not be fully zonked tct_id :: TcId, tct_closed :: TopLevelFlag } -- See Note [Bindings with closed types] | ATyVar Name TcTyVar -- The type variable to which the lexically scoped type -- variable is bound. We only need the Name -- for error-message purposes; it is the corresponding -- Name in the domain of the envt | ATcTyCon TyCon -- Used temporarily, during kind checking, for the -- tycons and clases in this recursive group -- The TyCon is always a TcTyCon. Its kind -- can be a mono-kind or a poly-kind; in TcTyClsDcls see -- Note [Type checking recursive type and class declarations] | APromotionErr PromotionErr data PromotionErr = TyConPE -- TyCon used in a kind before we are ready -- data T :: T -> * where ... | ClassPE -- Ditto Class | FamDataConPE -- Data constructor for a data family -- See Note [AFamDataCon: not promoting data family constructors] in TcRnDriver | PatSynPE -- Pattern synonyms -- See Note [Don't promote pattern synonyms] in TcEnv | RecDataConPE -- Data constructor in a recursive loop -- See Note [ARecDataCon: recusion and promoting data constructors] in TcTyClsDecls | NoDataKindsTC -- -XDataKinds not enabled (for a tycon) | NoDataKindsDC -- -XDataKinds not enabled (for a datacon) | NoTypeInTypeTC -- -XTypeInType not enabled (for a tycon) | NoTypeInTypeDC -- -XTypeInType not enabled (for a datacon) instance Outputable TcTyThing where -- Debugging only ppr (AGlobal g) = pprTyThing g ppr elt@(ATcId {}) = text "Identifier" <> brackets (ppr (tct_id elt) <> dcolon <> ppr (varType (tct_id elt)) <> comma <+> ppr (tct_closed elt)) ppr (ATyVar n tv) = text "Type variable" <+> quotes (ppr n) <+> equals <+> ppr tv ppr (ATcTyCon tc) = text "ATcTyCon" <+> ppr tc ppr (APromotionErr err) = text "APromotionErr" <+> ppr err instance Outputable PromotionErr where ppr ClassPE = text "ClassPE" ppr TyConPE = text "TyConPE" ppr PatSynPE = text "PatSynPE" ppr FamDataConPE = text "FamDataConPE" ppr RecDataConPE = text "RecDataConPE" ppr NoDataKindsTC = text "NoDataKindsTC" ppr NoDataKindsDC = text "NoDataKindsDC" ppr NoTypeInTypeTC = text "NoTypeInTypeTC" ppr NoTypeInTypeDC = text "NoTypeInTypeDC" pprTcTyThingCategory :: TcTyThing -> SDoc pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing pprTcTyThingCategory (ATyVar {}) = text "Type variable" pprTcTyThingCategory (ATcId {}) = text "Local identifier" pprTcTyThingCategory (ATcTyCon {}) = text "Local tycon" pprTcTyThingCategory (APromotionErr pe) = pprPECategory pe pprPECategory :: PromotionErr -> SDoc pprPECategory ClassPE = text "Class" pprPECategory TyConPE = text "Type constructor" pprPECategory PatSynPE = text "Pattern synonym" pprPECategory FamDataConPE = text "Data constructor" pprPECategory RecDataConPE = text "Data constructor" pprPECategory NoDataKindsTC = text "Type constructor" pprPECategory NoDataKindsDC = text "Data constructor" pprPECategory NoTypeInTypeTC = text "Type constructor" pprPECategory NoTypeInTypeDC = text "Data constructor" {- Note [Bindings with closed types] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider f x = let g ys = map not ys in ... Can we generalise 'g' under the OutsideIn algorithm? Yes, because all g's free variables are top-level; that is they themselves have no free type variables, and it is the type variables in the environment that makes things tricky for OutsideIn generalisation. Definition: A variable is "closed", and has tct_closed set to TopLevel, iff a) all its free variables are imported, or are let-bound with closed types b) generalisation is not restricted by the monomorphism restriction Invariant: a closed variable has no free type variables in its type. Under OutsideIn we are free to generalise a closed let-binding. This is an extension compared to the JFP paper on OutsideIn, which used "top-level" as a proxy for "closed". (It's not a good proxy anyway -- the MR can make a top-level binding with a free type variable.) Note that: * A top-level binding may not be closed, if it suffers from the MR * A nested binding may be closed (eg 'g' in the example we started with) Indeed, that's the point; whether a function is defined at top level or nested is orthogonal to the question of whether or not it is closed * A binding may be non-closed because it mentions a lexically scoped *type variable* Eg f :: forall a. blah f x = let g y = ...(y::a)... -} type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, MsgDoc)) -- Monadic so that we have a chance -- to deal with bound type variables just before error -- message construction -- Bool: True <=> this is a landmark context; do not -- discard it when trimming for display {- ************************************************************************ * * Operations over ImportAvails * * ************************************************************************ -} -- | 'ImportAvails' summarises what was imported from where, irrespective of -- whether the imported things are actually used or not. It is used: -- -- * when processing the export list, -- -- * when constructing usage info for the interface file, -- -- * to identify the list of directly imported modules for initialisation -- purposes and for optimised overlap checking of family instances, -- -- * when figuring out what things are really unused -- data ImportAvails = ImportAvails { imp_mods :: ImportedMods, -- = ModuleEnv [ImportedModsVal], -- ^ Domain is all directly-imported modules -- -- See the documentaion on ImportedModsVal in HscTypes for the -- meaning of the fields. -- -- We need a full ModuleEnv rather than a ModuleNameEnv here, -- because we might be importing modules of the same name from -- different packages. (currently not the case, but might be in the -- future). imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface), -- ^ Home-package modules needed by the module being compiled -- -- It doesn't matter whether any of these dependencies -- are actually /used/ when compiling the module; they -- are listed if they are below it at all. For -- example, suppose M imports A which imports X. Then -- compiling M might not need to consult X.hi, but X -- is still listed in M's dependencies. imp_dep_pkgs :: [UnitId], -- ^ Packages needed by the module being compiled, whether directly, -- or via other modules in this package, or via modules imported -- from other packages. imp_trust_pkgs :: [UnitId], -- ^ This is strictly a subset of imp_dep_pkgs and records the -- packages the current module needs to trust for Safe Haskell -- compilation to succeed. A package is required to be trusted if -- we are dependent on a trustworthy module in that package. -- While perhaps making imp_dep_pkgs a tuple of (UnitId, Bool) -- where True for the bool indicates the package is required to be -- trusted is the more logical design, doing so complicates a lot -- of code not concerned with Safe Haskell. -- See Note [RnNames . Tracking Trust Transitively] imp_trust_own_pkg :: Bool, -- ^ Do we require that our own package is trusted? -- This is to handle efficiently the case where a Safe module imports -- a Trustworthy module that resides in the same package as it. -- See Note [RnNames . Trust Own Package] imp_orphs :: [Module], -- ^ Orphan modules below us in the import tree (and maybe including -- us for imported modules) imp_finsts :: [Module] -- ^ Family instance modules below us in the import tree (and maybe -- including us for imported modules) } mkModDeps :: [(ModuleName, IsBootInterface)] -> ModuleNameEnv (ModuleName, IsBootInterface) mkModDeps deps = foldl add emptyUFM deps where add env elt@(m,_) = addToUFM env m elt emptyImportAvails :: ImportAvails emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv, imp_dep_mods = emptyUFM, imp_dep_pkgs = [], imp_trust_pkgs = [], imp_trust_own_pkg = False, imp_orphs = [], imp_finsts = [] } -- | Union two ImportAvails -- -- This function is a key part of Import handling, basically -- for each import we create a separate ImportAvails structure -- and then union them all together with this function. plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails plusImportAvails (ImportAvails { imp_mods = mods1, imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1, imp_trust_pkgs = tpkgs1, imp_trust_own_pkg = tself1, imp_orphs = orphs1, imp_finsts = finsts1 }) (ImportAvails { imp_mods = mods2, imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2, imp_trust_pkgs = tpkgs2, imp_trust_own_pkg = tself2, imp_orphs = orphs2, imp_finsts = finsts2 }) = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2, imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2, imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2, imp_trust_pkgs = tpkgs1 `unionLists` tpkgs2, imp_trust_own_pkg = tself1 || tself2, imp_orphs = orphs1 `unionLists` orphs2, imp_finsts = finsts1 `unionLists` finsts2 } where plus_mod_dep (m1, boot1) (m2, boot2) = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) ) -- Check mod-names match (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that {- ************************************************************************ * * \subsection{Where from} * * ************************************************************************ The @WhereFrom@ type controls where the renamer looks for an interface file -} data WhereFrom = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-}) | ImportBySystem -- Non user import. | ImportByPlugin -- Importing a plugin; -- See Note [Care with plugin imports] in LoadIface instance Outputable WhereFrom where ppr (ImportByUser is_boot) | is_boot = text "{- SOURCE -}" | otherwise = empty ppr ImportBySystem = text "{- SYSTEM -}" ppr ImportByPlugin = text "{- PLUGIN -}" {- ********************************************************************* * * Type signatures * * ********************************************************************* -} type TcSigFun = Name -> Maybe TcSigInfo data TcSigInfo = TcIdSig TcIdSigInfo | TcPatSynSig TcPatSynInfo data TcIdSigInfo = TISI { sig_bndr :: TcIdSigBndr , sig_skols :: [(Name, TcTyVar)] -- Instantiated type and kind variables SKOLEMS -- The Name is the Name that the renamer chose; -- but the TcTyVar may come from instantiating -- the type and hence have a different unique. -- No need to keep track of whether they are truly lexically -- scoped because the renamer has named them uniquely -- -- For Partial signatures, this list /excludes/ any wildcards -- the named wildcards scope over the binding, and hence -- their Names may appear in renamed type signatures -- in the binding; get them from sig_bndr -- See Note [Binding scoped type variables] , sig_theta :: TcThetaType -- Instantiated theta. In the case of a -- PartialSig, sig_theta does not include -- the extra-constraints wildcard , sig_tau :: TcSigmaType -- Instantiated tau -- See Note [sig_tau may be polymorphic] , sig_ctxt :: UserTypeCtxt -- In the case of type-class default methods, -- the Name in the FunSigCtxt is not the same -- as the TcId; the former is 'op', while the -- latter is '$dmop' or some such , sig_loc :: SrcSpan -- Location of the type signature } data TcIdSigBndr -- See Note [Complete and partial type signatures] = CompleteSig -- A complete signature with no wildcards, -- so the complete polymorphic type is known. TcId -- The polymorphic Id with that type | PartialSig -- A partial type signature (i.e. includes one or more -- wildcards). In this case it doesn't make sense to give -- the polymorphic Id, because we are going to /infer/ its -- type, so we can't make the polymorphic Id ab-initio { sig_name :: Name -- Name of the function; used when report wildcards , sig_hs_ty :: LHsType Name -- The original partial signature , sig_wcs :: [(Name,TcTyVar)] -- Instantiated wildcard variables (named and anonymous) -- The Name is what the user wrote, such as '_', -- including SrcSpan for the error message; -- The TcTyVar is just an ordinary unification variable , sig_cts :: Maybe SrcSpan -- Just loc <=> An extra-constraints wildcard was present } -- at location loc -- e.g. f :: (Eq a, _) => a -> a data TcPatSynInfo = TPSI { patsig_name :: Name, patsig_univ_bndrs :: [TcTyBinder], patsig_req :: TcThetaType, patsig_ex_bndrs :: [TcTyBinder], patsig_prov :: TcThetaType, patsig_arg_tys :: [TcSigmaType], patsig_body_ty :: TcSigmaType } findScopedTyVars -- See Note [Binding scoped type variables] :: TcType -- The Type: its forall'd variables are a superset -- of the lexically scoped variables -> [TcTyVar] -- The instantiated forall variables of the TcType -> [(Name, TcTyVar)] -- In 1-1 correspondence with the instantiated vars findScopedTyVars sig_ty inst_tvs = zipWith find sig_tvs inst_tvs where find sig_tv inst_tv = (tyVarName sig_tv, inst_tv) (sig_tvs,_) = tcSplitForAllTys sig_ty instance Outputable TcSigInfo where ppr (TcIdSig idsi) = ppr idsi ppr (TcPatSynSig tpsi) = text "TcPatSynInfo" <+> ppr tpsi instance Outputable TcIdSigInfo where ppr (TISI { sig_bndr = bndr, sig_skols = tyvars , sig_theta = theta, sig_tau = tau }) = ppr (tcIdSigBndrName bndr) <+> dcolon <+> vcat [ pprSigmaType (mkSpecSigmaTy (map snd tyvars) theta tau) , ppr (map fst tyvars) ] instance Outputable TcIdSigBndr where ppr (CompleteSig f) = text "CompleteSig" <+> ppr f ppr (PartialSig { sig_name = n }) = text "PartialSig" <+> ppr n instance Outputable TcPatSynInfo where ppr (TPSI{ patsig_name = name}) = ppr name isPartialSig :: TcIdSigInfo -> Bool isPartialSig (TISI { sig_bndr = PartialSig {} }) = True isPartialSig _ = False -- | No signature or a partial signature noCompleteSig :: Maybe TcSigInfo -> Bool noCompleteSig (Just (TcIdSig sig)) = isPartialSig sig noCompleteSig _ = True tcIdSigBndrName :: TcIdSigBndr -> Name tcIdSigBndrName (CompleteSig id) = idName id tcIdSigBndrName (PartialSig { sig_name = n }) = n tcSigInfoName :: TcSigInfo -> Name tcSigInfoName (TcIdSig idsi) = tcIdSigBndrName (sig_bndr idsi) tcSigInfoName (TcPatSynSig tpsi) = patsig_name tpsi -- Helper for cases when we know for sure we have a complete type -- signature, e.g. class methods. completeIdSigPolyId :: TcIdSigInfo -> TcId completeIdSigPolyId (TISI { sig_bndr = CompleteSig id }) = id completeIdSigPolyId _ = panic "completeSigPolyId" completeIdSigPolyId_maybe :: TcIdSigInfo -> Maybe TcId completeIdSigPolyId_maybe (TISI { sig_bndr = CompleteSig id }) = Just id completeIdSigPolyId_maybe _ = Nothing completeSigPolyId_maybe :: TcSigInfo -> Maybe TcId completeSigPolyId_maybe (TcIdSig sig) = completeIdSigPolyId_maybe sig completeSigPolyId_maybe (TcPatSynSig {}) = Nothing {- Note [Binding scoped type variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The type variables *brought into lexical scope* by a type signature may be a subset of the *quantified type variables* of the signatures, for two reasons: * With kind polymorphism a signature like f :: forall f a. f a -> f a may actually give rise to f :: forall k. forall (f::k -> *) (a:k). f a -> f a So the sig_tvs will be [k,f,a], but only f,a are scoped. NB: the scoped ones are not necessarily the *inital* ones! * Even aside from kind polymorphism, there may be more instantiated type variables than lexically-scoped ones. For example: type T a = forall b. b -> (a,b) f :: forall c. T c Here, the signature for f will have one scoped type variable, c, but two instantiated type variables, c' and b'. The function findScopedTyVars takes * hs_ty: the original HsForAllTy * sig_ty: the corresponding Type (which is guaranteed to use the same Names as the HsForAllTy) * inst_tvs: the skolems instantiated from the forall's in sig_ty It returns a [(Maybe Name, TcTyVar)], in 1-1 correspondence with inst_tvs but with a (Just n) for the lexically scoped name of each in-scope tyvar. Note [sig_tau may be polymorphic] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Note that "sig_tau" might actually be a polymorphic type, if the original function had a signature like forall a. Eq a => forall b. Ord b => .... But that's ok: tcMatchesFun (called by tcRhs) can deal with that It happens, too! See Note [Polymorphic methods] in TcClassDcl. Note [Existential check] ~~~~~~~~~~~~~~~~~~~~~~~~ Lazy patterns can't bind existentials. They arise in two ways: * Let bindings let { C a b = e } in b * Twiddle patterns f ~(C a b) = e The pe_lazy field of PatEnv says whether we are inside a lazy pattern (perhaps deeply) If we aren't inside a lazy pattern then we can bind existentials, but we need to be careful about "extra" tyvars. Consider (\C x -> d) : pat_ty -> res_ty When looking for existential escape we must check that the existential bound by C don't unify with the free variables of pat_ty, OR res_ty (or of course the environment). Hence we need to keep track of the res_ty free vars. Note [Complete and partial type signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A type signature is partial when it contains one or more wildcards (= type holes). The wildcard can either be: * A (type) wildcard occurring in sig_theta or sig_tau. These are stored in sig_wcs. f :: Bool -> _ g :: Eq _a => _a -> _a -> Bool * Or an extra-constraints wildcard, stored in sig_cts: h :: (Num a, _) => a -> a A type signature is a complete type signature when there are no wildcards in the type signature, i.e. iff sig_wcs is empty and sig_extra_cts is Nothing. -} {- ************************************************************************ * * * Canonical constraints * * * * These are the constraints the low-level simplifier works with * * * ************************************************************************ -} -- The syntax of xi types: -- xi ::= a | T xis | xis -> xis | ... | forall a. tau -- Two important notes: -- (i) No type families, unless we are under a ForAll -- (ii) Note that xi types can contain unexpanded type synonyms; -- however, the (transitive) expansions of those type synonyms -- will not contain any type functions, unless we are under a ForAll. -- We enforce the structure of Xi types when we flatten (TcCanonical) type Xi = Type -- In many comments, "xi" ranges over Xi type Cts = Bag Ct data Ct -- Atomic canonical constraints = CDictCan { -- e.g. Num xi cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant] cc_class :: Class, cc_tyargs :: [Xi], -- cc_tyargs are function-free, hence Xi cc_pend_sc :: Bool -- True <=> (a) cc_class has superclasses -- (b) we have not (yet) added those -- superclasses as Givens -- NB: cc_pend_sc is used for G/W/D. For W/D the reason -- we need superclasses is to expose possible improvement -- via fundeps } | CIrredEvCan { -- These stand for yet-unusable predicates cc_ev :: CtEvidence -- See Note [Ct/evidence invariant] -- The ctev_pred of the evidence is -- of form (tv xi1 xi2 ... xin) -- or (tv1 ~ ty2) where the CTyEqCan kind invariant fails -- or (F tys ~ ty) where the CFunEqCan kind invariant fails -- See Note [CIrredEvCan constraints] } | CTyEqCan { -- tv ~ rhs -- Invariants: -- * See Note [Applying the inert substitution] in TcFlatten -- * tv not in tvs(rhs) (occurs check) -- * If tv is a TauTv, then rhs has no foralls -- (this avoids substituting a forall for the tyvar in other types) -- * typeKind ty `tcEqKind` typeKind tv -- * rhs may have at most one top-level cast -- * rhs (perhaps under the one cast) is not necessarily function-free, -- but it has no top-level function. -- E.g. a ~ [F b] is fine -- but a ~ F b is not -- * If the equality is representational, rhs has no top-level newtype -- See Note [No top-level newtypes on RHS of representational -- equalities] in TcCanonical -- * If rhs (perhaps under the cast) is also a tv, then it is oriented -- to give best chance of -- unification happening; eg if rhs is touchable then lhs is too cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant] cc_tyvar :: TcTyVar, cc_rhs :: TcType, -- Not necessarily function-free (hence not Xi) -- See invariants above cc_eq_rel :: EqRel } | CFunEqCan { -- F xis ~ fsk -- Invariants: -- * isTypeFamilyTyCon cc_fun -- * typeKind (F xis) = tyVarKind fsk -- * always Nominal role cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant] cc_fun :: TyCon, -- A type function cc_tyargs :: [Xi], -- cc_tyargs are function-free (hence Xi) -- Either under-saturated or exactly saturated -- *never* over-saturated (because if so -- we should have decomposed) cc_fsk :: TcTyVar -- [Given] always a FlatSkol skolem -- [Wanted] always a FlatMetaTv unification variable -- See Note [The flattening story] in TcFlatten } | CNonCanonical { -- See Note [NonCanonical Semantics] in TcSMonad cc_ev :: CtEvidence } | CHoleCan { -- See Note [Hole constraints] -- Treated as an "insoluble" constraint -- See Note [Insoluble constraints] cc_ev :: CtEvidence, cc_hole :: Hole } -- | An expression or type hole data Hole = ExprHole UnboundVar -- ^ Either an out-of-scope variable or a "true" hole in an -- expression (TypedHoles) | TypeHole OccName -- ^ A hole in a type (PartialTypeSignatures) holeOcc :: Hole -> OccName holeOcc (ExprHole uv) = unboundVarOcc uv holeOcc (TypeHole occ) = occ {- Note [Hole constraints] ~~~~~~~~~~~~~~~~~~~~~~~ CHoleCan constraints are used for two kinds of holes, distinguished by cc_hole: * For holes in expressions (including variables not in scope) e.g. f x = g _ x * For holes in type signatures e.g. f :: _ -> _ f x = [x,True] Note [CIrredEvCan constraints] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CIrredEvCan constraints are used for constraints that are "stuck" - we can't solve them (yet) - we can't use them to solve other constraints - but they may become soluble if we substitute for some of the type variables in the constraint Example 1: (c Int), where c :: * -> Constraint. We can't do anything with this yet, but if later c := Num, *then* we can solve it Example 2: a ~ b, where a :: *, b :: k, where k is a kind variable We don't want to use this to substitute 'b' for 'a', in case 'k' is subequently unifed with (say) *->*, because then we'd have ill-kinded types floating about. Rather we want to defer using the equality altogether until 'k' get resolved. Note [Ct/evidence invariant] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If ct :: Ct, then extra fields of 'ct' cache precisely the ctev_pred field of (cc_ev ct), and is fully rewritten wrt the substitution. Eg for CDictCan, ctev_pred (cc_ev ct) = (cc_class ct) (cc_tyargs ct) This holds by construction; look at the unique place where CDictCan is built (in TcCanonical). In contrast, the type of the evidence *term* (ccev_evtm or ctev_evar/dest) in the evidence may *not* be fully zonked; we are careful not to look at it during constraint solving. See Note [Evidence field of CtEvidence] -} mkNonCanonical :: CtEvidence -> Ct mkNonCanonical ev = CNonCanonical { cc_ev = ev } mkNonCanonicalCt :: Ct -> Ct mkNonCanonicalCt ct = CNonCanonical { cc_ev = cc_ev ct } mkGivens :: CtLoc -> [EvId] -> [Ct] mkGivens loc ev_ids = map mk ev_ids where mk ev_id = mkNonCanonical (CtGiven { ctev_evar = ev_id , ctev_pred = evVarPred ev_id , ctev_loc = loc }) ctEvidence :: Ct -> CtEvidence ctEvidence = cc_ev ctLoc :: Ct -> CtLoc ctLoc = ctEvLoc . ctEvidence setCtLoc :: Ct -> CtLoc -> Ct setCtLoc ct loc = ct { cc_ev = (cc_ev ct) { ctev_loc = loc } } ctOrigin :: Ct -> CtOrigin ctOrigin = ctLocOrigin . ctLoc ctPred :: Ct -> PredType -- See Note [Ct/evidence invariant] ctPred ct = ctEvPred (cc_ev ct) -- | Convert a Wanted to a Derived toDerivedCt :: Ct -> Ct toDerivedCt ct = case ctEvidence ct of CtWanted { ctev_pred = pred, ctev_loc = loc } -> ct {cc_ev = CtDerived {ctev_pred = pred, ctev_loc = loc}} CtDerived {} -> ct CtGiven {} -> pprPanic "to_derived" (ppr ct) -- | Makes a new equality predicate with the same role as the given -- evidence. mkTcEqPredLikeEv :: CtEvidence -> TcType -> TcType -> TcType mkTcEqPredLikeEv ev = case predTypeEqRel pred of NomEq -> mkPrimEqPred ReprEq -> mkReprPrimEqPred where pred = ctEvPred ev -- | Get the flavour of the given 'Ct' ctFlavour :: Ct -> CtFlavour ctFlavour = ctEvFlavour . ctEvidence -- | Get the equality relation for the given 'Ct' ctEqRel :: Ct -> EqRel ctEqRel = ctEvEqRel . ctEvidence instance Outputable Ct where ppr ct = ppr (cc_ev ct) <+> parens pp_sort where pp_sort = case ct of CTyEqCan {} -> text "CTyEqCan" CFunEqCan {} -> text "CFunEqCan" CNonCanonical {} -> text "CNonCanonical" CDictCan { cc_pend_sc = pend_sc } | pend_sc -> text "CDictCan(psc)" | otherwise -> text "CDictCan" CIrredEvCan {} -> text "CIrredEvCan" CHoleCan { cc_hole = hole } -> text "CHoleCan:" <+> ppr (holeOcc hole) {- ************************************************************************ * * Simple functions over evidence variables * * ************************************************************************ -} ---------------- Getting free tyvars ------------------------- -- | Returns free variables of constraints as a non-deterministic set tyCoVarsOfCt :: Ct -> TcTyCoVarSet tyCoVarsOfCt = fvVarSet . tyCoFVsOfCt -- | Returns free variables of constraints as a deterministically ordered. -- list. See Note [Deterministic FV] in FV. tyCoVarsOfCtList :: Ct -> [TcTyCoVar] tyCoVarsOfCtList = fvVarList . tyCoFVsOfCt -- | Returns free variables of constraints as a composable FV computation. -- See Note [Deterministic FV] in FV. tyCoFVsOfCt :: Ct -> FV tyCoFVsOfCt (CTyEqCan { cc_tyvar = tv, cc_rhs = xi }) = tyCoFVsOfType xi `unionFV` FV.unitFV tv `unionFV` tyCoFVsOfType (tyVarKind tv) tyCoFVsOfCt (CFunEqCan { cc_tyargs = tys, cc_fsk = fsk }) = tyCoFVsOfTypes tys `unionFV` FV.unitFV fsk `unionFV` tyCoFVsOfType (tyVarKind fsk) tyCoFVsOfCt (CDictCan { cc_tyargs = tys }) = tyCoFVsOfTypes tys tyCoFVsOfCt (CIrredEvCan { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev) tyCoFVsOfCt (CHoleCan { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev) tyCoFVsOfCt (CNonCanonical { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev) -- | Returns free variables of a bag of constraints as a non-deterministic -- set. See Note [Deterministic FV] in FV. tyCoVarsOfCts :: Cts -> TcTyCoVarSet tyCoVarsOfCts = fvVarSet . tyCoFVsOfCts -- | Returns free variables of a bag of constraints as a deterministically -- odered list. See Note [Deterministic FV] in FV. tyCoVarsOfCtsList :: Cts -> [TcTyCoVar] tyCoVarsOfCtsList = fvVarList . tyCoFVsOfCts -- | Returns free variables of a bag of constraints as a composable FV -- computation. See Note [Deterministic FV] in FV. tyCoFVsOfCts :: Cts -> FV tyCoFVsOfCts = foldrBag (unionFV . tyCoFVsOfCt) emptyFV -- | Returns free variables of WantedConstraints as a non-deterministic -- set. See Note [Deterministic FV] in FV. tyCoVarsOfWC :: WantedConstraints -> TyCoVarSet -- Only called on *zonked* things, hence no need to worry about flatten-skolems tyCoVarsOfWC = fvVarSet . tyCoFVsOfWC -- | Returns free variables of WantedConstraints as a deterministically -- ordered list. See Note [Deterministic FV] in FV. tyCoVarsOfWCList :: WantedConstraints -> [TyCoVar] -- Only called on *zonked* things, hence no need to worry about flatten-skolems tyCoVarsOfWCList = fvVarList . tyCoFVsOfWC -- | Returns free variables of WantedConstraints as a composable FV -- computation. See Note [Deterministic FV] in FV. tyCoFVsOfWC :: WantedConstraints -> FV -- Only called on *zonked* things, hence no need to worry about flatten-skolems tyCoFVsOfWC (WC { wc_simple = simple, wc_impl = implic, wc_insol = insol }) = tyCoFVsOfCts simple `unionFV` tyCoFVsOfBag tyCoFVsOfImplic implic `unionFV` tyCoFVsOfCts insol -- | Returns free variables of Implication as a composable FV computation. -- See Note [Deterministic FV] in FV. tyCoFVsOfImplic :: Implication -> FV -- Only called on *zonked* things, hence no need to worry about flatten-skolems tyCoFVsOfImplic (Implic { ic_skols = skols , ic_given = givens, ic_wanted = wanted }) = FV.delFVs (mkVarSet skols) (tyCoFVsOfWC wanted `unionFV` tyCoFVsOfTypes (map evVarPred givens)) tyCoFVsOfBag :: (a -> FV) -> Bag a -> FV tyCoFVsOfBag tvs_of = foldrBag (unionFV . tvs_of) emptyFV -------------------------- dropDerivedSimples :: Cts -> Cts dropDerivedSimples simples = filterBag isWantedCt simples -- simples are all Wanted or Derived dropDerivedInsols :: Cts -> Cts -- See Note [Dropping derived constraints] dropDerivedInsols insols = filterBag keep insols where -- insols can include Given keep ct | isDerivedCt ct = not (isDroppableDerivedLoc (ctLoc ct)) | otherwise = True isDroppableDerivedLoc :: CtLoc -> Bool -- Note [Dropping derived constraints] isDroppableDerivedLoc loc = case ctLocOrigin loc of HoleOrigin {} -> False KindEqOrigin {} -> False GivenOrigin {} -> False FunDepOrigin1 {} -> False FunDepOrigin2 {} -> False _ -> True arisesFromGivens :: Ct -> Bool arisesFromGivens ct = case ctEvidence ct of CtGiven {} -> True CtWanted {} -> False CtDerived { ctev_loc = loc } -> from_given loc where from_given :: CtLoc -> Bool from_given loc = from_given_origin (ctLocOrigin loc) from_given_origin :: CtOrigin -> Bool from_given_origin (GivenOrigin {}) = True from_given_origin (FunDepOrigin1 _ l1 _ l2) = from_given l1 && from_given l2 from_given_origin (FunDepOrigin2 _ o1 _ _) = from_given_origin o1 from_given_origin _ = False {- Note [Dropping derived constraints] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In general we discard derived constraints at the end of constraint solving; see dropDerivedWC. For example * If we have an unsolved [W] (Ord a), we don't want to complain about an unsolved [D] (Eq a) as well. * If we have [W] a ~ Int, [W] a ~ Bool, improvement will generate [D] Int ~ Bool, and we don't want to report that because it's incomprehensible. That is why we don't rewrite wanteds with wanteds! But (tiresomely) we do keep *some* Derived insolubles: * Insoluble kind equalities (e.g. [D] * ~ (* -> *)) may arise from a type equality a ~ Int#, say. In future they'll be Wanted, not Derived, but at the moment they are Derived. * Insoluble derived equalities (e.g. [D] Int ~ Bool) may arise from functional dependency interactions, either between Givens or Wanteds. It seems sensible to retain these: - For Givens they reflect unreachable code - For Wanteds it is arguably better to get a fundep error than a no-instance error (Trac #9612) * Type holes are derived constraints because they have no evidence and we want to keep them so we get the error report Moreover, we keep *all* derived insolubles under some circumstances: * They are looked at by simplifyInfer, to decide whether to generalise. Example: [W] a ~ Int, [W] a ~ Bool We get [D] Int ~ Bool, and indeed the constraints are insoluble, and we want simplifyInfer to see that, even though we don't ultimately want to generate an (inexplicable) error message from To distinguish these cases we use the CtOrigin. ************************************************************************ * * CtEvidence The "flavor" of a canonical constraint * * ************************************************************************ -} isWantedCt :: Ct -> Bool isWantedCt = isWanted . cc_ev isGivenCt :: Ct -> Bool isGivenCt = isGiven . cc_ev isDerivedCt :: Ct -> Bool isDerivedCt = isDerived . cc_ev isCTyEqCan :: Ct -> Bool isCTyEqCan (CTyEqCan {}) = True isCTyEqCan (CFunEqCan {}) = False isCTyEqCan _ = False isCDictCan_Maybe :: Ct -> Maybe Class isCDictCan_Maybe (CDictCan {cc_class = cls }) = Just cls isCDictCan_Maybe _ = Nothing isCIrredEvCan :: Ct -> Bool isCIrredEvCan (CIrredEvCan {}) = True isCIrredEvCan _ = False isCFunEqCan_maybe :: Ct -> Maybe (TyCon, [Type]) isCFunEqCan_maybe (CFunEqCan { cc_fun = tc, cc_tyargs = xis }) = Just (tc, xis) isCFunEqCan_maybe _ = Nothing isCFunEqCan :: Ct -> Bool isCFunEqCan (CFunEqCan {}) = True isCFunEqCan _ = False isCNonCanonical :: Ct -> Bool isCNonCanonical (CNonCanonical {}) = True isCNonCanonical _ = False isHoleCt:: Ct -> Bool isHoleCt (CHoleCan {}) = True isHoleCt _ = False isOutOfScopeCt :: Ct -> Bool -- We treat expression holes representing out-of-scope variables a bit -- differently when it comes to error reporting isOutOfScopeCt (CHoleCan { cc_hole = ExprHole (OutOfScope {}) }) = True isOutOfScopeCt _ = False isExprHoleCt :: Ct -> Bool isExprHoleCt (CHoleCan { cc_hole = ExprHole {} }) = True isExprHoleCt _ = False isTypeHoleCt :: Ct -> Bool isTypeHoleCt (CHoleCan { cc_hole = TypeHole {} }) = True isTypeHoleCt _ = False {- Note [Custom type errors in constraints] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When GHC reports a type-error about an unsolved-constraint, we check to see if the constraint contains any custom-type errors, and if so we report them. Here are some examples of constraints containing type errors: TypeError msg -- The actual constraint is a type error TypError msg ~ Int -- Some type was supposed to be Int, but ended up -- being a type error instead Eq (TypeError msg) -- A class constraint is stuck due to a type error F (TypeError msg) ~ a -- A type function failed to evaluate due to a type err It is also possible to have constraints where the type error is nested deeper, for example see #11990, and also: Eq (F (TypeError msg)) -- Here the type error is nested under a type-function -- call, which failed to evaluate because of it, -- and so the `Eq` constraint was unsolved. -- This may happen when one function calls another -- and the called function produced a custom type error. -} -- | A constraint is considered to be a custom type error, if it contains -- custom type errors anywhere in it. -- See Note [Custom type errors in constraints] getUserTypeErrorMsg :: Ct -> Maybe Type getUserTypeErrorMsg ct = findUserTypeError (ctPred ct) where findUserTypeError t = msum ( userTypeError_maybe t : map findUserTypeError (subTys t) ) subTys t = case splitAppTys t of (t,[]) -> case splitTyConApp_maybe t of Nothing -> [] Just (_,ts) -> ts (t,ts) -> t : ts isUserTypeErrorCt :: Ct -> Bool isUserTypeErrorCt ct = case getUserTypeErrorMsg ct of Just _ -> True _ -> False isPendingScDict :: Ct -> Maybe Ct -- Says whether cc_pend_sc is True, AND if so flips the flag isPendingScDict ct@(CDictCan { cc_pend_sc = True }) = Just (ct { cc_pend_sc = False }) isPendingScDict _ = Nothing superClassesMightHelp :: Ct -> Bool -- ^ True if taking superclasses of givens, or of wanteds (to perhaps -- expose more equalities or functional dependencies) might help to -- solve this constraint. See Note [When superclases help] superClassesMightHelp ct = isWantedCt ct && not (is_ip ct) where is_ip (CDictCan { cc_class = cls }) = isIPClass cls is_ip _ = False {- Note [When superclasses help] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ First read Note [The superclass story] in TcCanonical. We expand superclasses and iterate only if there is at unsolved wanted for which expansion of superclasses (e.g. from given constraints) might actually help. The function superClassesMightHelp tells if doing this superclass expansion might help solve this constraint. Note that * Superclasses help only for Wanted constraints. Derived constraints are not really "unsolved" and we certainly don't want them to trigger superclass expansion. This was a good part of the loop in Trac #11523 * Even for Wanted constraints, we say "no" for implicit paramters. we have [W] ?x::ty, expanding superclasses won't help: - Superclasses can't be implicit parameters - If we have a [G] ?x:ty2, then we'll have another unsolved [D] ty ~ ty2 (from the functional dependency) which will trigger superclass expansion. It's a bit of a special case, but it's easy to do. The runtime cost is low because the unsolved set is usually empty anyway (errors aside), and the first non-imlicit-parameter will terminate the search. The special case is worth it (Trac #11480, comment:2) because it applies to CallStack constraints, which aren't type errors. If we have f :: (C a) => blah f x = ...undefined... we'll get a CallStack constraint. If that's the only unsolved constraint it'll eventually be solved by defaulting. So we don't want to emit warnings about hitting the simplifier's iteration limit. A CallStack constraint really isn't an unsolved constraint; it can always be solved by defaulting. -} singleCt :: Ct -> Cts singleCt = unitBag andCts :: Cts -> Cts -> Cts andCts = unionBags listToCts :: [Ct] -> Cts listToCts = listToBag ctsElts :: Cts -> [Ct] ctsElts = bagToList consCts :: Ct -> Cts -> Cts consCts = consBag snocCts :: Cts -> Ct -> Cts snocCts = snocBag extendCtsList :: Cts -> [Ct] -> Cts extendCtsList cts xs | null xs = cts | otherwise = cts `unionBags` listToBag xs andManyCts :: [Cts] -> Cts andManyCts = unionManyBags emptyCts :: Cts emptyCts = emptyBag isEmptyCts :: Cts -> Bool isEmptyCts = isEmptyBag pprCts :: Cts -> SDoc pprCts cts = vcat (map ppr (bagToList cts)) {- ************************************************************************ * * Wanted constraints These are forced to be in TcRnTypes because TcLclEnv mentions WantedConstraints WantedConstraint mentions CtLoc CtLoc mentions ErrCtxt ErrCtxt mentions TcM * * v%************************************************************************ -} data WantedConstraints = WC { wc_simple :: Cts -- Unsolved constraints, all wanted , wc_impl :: Bag Implication , wc_insol :: Cts -- Insoluble constraints, can be -- wanted, given, or derived -- See Note [Insoluble constraints] } emptyWC :: WantedConstraints emptyWC = WC { wc_simple = emptyBag, wc_impl = emptyBag, wc_insol = emptyBag } mkSimpleWC :: [CtEvidence] -> WantedConstraints mkSimpleWC cts = WC { wc_simple = listToBag (map mkNonCanonical cts) , wc_impl = emptyBag , wc_insol = emptyBag } mkImplicWC :: Bag Implication -> WantedConstraints mkImplicWC implic = WC { wc_simple = emptyBag, wc_impl = implic, wc_insol = emptyBag } isEmptyWC :: WantedConstraints -> Bool isEmptyWC (WC { wc_simple = f, wc_impl = i, wc_insol = n }) = isEmptyBag f && isEmptyBag i && isEmptyBag n andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints andWC (WC { wc_simple = f1, wc_impl = i1, wc_insol = n1 }) (WC { wc_simple = f2, wc_impl = i2, wc_insol = n2 }) = WC { wc_simple = f1 `unionBags` f2 , wc_impl = i1 `unionBags` i2 , wc_insol = n1 `unionBags` n2 } unionsWC :: [WantedConstraints] -> WantedConstraints unionsWC = foldr andWC emptyWC -- | Convert all Wanteds into Deriveds (ignoring insolubles) toDerivedWC :: WantedConstraints -> WantedConstraints toDerivedWC wc@(WC { wc_simple = simples, wc_impl = implics }) = wc { wc_simple = mapBag toDerivedCt simples , wc_impl = mapBag to_derived_implic implics } where to_derived_implic implic@(Implic { ic_wanted = inner_wanted }) = implic { ic_wanted = toDerivedWC inner_wanted } addSimples :: WantedConstraints -> Bag Ct -> WantedConstraints addSimples wc cts = wc { wc_simple = wc_simple wc `unionBags` cts } -- Consider: Put the new constraints at the front, so they get solved first addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints addImplics wc implic = wc { wc_impl = wc_impl wc `unionBags` implic } addInsols :: WantedConstraints -> Bag Ct -> WantedConstraints addInsols wc cts = wc { wc_insol = wc_insol wc `unionBags` cts } getInsolubles :: WantedConstraints -> Cts getInsolubles = wc_insol dropDerivedWC :: WantedConstraints -> WantedConstraints -- See Note [Dropping derived constraints] dropDerivedWC wc@(WC { wc_simple = simples, wc_insol = insols }) = wc { wc_simple = dropDerivedSimples simples , wc_insol = dropDerivedInsols insols } -- The wc_impl implications are already (recursively) filtered isInsolubleStatus :: ImplicStatus -> Bool isInsolubleStatus IC_Insoluble = True isInsolubleStatus _ = False insolubleImplic :: Implication -> Bool insolubleImplic ic = isInsolubleStatus (ic_status ic) insolubleWC :: TcLevel -> WantedConstraints -> Bool insolubleWC tc_lvl (WC { wc_impl = implics, wc_insol = insols }) = anyBag (trulyInsoluble tc_lvl) insols || anyBag insolubleImplic implics trulyInsoluble :: TcLevel -> Ct -> Bool -- Constraints in the wc_insol set which ARE NOT -- treated as truly insoluble: -- a) type holes, arising from PartialTypeSignatures, -- b) "true" expression holes arising from TypedHoles -- -- Out-of-scope variables masquerading as expression holes -- ARE treated as truly insoluble. -- Yuk! trulyInsoluble _tc_lvl insol | isHoleCt insol = isOutOfScopeCt insol | otherwise = True instance Outputable WantedConstraints where ppr (WC {wc_simple = s, wc_impl = i, wc_insol = n}) = text "WC" <+> braces (vcat [ ppr_bag (text "wc_simple") s , ppr_bag (text "wc_insol") n , ppr_bag (text "wc_impl") i ]) ppr_bag :: Outputable a => SDoc -> Bag a -> SDoc ppr_bag doc bag | isEmptyBag bag = empty | otherwise = hang (doc <+> equals) 2 (foldrBag (($$) . ppr) empty bag) {- ************************************************************************ * * Implication constraints * * ************************************************************************ -} data Implication = Implic { ic_tclvl :: TcLevel, -- TcLevel: unification variables -- free in the environment ic_skols :: [TcTyVar], -- Introduced skolems ic_info :: SkolemInfo, -- See Note [Skolems in an implication] -- See Note [Shadowing in a constraint] ic_given :: [EvVar], -- Given evidence variables -- (order does not matter) -- See Invariant (GivenInv) in TcType ic_no_eqs :: Bool, -- True <=> ic_givens have no equalities, for sure -- False <=> ic_givens might have equalities ic_env :: TcLclEnv, -- Gives the source location and error context -- for the implication, and hence for all the -- given evidence variables ic_wanted :: WantedConstraints, -- The wanted ic_binds :: Maybe EvBindsVar, -- Points to the place to fill in the -- abstraction and bindings. -- is Nothing if we can't deal with -- non-equality constraints here -- (this happens in TcS.deferTcSForAllEq) ic_status :: ImplicStatus } data ImplicStatus = IC_Solved -- All wanteds in the tree are solved, all the way down { ics_need :: VarSet -- Evidence variables needed by this implication , ics_dead :: [EvVar] } -- Subset of ic_given that are not needed -- See Note [Tracking redundant constraints] in TcSimplify | IC_Insoluble -- At least one insoluble constraint in the tree | IC_Unsolved -- Neither of the above; might go either way instance Outputable Implication where ppr (Implic { ic_tclvl = tclvl, ic_skols = skols , ic_given = given, ic_no_eqs = no_eqs , ic_wanted = wanted, ic_status = status , ic_binds = binds, ic_info = info }) = hang (text "Implic" <+> lbrace) 2 (sep [ text "TcLevel =" <+> ppr tclvl , text "Skolems =" <+> pprTvBndrs skols , text "No-eqs =" <+> ppr no_eqs , text "Status =" <+> ppr status , hang (text "Given =") 2 (pprEvVars given) , hang (text "Wanted =") 2 (ppr wanted) , text "Binds =" <+> ppr binds , pprSkolInfo info ] <+> rbrace) instance Outputable ImplicStatus where ppr IC_Insoluble = text "Insoluble" ppr IC_Unsolved = text "Unsolved" ppr (IC_Solved { ics_need = vs, ics_dead = dead }) = text "Solved" <+> (braces $ vcat [ text "Dead givens =" <+> ppr dead , text "Needed =" <+> ppr vs ]) {- Note [Needed evidence variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Th ic_need_evs field holds the free vars of ic_binds, and all the ic_binds in nested implications. * Main purpose: if one of the ic_givens is not mentioned in here, it is redundant. * solveImplication may drop an implication altogether if it has no remaining 'wanteds'. But we still track the free vars of its evidence binds, even though it has now disappeared. Note [Shadowing in a constraint] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We assume NO SHADOWING in a constraint. Specifically * The unification variables are all implicitly quantified at top level, and are all unique * The skolem variables bound in ic_skols are all freah when the implication is created. So we can safely substitute. For example, if we have forall a. a~Int => ...(forall b. ...a...)... we can push the (a~Int) constraint inwards in the "givens" without worrying that 'b' might clash. Note [Skolems in an implication] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The skolems in an implication are not there to perform a skolem escape check. That happens because all the environment variables are in the untouchables, and therefore cannot be unified with anything at all, let alone the skolems. Instead, ic_skols is used only when considering floating a constraint outside the implication in TcSimplify.floatEqualities or TcSimplify.approximateImplications Note [Insoluble constraints] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Some of the errors that we get during canonicalization are best reported when all constraints have been simplified as much as possible. For instance, assume that during simplification the following constraints arise: [Wanted] F alpha ~ uf1 [Wanted] beta ~ uf1 beta When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail we will simply see a message: 'Can't construct the infinite type beta ~ uf1 beta' and the user has no idea what the uf1 variable is. Instead our plan is that we will NOT fail immediately, but: (1) Record the "frozen" error in the ic_insols field (2) Isolate the offending constraint from the rest of the inerts (3) Keep on simplifying/canonicalizing At the end, we will hopefully have substituted uf1 := F alpha, and we will be able to report a more informative error: 'Can't construct the infinite type beta ~ F alpha beta' Insoluble constraints *do* include Derived constraints. For example, a functional dependency might give rise to [D] Int ~ Bool, and we must report that. If insolubles did not contain Deriveds, reportErrors would never see it. ************************************************************************ * * Pretty printing * * ************************************************************************ -} pprEvVars :: [EvVar] -> SDoc -- Print with their types pprEvVars ev_vars = vcat (map pprEvVarWithType ev_vars) pprEvVarTheta :: [EvVar] -> SDoc pprEvVarTheta ev_vars = pprTheta (map evVarPred ev_vars) pprEvVarWithType :: EvVar -> SDoc pprEvVarWithType v = ppr v <+> dcolon <+> pprType (evVarPred v) {- ************************************************************************ * * CtEvidence * * ************************************************************************ Note [Evidence field of CtEvidence] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ During constraint solving we never look at the type of ctev_evar/ctev_dest; instead we look at the ctev_pred field. The evtm/evar field may be un-zonked. Note [Bind new Givens immediately] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For Givens we make new EvVars and bind them immediately. Two main reasons: * Gain sharing. E.g. suppose we start with g :: C a b, where class D a => C a b class (E a, F a) => D a If we generate all g's superclasses as separate EvTerms we might get selD1 (selC1 g) :: E a selD2 (selC1 g) :: F a selC1 g :: D a which we could do more economically as: g1 :: D a = selC1 g g2 :: E a = selD1 g1 g3 :: F a = selD2 g1 * For *coercion* evidence we *must* bind each given: class (a~b) => C a b where .... f :: C a b => .... Then in f's Givens we have g:(C a b) and the superclass sc(g,0):a~b. But that superclass selector can't (yet) appear in a coercion (see evTermCoercion), so the easy thing is to bind it to an Id. So a Given has EvVar inside it rather than (as previously) an EvTerm. -} -- | A place for type-checking evidence to go after it is generated. -- Wanted equalities are always HoleDest; other wanteds are always -- EvVarDest. data TcEvDest = EvVarDest EvVar -- ^ bind this var to the evidence | HoleDest CoercionHole -- ^ fill in this hole with the evidence -- See Note [Coercion holes] in TyCoRep data CtEvidence = CtGiven { ctev_pred :: TcPredType -- See Note [Ct/evidence invariant] , ctev_evar :: EvVar -- See Note [Evidence field of CtEvidence] , ctev_loc :: CtLoc } -- Truly given, not depending on subgoals -- NB: Spontaneous unifications belong here | CtWanted { ctev_pred :: TcPredType -- See Note [Ct/evidence invariant] , ctev_dest :: TcEvDest , ctev_loc :: CtLoc } -- Wanted goal | CtDerived { ctev_pred :: TcPredType , ctev_loc :: CtLoc } -- A goal that we don't really have to solve and can't immediately -- rewrite anything other than a derived (there's no evidence!) -- but if we do manage to solve it may help in solving other goals. ctEvPred :: CtEvidence -> TcPredType -- The predicate of a flavor ctEvPred = ctev_pred ctEvLoc :: CtEvidence -> CtLoc ctEvLoc = ctev_loc ctEvOrigin :: CtEvidence -> CtOrigin ctEvOrigin = ctLocOrigin . ctEvLoc -- | Get the equality relation relevant for a 'CtEvidence' ctEvEqRel :: CtEvidence -> EqRel ctEvEqRel = predTypeEqRel . ctEvPred -- | Get the role relevant for a 'CtEvidence' ctEvRole :: CtEvidence -> Role ctEvRole = eqRelRole . ctEvEqRel ctEvTerm :: CtEvidence -> EvTerm ctEvTerm ev@(CtWanted { ctev_dest = HoleDest _ }) = EvCoercion $ ctEvCoercion ev ctEvTerm ev = EvId (ctEvId ev) ctEvCoercion :: CtEvidence -> Coercion ctEvCoercion ev@(CtWanted { ctev_dest = HoleDest hole, ctev_pred = pred }) = case getEqPredTys_maybe pred of Just (role, ty1, ty2) -> mkHoleCo hole role ty1 ty2 _ -> pprPanic "ctEvTerm" (ppr ev) ctEvCoercion (CtGiven { ctev_evar = ev_id }) = mkTcCoVarCo ev_id ctEvCoercion ev = pprPanic "ctEvCoercion" (ppr ev) ctEvId :: CtEvidence -> TcId ctEvId (CtWanted { ctev_dest = EvVarDest ev }) = ev ctEvId (CtGiven { ctev_evar = ev }) = ev ctEvId ctev = pprPanic "ctEvId:" (ppr ctev) instance Outputable TcEvDest where ppr (HoleDest h) = text "hole" <> ppr h ppr (EvVarDest ev) = ppr ev instance Outputable CtEvidence where ppr fl = case fl of CtGiven {} -> text "[G]" <+> ppr (ctev_evar fl) <+> ppr_pty CtWanted {} -> text "[W]" <+> ppr (ctev_dest fl) <+> ppr_pty CtDerived {} -> text "[D]" <+> text "_" <+> ppr_pty where ppr_pty = dcolon <+> ppr (ctEvPred fl) isWanted :: CtEvidence -> Bool isWanted (CtWanted {}) = True isWanted _ = False isGiven :: CtEvidence -> Bool isGiven (CtGiven {}) = True isGiven _ = False isDerived :: CtEvidence -> Bool isDerived (CtDerived {}) = True isDerived _ = False {- %************************************************************************ %* * CtFlavour %* * %************************************************************************ Just an enum type that tracks whether a constraint is wanted, derived, or given, when we need to separate that info from the constraint itself. -} data CtFlavour = Given | Wanted | Derived deriving Eq instance Outputable CtFlavour where ppr Given = text "[G]" ppr Wanted = text "[W]" ppr Derived = text "[D]" ctEvFlavour :: CtEvidence -> CtFlavour ctEvFlavour (CtWanted {}) = Wanted ctEvFlavour (CtGiven {}) = Given ctEvFlavour (CtDerived {}) = Derived -- | Whether or not one 'Ct' can rewrite another is determined by its -- flavour and its equality relation. See also -- Note [Flavours with roles] in TcSMonad type CtFlavourRole = (CtFlavour, EqRel) -- | Extract the flavour, role, and boxity from a 'CtEvidence' ctEvFlavourRole :: CtEvidence -> CtFlavourRole ctEvFlavourRole ev = (ctEvFlavour ev, ctEvEqRel ev) -- | Extract the flavour, role, and boxity from a 'Ct' ctFlavourRole :: Ct -> CtFlavourRole ctFlavourRole = ctEvFlavourRole . cc_ev {- Note [eqCanRewrite] ~~~~~~~~~~~~~~~~~~~ (eqCanRewrite ct1 ct2) holds if the constraint ct1 (a CTyEqCan of form tv ~ ty) can be used to rewrite ct2. It must satisfy the properties of a can-rewrite relation, see Definition [Can-rewrite relation] in TcSMonad. With the solver handling Coercible constraints like equality constraints, the rewrite conditions must take role into account, never allowing a representational equality to rewrite a nominal one. Note [Wanteds do not rewrite Wanteds] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We don't allow Wanteds to rewrite Wanteds, because that can give rise to very confusing type error messages. A good example is Trac #8450. Here's another f :: a -> Bool f x = ( [x,'c'], [x,True] ) `seq` True Here we get [W] a ~ Char [W] a ~ Bool but we do not want to complain about Bool ~ Char! Note [Deriveds do rewrite Deriveds] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ However we DO allow Deriveds to rewrite Deriveds, because that's how improvement works; see Note [The improvement story] in TcInteract. However, for now at least I'm only letting (Derived,NomEq) rewrite (Derived,NomEq) and not doing anything for ReprEq. If we have eqCanRewriteFR (Derived, NomEq) (Derived, _) = True then we lose property R2 of Definition [Can-rewrite relation] in TcSMonad R2. If f1 >= f, and f2 >= f, then either f1 >= f2 or f2 >= f1 Consider f1 = (Given, ReprEq) f2 = (Derived, NomEq) f = (Derived, ReprEq) I thought maybe we could never get Derived ReprEq constraints, but we can; straight from the Wanteds during improvment. And from a Derived ReprEq we could conceivably get a Derived NomEq improvment (by decomposing a type constructor with Nomninal role), and hence unify. Note [funEqCanDischarge] ~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose we have two CFunEqCans with the same LHS: (x1:F ts ~ f1) `funEqCanDischarge` (x2:F ts ~ f2) Can we drop x2 in favour of x1, either unifying f2 (if it's a flatten meta-var) or adding a new Given (f1 ~ f2), if x2 is a Given? Answer: yes if funEqCanDischarge is true. Note [eqCanDischarge] ~~~~~~~~~~~~~~~~~~~~~ Suppose we have two identicla equality constraints (i.e. both LHS and RHS are the same) (x1:s~t) `eqCanDischarge` (xs:s~t) Can we just drop x2 in favour of x1? Answer: yes if eqCanDischarge is true. Note that we do /not/ allow Wanted to discharge Derived. We must keep both. Why? Because the Derived may rewrite other Deriveds in the model whereas the Wanted cannot. However a Wanted can certainly discharge an identical Wanted. So eqCanDischarge does /not/ define a can-rewrite relation in the sense of Definition [Can-rewrite relation] in TcSMonad. -} ----------------- eqCanRewrite :: CtEvidence -> CtEvidence -> Bool -- Very important function! -- See Note [eqCanRewrite] -- See Note [Wanteds do not rewrite Wanteds] -- See Note [Deriveds do rewrite Deriveds] eqCanRewrite ev1 ev2 = eqCanRewriteFR (ctEvFlavourRole ev1) (ctEvFlavourRole ev2) eqCanRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool eqCanRewriteFR (Given, NomEq) (_, _) = True eqCanRewriteFR (Given, ReprEq) (_, ReprEq) = True eqCanRewriteFR (Derived, NomEq) (Derived, NomEq) = True eqCanRewriteFR _ _ = False ----------------- funEqCanDischarge :: CtEvidence -> CtEvidence -> Bool -- See Note [funEqCanDischarge] funEqCanDischarge ev1 ev2 = funEqCanDischargeFR (ctEvFlavourRole ev1) (ctEvFlavourRole ev2) funEqCanDischargeFR :: CtFlavourRole -> CtFlavourRole -> Bool funEqCanDischargeFR (_, ReprEq) (_, NomEq) = False funEqCanDischargeFR (Given, _) _ = True funEqCanDischargeFR (Wanted, _) (Wanted, _) = True funEqCanDischargeFR (Wanted, _) (Derived, _) = True funEqCanDischargeFR (Derived, _) (Derived, _) = True funEqCanDischargeFR _ _ = False ----------------- eqCanDischarge :: CtEvidence -> CtEvidence -> Bool -- See Note [eqCanDischarge] eqCanDischarge ev1 ev2 = eqCanDischargeFR (ctEvFlavourRole ev1) (ctEvFlavourRole ev2) eqCanDischargeFR :: CtFlavourRole -> CtFlavourRole -> Bool eqCanDischargeFR (_, ReprEq) (_, NomEq) = False eqCanDischargeFR (Given, _) (Given,_) = True eqCanDischargeFR (Wanted, _) (Wanted, _) = True eqCanDischargeFR (Derived, _) (Derived, _) = True eqCanDischargeFR _ _ = False {- ************************************************************************ * * SubGoalDepth * * ************************************************************************ Note [SubGoalDepth] ~~~~~~~~~~~~~~~~~~~ The 'SubGoalDepth' takes care of stopping the constraint solver from looping. The counter starts at zero and increases. It includes dictionary constraints, equality simplification, and type family reduction. (Why combine these? Because it's actually quite easy to mistake one for another, in sufficiently involved scenarios, like ConstraintKinds.) The flag -fcontext-stack=n (not very well named!) fixes the maximium level. * The counter includes the depth of type class instance declarations. Example: [W] d{7} : Eq [Int] That is d's dictionary-constraint depth is 7. If we use the instance $dfEqList :: Eq a => Eq [a] to simplify it, we get d{7} = $dfEqList d'{8} where d'{8} : Eq Int, and d' has depth 8. For civilised (decidable) instance declarations, each increase of depth removes a type constructor from the type, so the depth never gets big; i.e. is bounded by the structural depth of the type. * The counter also increments when resolving equalities involving type functions. Example: Assume we have a wanted at depth 7: [W] d{7} : F () ~ a If there is an type function equation "F () = Int", this would be rewritten to [W] d{8} : Int ~ a and remembered as having depth 8. Again, without UndecidableInstances, this counter is bounded, but without it can resolve things ad infinitum. Hence there is a maximum level. * Lastly, every time an equality is rewritten, the counter increases. Again, rewriting an equality constraint normally makes progress, but it's possible the "progress" is just the reduction of an infinitely-reducing type family. Hence we need to track the rewrites. When compiling a program requires a greater depth, then GHC recommends turning off this check entirely by setting -freduction-depth=0. This is because the exact number that works is highly variable, and is likely to change even between minor releases. Because this check is solely to prevent infinite compilation times, it seems safe to disable it when a user has ascertained that their program doesn't loop at the type level. -} -- | See Note [SubGoalDepth] newtype SubGoalDepth = SubGoalDepth Int deriving (Eq, Ord, Outputable) initialSubGoalDepth :: SubGoalDepth initialSubGoalDepth = SubGoalDepth 0 bumpSubGoalDepth :: SubGoalDepth -> SubGoalDepth bumpSubGoalDepth (SubGoalDepth n) = SubGoalDepth (n + 1) subGoalDepthExceeded :: DynFlags -> SubGoalDepth -> Bool subGoalDepthExceeded dflags (SubGoalDepth d) = mkIntWithInf d > reductionDepth dflags {- ************************************************************************ * * CtLoc * * ************************************************************************ The 'CtLoc' gives information about where a constraint came from. This is important for decent error message reporting because dictionaries don't appear in the original source code. type will evolve... -} data CtLoc = CtLoc { ctl_origin :: CtOrigin , ctl_env :: TcLclEnv , ctl_t_or_k :: Maybe TypeOrKind -- OK if we're not sure , ctl_depth :: !SubGoalDepth } -- The TcLclEnv includes particularly -- source location: tcl_loc :: RealSrcSpan -- context: tcl_ctxt :: [ErrCtxt] -- binder stack: tcl_bndrs :: TcIdBinderStack -- level: tcl_tclvl :: TcLevel mkGivenLoc :: TcLevel -> SkolemInfo -> TcLclEnv -> CtLoc mkGivenLoc tclvl skol_info env = CtLoc { ctl_origin = GivenOrigin skol_info , ctl_env = env { tcl_tclvl = tclvl } , ctl_t_or_k = Nothing -- this only matters for error msgs , ctl_depth = initialSubGoalDepth } mkKindLoc :: TcType -> TcType -- original *types* being compared -> CtLoc -> CtLoc mkKindLoc s1 s2 loc = setCtLocOrigin (toKindLoc loc) (KindEqOrigin s1 (Just s2) (ctLocOrigin loc) (ctLocTypeOrKind_maybe loc)) -- | Take a CtLoc and moves it to the kind level toKindLoc :: CtLoc -> CtLoc toKindLoc loc = loc { ctl_t_or_k = Just KindLevel } ctLocEnv :: CtLoc -> TcLclEnv ctLocEnv = ctl_env ctLocLevel :: CtLoc -> TcLevel ctLocLevel loc = tcl_tclvl (ctLocEnv loc) ctLocDepth :: CtLoc -> SubGoalDepth ctLocDepth = ctl_depth ctLocOrigin :: CtLoc -> CtOrigin ctLocOrigin = ctl_origin ctLocSpan :: CtLoc -> RealSrcSpan ctLocSpan (CtLoc { ctl_env = lcl}) = tcl_loc lcl ctLocTypeOrKind_maybe :: CtLoc -> Maybe TypeOrKind ctLocTypeOrKind_maybe = ctl_t_or_k setCtLocSpan :: CtLoc -> RealSrcSpan -> CtLoc setCtLocSpan ctl@(CtLoc { ctl_env = lcl }) loc = setCtLocEnv ctl (lcl { tcl_loc = loc }) bumpCtLocDepth :: CtLoc -> CtLoc bumpCtLocDepth loc@(CtLoc { ctl_depth = d }) = loc { ctl_depth = bumpSubGoalDepth d } setCtLocOrigin :: CtLoc -> CtOrigin -> CtLoc setCtLocOrigin ctl orig = ctl { ctl_origin = orig } setCtLocEnv :: CtLoc -> TcLclEnv -> CtLoc setCtLocEnv ctl env = ctl { ctl_env = env } pushErrCtxt :: CtOrigin -> ErrCtxt -> CtLoc -> CtLoc pushErrCtxt o err loc@(CtLoc { ctl_env = lcl }) = loc { ctl_origin = o, ctl_env = lcl { tcl_ctxt = err : tcl_ctxt lcl } } pushErrCtxtSameOrigin :: ErrCtxt -> CtLoc -> CtLoc -- Just add information w/o updating the origin! pushErrCtxtSameOrigin err loc@(CtLoc { ctl_env = lcl }) = loc { ctl_env = lcl { tcl_ctxt = err : tcl_ctxt lcl } } {- ************************************************************************ * * SkolemInfo * * ************************************************************************ -} -- SkolemInfo gives the origin of *given* constraints -- a) type variables are skolemised -- b) an implication constraint is generated data SkolemInfo = SigSkol UserTypeCtxt -- A skolem that is created by instantiating ExpType -- a programmer-supplied type signature -- Location of the binding site is on the TyVar | PatSynSigSkol Name -- Bound by a programmer-supplied type signature of a pattern -- synonym. Here we cannot use a SigSkol, see -- Note [Patterns synonyms and the data type Type] in -- basicTypes\PatSyn.hs | ClsSkol Class -- Bound at a class decl | DerivSkol Type -- Bound by a 'deriving' clause; -- the type is the instance we are trying to derive | InstSkol -- Bound at an instance decl | InstSC TypeSize -- A "given" constraint obtained by superclass selection. -- If (C ty1 .. tyn) is the largest class from -- which we made a superclass selection in the chain, -- then TypeSize = sizeTypes [ty1, .., tyn] -- See Note [Solving superclass constraints] in TcInstDcls | DataSkol -- Bound at a data type declaration | FamInstSkol -- Bound at a family instance decl | PatSkol -- An existential type variable bound by a pattern for ConLike -- a data constructor with an existential type. (HsMatchContext Name) -- e.g. data T = forall a. Eq a => MkT a -- f (MkT x) = ... -- The pattern MkT x will allocate an existential type -- variable for 'a'. | ArrowSkol -- An arrow form (see TcArrows) | IPSkol [HsIPName] -- Binding site of an implicit parameter | RuleSkol RuleName -- The LHS of a RULE | InferSkol [(Name,TcType)] -- We have inferred a type for these (mutually-recursivive) -- polymorphic Ids, and are now checking that their RHS -- constraints are satisfied. | BracketSkol -- Template Haskell bracket | UnifyForAllSkol -- We are unifying two for-all types TcType -- The instantiated type *inside* the forall | UnkSkol -- Unhelpful info (until I improve it) instance Outputable SkolemInfo where ppr = pprSkolInfo pprSkolInfo :: SkolemInfo -> SDoc -- Complete the sentence "is a rigid type variable bound by..." pprSkolInfo (SigSkol ctxt ty) = pprSigSkolInfo ctxt ty pprSkolInfo (IPSkol ips) = text "the implicit-parameter binding" <> plural ips <+> text "for" <+> pprWithCommas ppr ips pprSkolInfo (ClsSkol cls) = text "the class declaration for" <+> quotes (ppr cls) pprSkolInfo (DerivSkol pred) = text "the deriving clause for" <+> quotes (ppr pred) pprSkolInfo InstSkol = text "the instance declaration" pprSkolInfo (InstSC n) = text "the instance declaration" <> ifPprDebug (parens (ppr n)) pprSkolInfo DataSkol = text "a data type declaration" pprSkolInfo FamInstSkol = text "a family instance declaration" pprSkolInfo BracketSkol = text "a Template Haskell bracket" pprSkolInfo (RuleSkol name) = text "the RULE" <+> pprRuleName name pprSkolInfo ArrowSkol = text "an arrow form" pprSkolInfo (PatSkol cl mc) = sep [ pprPatSkolInfo cl , text "in" <+> pprMatchContext mc ] pprSkolInfo (InferSkol ids) = sep [ text "the inferred type of" , vcat [ ppr name <+> dcolon <+> ppr ty | (name,ty) <- ids ]] pprSkolInfo (UnifyForAllSkol ty) = text "the type" <+> ppr ty pprSkolInfo (PatSynSigSkol name) = text "the type signature of pattern synonym" <+> quotes (ppr name) -- UnkSkol -- For type variables the others are dealt with by pprSkolTvBinding. -- For Insts, these cases should not happen pprSkolInfo UnkSkol = WARN( True, text "pprSkolInfo: UnkSkol" ) text "UnkSkol" pprSigSkolInfo :: UserTypeCtxt -> ExpType -> SDoc pprSigSkolInfo ctxt ty = case ctxt of FunSigCtxt f _ -> pp_sig f _ -> vcat [ pprUserTypeCtxt ctxt <> colon , nest 2 (ppr ty) ] where pp_sig f = vcat [ text "the type signature for:" , nest 2 (pprPrefixOcc f <+> dcolon <+> ppr ty) ] pprPatSkolInfo :: ConLike -> SDoc pprPatSkolInfo (RealDataCon dc) = sep [ text "a pattern with constructor:" , nest 2 $ ppr dc <+> dcolon <+> pprType (dataConUserType dc) <> comma ] -- pprType prints forall's regardless of -fprint-explict-foralls -- which is what we want here, since we might be saying -- type variable 't' is bound by ... pprPatSkolInfo (PatSynCon ps) = sep [ text "a pattern with pattern synonym:" , nest 2 $ ppr ps <+> dcolon <+> pprPatSynType ps <> comma ] {- ************************************************************************ * * CtOrigin * * ************************************************************************ -} data CtOrigin = GivenOrigin SkolemInfo -- All the others are for *wanted* constraints | OccurrenceOf Name -- Occurrence of an overloaded identifier | OccurrenceOfRecSel RdrName -- Occurrence of a record selector | AppOrigin -- An application of some kind | SpecPragOrigin UserTypeCtxt -- Specialisation pragma for -- function or instance | TypeEqOrigin { uo_actual :: TcType , uo_expected :: ExpType , uo_thing :: Maybe ErrorThing -- ^ The thing that has type "actual" } | KindEqOrigin TcType (Maybe TcType) -- A kind equality arising from unifying these two types CtOrigin -- originally arising from this (Maybe TypeOrKind) -- the level of the eq this arises from | IPOccOrigin HsIPName -- Occurrence of an implicit parameter | OverLabelOrigin FastString -- Occurrence of an overloaded label | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal | NegateOrigin -- Occurrence of syntactic negation | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:] | SectionOrigin | TupleOrigin -- (..,..) | ExprSigOrigin -- e :: ty | PatSigOrigin -- p :: ty | PatOrigin -- Instantiating a polytyped pattern at a constructor | ProvCtxtOrigin -- The "provided" context of a pattern synonym signature (PatSynBind Name Name) -- Information about the pattern synonym, in particular -- the name and the right-hand side | RecordUpdOrigin | ViewPatOrigin | ScOrigin TypeSize -- Typechecking superclasses of an instance declaration -- If the instance head is C ty1 .. tyn -- then TypeSize = sizeTypes [ty1, .., tyn] -- See Note [Solving superclass constraints] in TcInstDcls | DerivOrigin -- Typechecking deriving | DerivOriginDC DataCon Int -- Checking constraints arising from this data con and field index | DerivOriginCoerce Id Type Type -- DerivOriginCoerce id ty1 ty2: Trying to coerce class method `id` from -- `ty1` to `ty2`. | StandAloneDerivOrigin -- Typechecking stand-alone deriving | DefaultOrigin -- Typechecking a default decl | DoOrigin -- Arising from a do expression | DoPatOrigin (LPat Name) -- Arising from a failable pattern in -- a do expression | MCompOrigin -- Arising from a monad comprehension | MCompPatOrigin (LPat Name) -- Arising from a failable pattern in a -- monad comprehension | IfOrigin -- Arising from an if statement | ProcOrigin -- Arising from a proc expression | AnnOrigin -- An annotation | FunDepOrigin1 -- A functional dependency from combining PredType CtLoc -- This constraint arising from ... PredType CtLoc -- and this constraint arising from ... | FunDepOrigin2 -- A functional dependency from combining PredType CtOrigin -- This constraint arising from ... PredType SrcSpan -- and this instance -- We only need a CtOrigin on the first, because the location -- is pinned on the entire error message | HoleOrigin | UnboundOccurrenceOf OccName | ListOrigin -- An overloaded list | StaticOrigin -- A static form | FailablePattern (LPat TcId) -- A failable pattern in do-notation for the -- MonadFail Proposal (MFP). Obsolete when -- actual desugaring to MonadFail.fail is live. | Shouldn'tHappenOrigin String -- the user should never see this one, -- unlesss ImpredicativeTypes is on, where all -- bets are off -- | A thing that can be stored for error message generation only. -- It is stored with a function to zonk and tidy the thing. data ErrorThing = forall a. Outputable a => ErrorThing a (Maybe Arity) -- # of args, if known (TidyEnv -> a -> TcM (TidyEnv, a)) -- | Flag to see whether we're type-checking terms or kind-checking types data TypeOrKind = TypeLevel | KindLevel deriving Eq instance Outputable TypeOrKind where ppr TypeLevel = text "TypeLevel" ppr KindLevel = text "KindLevel" isTypeLevel :: TypeOrKind -> Bool isTypeLevel TypeLevel = True isTypeLevel KindLevel = False isKindLevel :: TypeOrKind -> Bool isKindLevel TypeLevel = False isKindLevel KindLevel = True -- | Make an 'ErrorThing' that doesn't need tidying or zonking mkErrorThing :: Outputable a => a -> ErrorThing mkErrorThing thing = ErrorThing thing Nothing (\env x -> return (env, x)) -- | Retrieve the # of arguments in the error thing, if known errorThingNumArgs_maybe :: ErrorThing -> Maybe Arity errorThingNumArgs_maybe (ErrorThing _ args _) = args instance Outputable CtOrigin where ppr = pprCtOrigin instance Outputable ErrorThing where ppr (ErrorThing thing _ _) = ppr thing ctoHerald :: SDoc ctoHerald = ptext (sLit "arising from") -- | Extract a suitable CtOrigin from a HsExpr exprCtOrigin :: HsExpr Name -> CtOrigin exprCtOrigin (HsVar (L _ name)) = OccurrenceOf name exprCtOrigin (HsUnboundVar uv) = UnboundOccurrenceOf (unboundVarOcc uv) exprCtOrigin (HsRecFld f) = OccurrenceOfRecSel (rdrNameAmbiguousFieldOcc f) exprCtOrigin (HsOverLabel l) = OverLabelOrigin l exprCtOrigin (HsIPVar ip) = IPOccOrigin ip exprCtOrigin (HsOverLit lit) = LiteralOrigin lit exprCtOrigin (HsLit {}) = Shouldn'tHappenOrigin "concrete literal" exprCtOrigin (HsLam matches) = matchesCtOrigin matches exprCtOrigin (HsLamCase _ ms) = matchesCtOrigin ms exprCtOrigin (HsApp (L _ e1) _) = exprCtOrigin e1 exprCtOrigin (HsAppType (L _ e1) _) = exprCtOrigin e1 exprCtOrigin (HsAppTypeOut {}) = panic "exprCtOrigin HsAppTypeOut" exprCtOrigin (OpApp _ (L _ op) _ _) = exprCtOrigin op exprCtOrigin (NegApp (L _ e) _) = exprCtOrigin e exprCtOrigin (HsPar (L _ e)) = exprCtOrigin e exprCtOrigin (SectionL _ _) = SectionOrigin exprCtOrigin (SectionR _ _) = SectionOrigin exprCtOrigin (ExplicitTuple {}) = Shouldn'tHappenOrigin "explicit tuple" exprCtOrigin (HsCase _ matches) = matchesCtOrigin matches exprCtOrigin (HsIf (Just syn) _ _ _) = exprCtOrigin (syn_expr syn) exprCtOrigin (HsIf {}) = Shouldn'tHappenOrigin "if expression" exprCtOrigin (HsMultiIf _ rhs) = lGRHSCtOrigin rhs exprCtOrigin (HsLet _ (L _ e)) = exprCtOrigin e exprCtOrigin (HsDo _ _ _) = DoOrigin exprCtOrigin (ExplicitList {}) = Shouldn'tHappenOrigin "list" exprCtOrigin (ExplicitPArr {}) = Shouldn'tHappenOrigin "parallel array" exprCtOrigin (RecordCon {}) = Shouldn'tHappenOrigin "record construction" exprCtOrigin (RecordUpd {}) = Shouldn'tHappenOrigin "record update" exprCtOrigin (ExprWithTySig {}) = ExprSigOrigin exprCtOrigin (ExprWithTySigOut {}) = panic "exprCtOrigin ExprWithTySigOut" exprCtOrigin (ArithSeq {}) = Shouldn'tHappenOrigin "arithmetic sequence" exprCtOrigin (PArrSeq {}) = Shouldn'tHappenOrigin "parallel array sequence" exprCtOrigin (HsSCC _ _ (L _ e))= exprCtOrigin e exprCtOrigin (HsCoreAnn _ _ (L _ e)) = exprCtOrigin e exprCtOrigin (HsBracket {}) = Shouldn'tHappenOrigin "TH bracket" exprCtOrigin (HsRnBracketOut {})= Shouldn'tHappenOrigin "HsRnBracketOut" exprCtOrigin (HsTcBracketOut {})= panic "exprCtOrigin HsTcBracketOut" exprCtOrigin (HsSpliceE {}) = Shouldn'tHappenOrigin "TH splice" exprCtOrigin (HsProc {}) = Shouldn'tHappenOrigin "proc" exprCtOrigin (HsStatic {}) = Shouldn'tHappenOrigin "static expression" exprCtOrigin (HsArrApp {}) = panic "exprCtOrigin HsArrApp" exprCtOrigin (HsArrForm {}) = panic "exprCtOrigin HsArrForm" exprCtOrigin (HsTick _ (L _ e)) = exprCtOrigin e exprCtOrigin (HsBinTick _ _ (L _ e)) = exprCtOrigin e exprCtOrigin (HsTickPragma _ _ _ (L _ e)) = exprCtOrigin e exprCtOrigin EWildPat = panic "exprCtOrigin EWildPat" exprCtOrigin (EAsPat {}) = panic "exprCtOrigin EAsPat" exprCtOrigin (EViewPat {}) = panic "exprCtOrigin EViewPat" exprCtOrigin (ELazyPat {}) = panic "exprCtOrigin ELazyPat" exprCtOrigin (HsWrap {}) = panic "exprCtOrigin HsWrap" -- | Extract a suitable CtOrigin from a MatchGroup matchesCtOrigin :: MatchGroup Name (LHsExpr Name) -> CtOrigin matchesCtOrigin (MG { mg_alts = alts }) | L _ [L _ match] <- alts , Match { m_grhss = grhss } <- match = grhssCtOrigin grhss | otherwise = Shouldn'tHappenOrigin "multi-way match" -- | Extract a suitable CtOrigin from guarded RHSs grhssCtOrigin :: GRHSs Name (LHsExpr Name) -> CtOrigin grhssCtOrigin (GRHSs { grhssGRHSs = lgrhss }) = lGRHSCtOrigin lgrhss -- | Extract a suitable CtOrigin from a list of guarded RHSs lGRHSCtOrigin :: [LGRHS Name (LHsExpr Name)] -> CtOrigin lGRHSCtOrigin [L _ (GRHS _ (L _ e))] = exprCtOrigin e lGRHSCtOrigin _ = Shouldn'tHappenOrigin "multi-way GRHS" pprCtLoc :: CtLoc -> SDoc -- "arising from ... at ..." -- Not an instance of Outputable because of the "arising from" prefix pprCtLoc (CtLoc { ctl_origin = o, ctl_env = lcl}) = sep [ pprCtOrigin o , text "at" <+> ppr (tcl_loc lcl)] pprCtOrigin :: CtOrigin -> SDoc -- "arising from ..." -- Not an instance of Outputable because of the "arising from" prefix pprCtOrigin (GivenOrigin sk) = ctoHerald <+> ppr sk pprCtOrigin (SpecPragOrigin ctxt) = case ctxt of FunSigCtxt n _ -> text "a SPECIALISE pragma for" <+> quotes (ppr n) SpecInstCtxt -> text "a SPECIALISE INSTANCE pragma" _ -> text "a SPECIALISE pragma" -- Never happens I think pprCtOrigin (FunDepOrigin1 pred1 loc1 pred2 loc2) = hang (ctoHerald <+> text "a functional dependency between constraints:") 2 (vcat [ hang (quotes (ppr pred1)) 2 (pprCtLoc loc1) , hang (quotes (ppr pred2)) 2 (pprCtLoc loc2) ]) pprCtOrigin (FunDepOrigin2 pred1 orig1 pred2 loc2) = hang (ctoHerald <+> text "a functional dependency between:") 2 (vcat [ hang (text "constraint" <+> quotes (ppr pred1)) 2 (pprCtOrigin orig1 ) , hang (text "instance" <+> quotes (ppr pred2)) 2 (text "at" <+> ppr loc2) ]) pprCtOrigin (KindEqOrigin t1 (Just t2) _ _) = hang (ctoHerald <+> text "a kind equality arising from") 2 (sep [ppr t1, char '~', ppr t2]) pprCtOrigin (KindEqOrigin t1 Nothing _ _) = hang (ctoHerald <+> text "a kind equality when matching") 2 (ppr t1) pprCtOrigin (UnboundOccurrenceOf name) = ctoHerald <+> text "an undeclared identifier" <+> quotes (ppr name) pprCtOrigin (DerivOriginDC dc n) = hang (ctoHerald <+> text "the" <+> speakNth n <+> text "field of" <+> quotes (ppr dc)) 2 (parens (text "type" <+> quotes (ppr ty))) where ty = dataConOrigArgTys dc !! (n-1) pprCtOrigin (DerivOriginCoerce meth ty1 ty2) = hang (ctoHerald <+> text "the coercion of the method" <+> quotes (ppr meth)) 2 (sep [ text "from type" <+> quotes (ppr ty1) , nest 2 $ text "to type" <+> quotes (ppr ty2) ]) pprCtOrigin (DoPatOrigin pat) = ctoHerald <+> text "a do statement" $$ text "with the failable pattern" <+> quotes (ppr pat) pprCtOrigin (MCompPatOrigin pat) = ctoHerald <+> hsep [ text "the failable pattern" , quotes (ppr pat) , text "in a statement in a monad comprehension" ] pprCtOrigin (FailablePattern pat) = ctoHerald <+> text "the failable pattern" <+> quotes (ppr pat) $$ text "(this will become an error in a future GHC release)" pprCtOrigin (Shouldn'tHappenOrigin note) = sdocWithDynFlags $ \dflags -> if xopt LangExt.ImpredicativeTypes dflags then text "a situation created by impredicative types" else vcat [ text "<< This should not appear in error messages. If you see this" , text "in an error message, please report a bug mentioning" <+> quotes (text note) <+> text "at" , text "https://ghc.haskell.org/trac/ghc/wiki/ReportABug >>" ] pprCtOrigin (ProvCtxtOrigin PSB{ psb_id = (L _ name) }) = hang (ctoHerald <+> text "the \"provided\" constraints claimed by") 2 (text "the signature of" <+> quotes (ppr name)) pprCtOrigin simple_origin = ctoHerald <+> pprCtO simple_origin -- | Short one-liners pprCtO :: CtOrigin -> SDoc pprCtO (OccurrenceOf name) = hsep [text "a use of", quotes (ppr name)] pprCtO (OccurrenceOfRecSel name) = hsep [text "a use of", quotes (ppr name)] pprCtO AppOrigin = text "an application" pprCtO (IPOccOrigin name) = hsep [text "a use of implicit parameter", quotes (ppr name)] pprCtO (OverLabelOrigin l) = hsep [text "the overloaded label" ,quotes (char '#' <> ppr l)] pprCtO RecordUpdOrigin = text "a record update" pprCtO ExprSigOrigin = text "an expression type signature" pprCtO PatSigOrigin = text "a pattern type signature" pprCtO PatOrigin = text "a pattern" pprCtO ViewPatOrigin = text "a view pattern" pprCtO IfOrigin = text "an if expression" pprCtO (LiteralOrigin lit) = hsep [text "the literal", quotes (ppr lit)] pprCtO (ArithSeqOrigin seq) = hsep [text "the arithmetic sequence", quotes (ppr seq)] pprCtO (PArrSeqOrigin seq) = hsep [text "the parallel array sequence", quotes (ppr seq)] pprCtO SectionOrigin = text "an operator section" pprCtO TupleOrigin = text "a tuple" pprCtO NegateOrigin = text "a use of syntactic negation" pprCtO (ScOrigin n) = text "the superclasses of an instance declaration" <> ifPprDebug (parens (ppr n)) pprCtO DerivOrigin = text "the 'deriving' clause of a data type declaration" pprCtO StandAloneDerivOrigin = text "a 'deriving' declaration" pprCtO DefaultOrigin = text "a 'default' declaration" pprCtO DoOrigin = text "a do statement" pprCtO MCompOrigin = text "a statement in a monad comprehension" pprCtO ProcOrigin = text "a proc expression" pprCtO (TypeEqOrigin t1 t2 _)= text "a type equality" <+> sep [ppr t1, char '~', ppr t2] pprCtO AnnOrigin = text "an annotation" pprCtO HoleOrigin = text "a use of" <+> quotes (text "_") pprCtO ListOrigin = text "an overloaded list" pprCtO StaticOrigin = text "a static form" pprCtO _ = panic "pprCtOrigin" {- Constraint Solver Plugins ------------------------- -} type TcPluginSolver = [Ct] -- given -> [Ct] -- derived -> [Ct] -- wanted -> TcPluginM TcPluginResult newtype TcPluginM a = TcPluginM (Maybe EvBindsVar -> TcM a) instance Functor TcPluginM where fmap = liftM instance Applicative TcPluginM where pure x = TcPluginM (const $ pure x) (<*>) = ap instance Monad TcPluginM where return = pure fail x = TcPluginM (const $ fail x) TcPluginM m >>= k = TcPluginM (\ ev -> do a <- m ev runTcPluginM (k a) ev) #if __GLASGOW_HASKELL__ > 710 instance MonadFail.MonadFail TcPluginM where fail x = TcPluginM (const $ fail x) #endif runTcPluginM :: TcPluginM a -> Maybe EvBindsVar -> TcM a runTcPluginM (TcPluginM m) = m -- | This function provides an escape for direct access to -- the 'TcM` monad. It should not be used lightly, and -- the provided 'TcPluginM' API should be favoured instead. unsafeTcPluginTcM :: TcM a -> TcPluginM a unsafeTcPluginTcM = TcPluginM . const -- | Access the 'EvBindsVar' carried by the 'TcPluginM' during -- constraint solving. Returns 'Nothing' if invoked during -- 'tcPluginInit' or 'tcPluginStop'. getEvBindsTcPluginM_maybe :: TcPluginM (Maybe EvBindsVar) getEvBindsTcPluginM_maybe = TcPluginM return data TcPlugin = forall s. TcPlugin { tcPluginInit :: TcPluginM s -- ^ Initialize plugin, when entering type-checker. , tcPluginSolve :: s -> TcPluginSolver -- ^ Solve some constraints. -- TODO: WRITE MORE DETAILS ON HOW THIS WORKS. , tcPluginStop :: s -> TcPluginM () -- ^ Clean up after the plugin, when exiting the type-checker. } data TcPluginResult = TcPluginContradiction [Ct] -- ^ The plugin found a contradiction. -- The returned constraints are removed from the inert set, -- and recorded as insoluable. | TcPluginOk [(EvTerm,Ct)] [Ct] -- ^ The first field is for constraints that were solved. -- These are removed from the inert set, -- and the evidence for them is recorded. -- The second field contains new work, that should be processed by -- the constraint solver.