2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 The @Inst@ type: dictionaries or method instances
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
19 pprInstances, pprDictsTheta, pprDictsInFull, -- User error messages
20 showLIE, pprInst, pprInsts, pprInstInFull, -- Debugging messages
22 tidyInsts, tidyMoreInsts,
24 newDictBndr, newDictBndrs, newDictBndrsO,
25 instCall, instStupidTheta,
27 shortCutFracLit, shortCutIntLit, shortCutStringLit, newIPDict,
28 newMethod, newMethodFromName, newMethodWithGivenTy,
30 tcSyntaxName, isHsVar,
32 tyVarsOfInst, tyVarsOfInsts, tyVarsOfLIE,
33 ipNamesOfInst, ipNamesOfInsts, fdPredsOfInst, fdPredsOfInsts,
34 getDictClassTys, dictPred,
36 lookupSimpleInst, LookupInstResult(..),
37 tcExtendLocalInstEnv, tcGetInstEnvs, getOverlapFlag,
39 isAbstractableInst, isEqInst,
40 isDict, isClassDict, isMethod, isImplicInst,
41 isIPDict, isInheritableInst, isMethodOrLit,
42 isTyVarDict, isMethodFor,
45 instToId, instToVar, instType, instName, instToDictBind,
48 InstOrigin(..), InstLoc, pprInstLoc,
50 mkWantedCo, mkGivenCo,
51 fromWantedCo, fromGivenCo,
52 eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst,
53 finalizeEqInst, writeWantedCoercion,
54 eqInstType, updateEqInstCoercion,
55 eqInstCoercion, eqInstTys
58 #include "HsVersions.h"
60 import {-# SOURCE #-} TcExpr( tcPolyExpr )
61 import {-# SOURCE #-} TcUnify( boxyUnify, unifyType )
63 import FastString(FastString)
85 import Var ( Var, TyVar )
110 instName :: Inst -> Name
111 instName (EqInst {tci_name = name}) = name
112 instName inst = Var.varName (instToVar inst)
114 instToId :: Inst -> TcId
115 instToId inst = WARN( not (isId id), ppr inst )
120 instToVar :: Inst -> Var
121 instToVar (LitInst {tci_name = nm, tci_ty = ty})
123 instToVar (Method {tci_id = id})
125 instToVar (Dict {tci_name = nm, tci_pred = pred})
126 | isEqPred pred = Var.mkCoVar nm (mkPredTy pred)
127 | otherwise = mkLocalId nm (mkPredTy pred)
128 instToVar (ImplicInst {tci_name = nm, tci_tyvars = tvs, tci_given = givens,
129 tci_wanted = wanteds})
130 = mkLocalId nm (mkImplicTy tvs givens wanteds)
131 instToVar i@(EqInst {})
132 = eitherEqInst i id (\(TyVarTy covar) -> covar)
134 instType :: Inst -> Type
135 instType (LitInst {tci_ty = ty}) = ty
136 instType (Method {tci_id = id}) = idType id
137 instType (Dict {tci_pred = pred}) = mkPredTy pred
138 instType imp@(ImplicInst {}) = mkImplicTy (tci_tyvars imp) (tci_given imp)
140 -- instType i@(EqInst {tci_co = co}) = eitherEqInst i TyVarTy id
141 instType (EqInst {tci_left = ty1, tci_right = ty2}) = mkPredTy (EqPred ty1 ty2)
143 mkImplicTy tvs givens wanteds -- The type of an implication constraint
144 = ASSERT( all isAbstractableInst givens )
145 -- pprTrace "mkImplicTy" (ppr givens) $
146 -- See [Equational Constraints in Implication Constraints]
147 let dict_wanteds = filter (not . isEqInst) wanteds
150 mkPhiTy (map dictPred givens) $
151 if isSingleton dict_wanteds then
152 instType (head dict_wanteds)
154 mkTupleTy Boxed (length dict_wanteds) (map instType dict_wanteds)
156 dictPred (Dict {tci_pred = pred}) = pred
157 dictPred (EqInst {tci_left=ty1,tci_right=ty2}) = EqPred ty1 ty2
158 dictPred inst = pprPanic "dictPred" (ppr inst)
160 getDictClassTys (Dict {tci_pred = pred}) = getClassPredTys pred
161 getDictClassTys inst = pprPanic "getDictClassTys" (ppr inst)
163 -- fdPredsOfInst is used to get predicates that contain functional
164 -- dependencies *or* might do so. The "might do" part is because
165 -- a constraint (C a b) might have a superclass with FDs
166 -- Leaving these in is really important for the call to fdPredsOfInsts
167 -- in TcSimplify.inferLoop, because the result is fed to 'grow',
168 -- which is supposed to be conservative
169 fdPredsOfInst (Dict {tci_pred = pred}) = [pred]
170 fdPredsOfInst (Method {tci_theta = theta}) = theta
171 fdPredsOfInst (ImplicInst {tci_given = gs,
172 tci_wanted = ws}) = fdPredsOfInsts (gs ++ ws)
173 fdPredsOfInst (LitInst {}) = []
174 fdPredsOfInst (EqInst {}) = []
176 fdPredsOfInsts :: [Inst] -> [PredType]
177 fdPredsOfInsts insts = concatMap fdPredsOfInst insts
179 isInheritableInst (Dict {tci_pred = pred}) = isInheritablePred pred
180 isInheritableInst (Method {tci_theta = theta}) = all isInheritablePred theta
181 isInheritableInst other = True
184 ---------------------------------
185 -- Get the implicit parameters mentioned by these Insts
186 -- NB: the results of these functions are insensitive to zonking
188 ipNamesOfInsts :: [Inst] -> [Name]
189 ipNamesOfInst :: Inst -> [Name]
190 ipNamesOfInsts insts = [n | inst <- insts, n <- ipNamesOfInst inst]
192 ipNamesOfInst (Dict {tci_pred = IParam n _}) = [ipNameName n]
193 ipNamesOfInst (Method {tci_theta = theta}) = [ipNameName n | IParam n _ <- theta]
194 ipNamesOfInst other = []
196 ---------------------------------
197 tyVarsOfInst :: Inst -> TcTyVarSet
198 tyVarsOfInst (LitInst {tci_ty = ty}) = tyVarsOfType ty
199 tyVarsOfInst (Dict {tci_pred = pred}) = tyVarsOfPred pred
200 tyVarsOfInst (Method {tci_oid = id, tci_tys = tys}) = tyVarsOfTypes tys `unionVarSet` varTypeTyVars id
201 -- The id might have free type variables; in the case of
202 -- locally-overloaded class methods, for example
203 tyVarsOfInst (ImplicInst {tci_tyvars = tvs, tci_given = givens, tci_wanted = wanteds})
204 = (tyVarsOfInsts givens `unionVarSet` tyVarsOfInsts wanteds)
205 `minusVarSet` mkVarSet tvs
206 `unionVarSet` unionVarSets (map varTypeTyVars tvs)
207 -- Remember the free tyvars of a coercion
208 tyVarsOfInst (EqInst {tci_left = ty1, tci_right = ty2}) = tyVarsOfType ty1 `unionVarSet` tyVarsOfType ty2
210 tyVarsOfInsts insts = foldr (unionVarSet . tyVarsOfInst) emptyVarSet insts
211 tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie)
214 --------------------------
215 instToDictBind :: Inst -> LHsExpr TcId -> TcDictBinds
216 instToDictBind inst rhs
217 = unitBag (L (instSpan inst) (VarBind (instToId inst) rhs))
219 addInstToDictBind :: TcDictBinds -> Inst -> LHsExpr TcId -> TcDictBinds
220 addInstToDictBind binds inst rhs = binds `unionBags` instToDictBind inst rhs
227 isAbstractableInst :: Inst -> Bool
228 isAbstractableInst inst = isDict inst || isEqInst inst
230 isEqInst :: Inst -> Bool
231 isEqInst (EqInst {}) = True
232 isEqInst other = False
234 isDict :: Inst -> Bool
235 isDict (Dict {}) = True
238 isClassDict :: Inst -> Bool
239 isClassDict (Dict {tci_pred = pred}) = isClassPred pred
240 isClassDict other = False
242 isTyVarDict :: Inst -> Bool
243 isTyVarDict (Dict {tci_pred = pred}) = isTyVarClassPred pred
244 isTyVarDict other = False
246 isIPDict :: Inst -> Bool
247 isIPDict (Dict {tci_pred = pred}) = isIPPred pred
248 isIPDict other = False
250 isImplicInst (ImplicInst {}) = True
251 isImplicInst other = False
253 isMethod :: Inst -> Bool
254 isMethod (Method {}) = True
255 isMethod other = False
257 isMethodFor :: TcIdSet -> Inst -> Bool
258 isMethodFor ids (Method {tci_oid = id}) = id `elemVarSet` ids
259 isMethodFor ids inst = False
261 isMethodOrLit :: Inst -> Bool
262 isMethodOrLit (Method {}) = True
263 isMethodOrLit (LitInst {}) = True
264 isMethodOrLit other = False
268 %************************************************************************
270 \subsection{Building dictionaries}
272 %************************************************************************
274 -- newDictBndrs makes a dictionary at a binding site
275 -- instCall makes a dictionary at an occurrence site
276 -- and throws it into the LIE
280 newDictBndrsO :: InstOrigin -> TcThetaType -> TcM [Inst]
281 newDictBndrsO orig theta = do { loc <- getInstLoc orig
282 ; newDictBndrs loc theta }
284 newDictBndrs :: InstLoc -> TcThetaType -> TcM [Inst]
285 newDictBndrs inst_loc theta = mapM (newDictBndr inst_loc) theta
287 newDictBndr :: InstLoc -> TcPredType -> TcM Inst
288 newDictBndr inst_loc pred@(EqPred ty1 ty2)
289 = do { uniq <- newUnique
290 ; let name = mkPredName uniq inst_loc pred
291 ; return (EqInst {tci_name = name,
295 tci_co = mkGivenCo $ TyVarTy (Var.mkCoVar name (PredTy pred))})
297 newDictBndr inst_loc pred
298 = do { uniq <- newUnique
299 ; let name = mkPredName uniq inst_loc pred
300 ; return (Dict {tci_name = name, tci_pred = pred, tci_loc = inst_loc}) }
303 instCall :: InstOrigin -> [TcType] -> TcThetaType -> TcM HsWrapper
304 -- Instantiate the constraints of a call
305 -- (instCall o tys theta)
306 -- (a) Makes fresh dictionaries as necessary for the constraints (theta)
307 -- (b) Throws these dictionaries into the LIE
308 -- (c) Returns an HsWrapper ([.] tys dicts)
310 instCall orig tys theta
311 = do { loc <- getInstLoc orig
312 ; dict_app <- instCallDicts loc theta
313 ; return (dict_app <.> mkWpTyApps tys) }
316 instStupidTheta :: InstOrigin -> TcThetaType -> TcM ()
317 -- Similar to instCall, but only emit the constraints in the LIE
318 -- Used exclusively for the 'stupid theta' of a data constructor
319 instStupidTheta orig theta
320 = do { loc <- getInstLoc orig
321 ; _co <- instCallDicts loc theta -- Discard the coercion
325 instCallDicts :: InstLoc -> TcThetaType -> TcM HsWrapper
326 -- Instantiates the TcTheta, puts all constraints thereby generated
327 -- into the LIE, and returns a HsWrapper to enclose the call site.
328 -- This is the key place where equality predicates
329 -- are unleashed into the world
330 instCallDicts loc [] = return idHsWrapper
332 -- instCallDicts loc (EqPred ty1 ty2 : preds)
333 -- = do { unifyType ty1 ty2 -- For now, we insist that they unify right away
334 -- -- Later on, when we do associated types,
335 -- -- unifyType :: Type -> Type -> TcM ([Inst], Coercion)
336 -- ; (dicts, co_fn) <- instCallDicts loc preds
337 -- ; return (dicts, co_fn <.> WpTyApp ty1) }
338 -- -- We use type application to apply the function to the
339 -- -- coercion; here ty1 *is* the appropriate identity coercion
341 instCallDicts loc (EqPred ty1 ty2 : preds)
342 = do { traceTc (text "instCallDicts" <+> ppr (EqPred ty1 ty2))
343 ; coi <- boxyUnify ty1 ty2
344 -- ; coi <- unifyType ty1 ty2
345 ; let co = fromCoI coi ty1
346 ; co_fn <- instCallDicts loc preds
347 ; return (co_fn <.> WpTyApp co) }
349 instCallDicts loc (pred : preds)
350 = do { uniq <- newUnique
351 ; let name = mkPredName uniq loc pred
352 dict = Dict {tci_name = name, tci_pred = pred, tci_loc = loc}
354 ; co_fn <- instCallDicts loc preds
355 ; return (co_fn <.> WpApp (instToId dict)) }
358 cloneDict :: Inst -> TcM Inst
359 cloneDict dict@(Dict nm ty loc) = do { uniq <- newUnique
360 ; return (dict {tci_name = setNameUnique nm uniq}) }
361 cloneDict eq@(EqInst {}) = return eq
362 cloneDict other = pprPanic "cloneDict" (ppr other)
364 -- For vanilla implicit parameters, there is only one in scope
365 -- at any time, so we used to use the name of the implicit parameter itself
366 -- But with splittable implicit parameters there may be many in
367 -- scope, so we make up a new namea.
368 newIPDict :: InstOrigin -> IPName Name -> Type
369 -> TcM (IPName Id, Inst)
370 newIPDict orig ip_name ty = do
371 inst_loc <- getInstLoc orig
374 pred = IParam ip_name ty
375 name = mkPredName uniq inst_loc pred
376 dict = Dict {tci_name = name, tci_pred = pred, tci_loc = inst_loc}
378 return (mapIPName (\n -> instToId dict) ip_name, dict)
383 mkPredName :: Unique -> InstLoc -> PredType -> Name
384 mkPredName uniq loc pred_ty
385 = mkInternalName uniq occ (instLocSpan loc)
387 occ = case pred_ty of
388 ClassP cls _ -> mkDictOcc (getOccName cls)
389 IParam ip _ -> getOccName (ipNameName ip)
390 EqPred ty _ -> mkEqPredCoOcc baseOcc
392 -- we use the outermost tycon of the lhs, if there is one, to
393 -- improve readability of Core code
394 baseOcc = case splitTyConApp_maybe ty of
395 Nothing -> mkOccName tcName "$"
396 Just (tc, _) -> getOccName tc
399 %************************************************************************
401 \subsection{Building methods (calls of overloaded functions)}
403 %************************************************************************
407 newMethodFromName :: InstOrigin -> BoxyRhoType -> Name -> TcM TcId
408 newMethodFromName origin ty name = do
409 id <- tcLookupId name
410 -- Use tcLookupId not tcLookupGlobalId; the method is almost
411 -- always a class op, but with -fno-implicit-prelude GHC is
412 -- meant to find whatever thing is in scope, and that may
413 -- be an ordinary function.
414 loc <- getInstLoc origin
415 inst <- tcInstClassOp loc id [ty]
417 return (instToId inst)
419 newMethodWithGivenTy orig id tys = do
420 loc <- getInstLoc orig
421 inst <- newMethod loc id tys
423 return (instToId inst)
425 --------------------------------------------
426 -- tcInstClassOp, and newMethod do *not* drop the
427 -- Inst into the LIE; they just returns the Inst
428 -- This is important because they are used by TcSimplify
431 -- NB: the kind of the type variable to be instantiated
432 -- might be a sub-kind of the type to which it is applied,
433 -- notably when the latter is a type variable of kind ??
434 -- Hence the call to checkKind
435 -- A worry: is this needed anywhere else?
436 tcInstClassOp :: InstLoc -> Id -> [TcType] -> TcM Inst
437 tcInstClassOp inst_loc sel_id tys = do
439 (tyvars, _rho) = tcSplitForAllTys (idType sel_id)
440 zipWithM_ checkKind tyvars tys
441 newMethod inst_loc sel_id tys
443 checkKind :: TyVar -> TcType -> TcM ()
444 -- Ensure that the type has a sub-kind of the tyvar
447 -- ty1 <- zonkTcType ty
448 ; if typeKind ty1 `isSubKind` Var.tyVarKind tv
452 pprPanic "checkKind: adding kind constraint"
453 (vcat [ppr tv <+> ppr (Var.tyVarKind tv),
454 ppr ty <+> ppr ty1 <+> ppr (typeKind ty1)])
456 -- do { tv1 <- tcInstTyVar tv
457 -- ; unifyType ty1 (mkTyVarTy tv1) } }
460 ---------------------------
461 newMethod inst_loc id tys = do
462 new_uniq <- newUnique
464 (theta,tau) = tcSplitPhiTy (applyTys (idType id) tys)
465 meth_id = mkUserLocal (mkMethodOcc (getOccName id)) new_uniq tau loc
466 inst = Method {tci_id = meth_id, tci_oid = id, tci_tys = tys,
467 tci_theta = theta, tci_loc = inst_loc}
468 loc = instLocSpan inst_loc
474 shortCutIntLit :: Integer -> TcType -> Maybe (HsExpr TcId)
476 | isIntTy ty && inIntRange i -- Short cut for Int
477 = Just (HsLit (HsInt i))
478 | isIntegerTy ty -- Short cut for Integer
479 = Just (HsLit (HsInteger i ty))
480 | otherwise = Nothing
482 shortCutFracLit :: Rational -> TcType -> Maybe (HsExpr TcId)
485 = Just (mk_lit floatDataCon (HsFloatPrim f))
487 = Just (mk_lit doubleDataCon (HsDoublePrim f))
488 | otherwise = Nothing
490 mk_lit con lit = HsApp (nlHsVar (dataConWrapId con)) (nlHsLit lit)
492 shortCutStringLit :: FastString -> TcType -> Maybe (HsExpr TcId)
493 shortCutStringLit s ty
494 | isStringTy ty -- Short cut for String
495 = Just (HsLit (HsString s))
496 | otherwise = Nothing
498 mkIntegerLit :: Integer -> TcM (LHsExpr TcId)
500 integer_ty <- tcMetaTy integerTyConName
502 return (L span $ HsLit (HsInteger i integer_ty))
504 mkRatLit :: Rational -> TcM (LHsExpr TcId)
506 rat_ty <- tcMetaTy rationalTyConName
508 return (L span $ HsLit (HsRat r rat_ty))
510 mkStrLit :: FastString -> TcM (LHsExpr TcId)
512 --string_ty <- tcMetaTy stringTyConName
514 return (L span $ HsLit (HsString s))
516 isHsVar :: HsExpr Name -> Name -> Bool
517 isHsVar (HsVar f) g = f==g
518 isHsVar other g = False
522 %************************************************************************
526 %************************************************************************
528 Zonking makes sure that the instance types are fully zonked.
531 zonkInst :: Inst -> TcM Inst
532 zonkInst dict@(Dict { tci_pred = pred}) = do
533 new_pred <- zonkTcPredType pred
534 return (dict {tci_pred = new_pred})
536 zonkInst meth@(Method {tci_oid = id, tci_tys = tys, tci_theta = theta}) = do
538 -- Essential to zonk the id in case it's a local variable
539 -- Can't use zonkIdOcc because the id might itself be
540 -- an InstId, in which case it won't be in scope
542 new_tys <- zonkTcTypes tys
543 new_theta <- zonkTcThetaType theta
544 return (meth { tci_oid = new_id, tci_tys = new_tys, tci_theta = new_theta })
545 -- No need to zonk the tci_id
547 zonkInst lit@(LitInst {tci_ty = ty}) = do
548 new_ty <- zonkTcType ty
549 return (lit {tci_ty = new_ty})
551 zonkInst implic@(ImplicInst {})
552 = ASSERT( all isImmutableTyVar (tci_tyvars implic) )
553 do { givens' <- zonkInsts (tci_given implic)
554 ; wanteds' <- zonkInsts (tci_wanted implic)
555 ; return (implic {tci_given = givens',tci_wanted = wanteds'}) }
557 zonkInst eqinst@(EqInst {tci_left = ty1, tci_right = ty2})
558 = do { co' <- eitherEqInst eqinst
559 (\covar -> return (mkWantedCo covar))
560 (\co -> liftM mkGivenCo $ zonkTcType co)
561 ; ty1' <- zonkTcType ty1
562 ; ty2' <- zonkTcType ty2
563 ; return (eqinst {tci_co = co', tci_left= ty1', tci_right = ty2' })
566 zonkInsts insts = mapM zonkInst insts
570 %************************************************************************
572 \subsection{Printing}
574 %************************************************************************
576 ToDo: improve these pretty-printing things. The ``origin'' is really only
577 relevant in error messages.
580 instance Outputable Inst where
581 ppr inst = pprInst inst
583 pprDictsTheta :: [Inst] -> SDoc
584 -- Print in type-like fashion (Eq a, Show b)
585 -- The Inst can be an implication constraint, but not a Method or LitInst
586 pprDictsTheta insts = parens (sep (punctuate comma (map (ppr . instType) insts)))
588 pprDictsInFull :: [Inst] -> SDoc
589 -- Print in type-like fashion, but with source location
591 = vcat (map go dicts)
593 go dict = sep [quotes (ppr (instType dict)), nest 2 (pprInstArising dict)]
595 pprInsts :: [Inst] -> SDoc
596 -- Debugging: print the evidence :: type
597 pprInsts insts = brackets (interpp'SP insts)
599 pprInst, pprInstInFull :: Inst -> SDoc
600 -- Debugging: print the evidence :: type
601 pprInst i@(EqInst {tci_left = ty1, tci_right = ty2, tci_co = co})
603 (\covar -> text "Wanted" <+> ppr (TyVarTy covar) <+> dcolon <+> ppr (EqPred ty1 ty2))
604 (\co -> text "Given" <+> ppr co <+> dcolon <+> ppr (EqPred ty1 ty2))
605 pprInst inst = ppr name <> braces (pprUnique (getUnique name)) <+> dcolon
606 <+> (braces (ppr (instType inst) <> implicWantedEqs) $$
607 ifPprDebug implic_stuff)
610 (implic_stuff, implicWantedEqs)
611 | isImplicInst inst = (ppr (tci_reft inst),
613 ppr (filter isEqInst (tci_wanted inst)))
614 | otherwise = (empty, empty)
616 pprInstInFull inst@(EqInst {}) = pprInst inst
617 pprInstInFull inst = sep [quotes (pprInst inst), nest 2 (pprInstArising inst)]
619 tidyInst :: TidyEnv -> Inst -> Inst
620 tidyInst env eq@(EqInst {tci_left = lty, tci_right = rty, tci_co = co}) =
621 eq { tci_left = tidyType env lty
622 , tci_right = tidyType env rty
623 , tci_co = either Left (Right . tidyType env) co
625 tidyInst env lit@(LitInst {tci_ty = ty}) = lit {tci_ty = tidyType env ty}
626 tidyInst env dict@(Dict {tci_pred = pred}) = dict {tci_pred = tidyPred env pred}
627 tidyInst env meth@(Method {tci_tys = tys}) = meth {tci_tys = tidyTypes env tys}
628 tidyInst env implic@(ImplicInst {})
629 = implic { tci_tyvars = tvs'
630 , tci_given = map (tidyInst env') (tci_given implic)
631 , tci_wanted = map (tidyInst env') (tci_wanted implic) }
633 (env', tvs') = mapAccumL tidyTyVarBndr env (tci_tyvars implic)
635 tidyMoreInsts :: TidyEnv -> [Inst] -> (TidyEnv, [Inst])
636 -- This function doesn't assume that the tyvars are in scope
637 -- so it works like tidyOpenType, returning a TidyEnv
638 tidyMoreInsts env insts
639 = (env', map (tidyInst env') insts)
641 env' = tidyFreeTyVars env (tyVarsOfInsts insts)
643 tidyInsts :: [Inst] -> (TidyEnv, [Inst])
644 tidyInsts insts = tidyMoreInsts emptyTidyEnv insts
646 showLIE :: SDoc -> TcM () -- Debugging
648 = do { lie_var <- getLIEVar ;
649 lie <- readMutVar lie_var ;
650 traceTc (str <+> vcat (map pprInstInFull (lieToList lie))) }
654 %************************************************************************
656 Extending the instance environment
658 %************************************************************************
661 tcExtendLocalInstEnv :: [Instance] -> TcM a -> TcM a
662 -- Add new locally-defined instances
663 tcExtendLocalInstEnv dfuns thing_inside
664 = do { traceDFuns dfuns
666 ; inst_env' <- foldlM addLocalInst (tcg_inst_env env) dfuns
667 ; let env' = env { tcg_insts = dfuns ++ tcg_insts env,
668 tcg_inst_env = inst_env' }
669 ; setGblEnv env' thing_inside }
671 addLocalInst :: InstEnv -> Instance -> TcM InstEnv
672 -- Check that the proposed new instance is OK,
673 -- and then add it to the home inst env
674 addLocalInst home_ie ispec
675 = do { -- Instantiate the dfun type so that we extend the instance
676 -- envt with completely fresh template variables
677 -- This is important because the template variables must
678 -- not overlap with anything in the things being looked up
679 -- (since we do unification).
680 -- We use tcInstSkolType because we don't want to allocate fresh
681 -- *meta* type variables.
682 let dfun = instanceDFunId ispec
683 ; (tvs', theta', tau') <- tcInstSkolType InstSkol (idType dfun)
684 ; let (cls, tys') = tcSplitDFunHead tau'
685 dfun' = setIdType dfun (mkSigmaTy tvs' theta' tau')
686 ispec' = setInstanceDFunId ispec dfun'
688 -- Load imported instances, so that we report
689 -- duplicates correctly
691 ; let inst_envs = (eps_inst_env eps, home_ie)
693 -- Check functional dependencies
694 ; case checkFunDeps inst_envs ispec' of
695 Just specs -> funDepErr ispec' specs
698 -- Check for duplicate instance decls
699 ; let { (matches, _) = lookupInstEnv inst_envs cls tys'
700 ; dup_ispecs = [ dup_ispec
701 | (dup_ispec, _) <- matches
702 , let (_,_,_,dup_tys) = instanceHead dup_ispec
703 , isJust (tcMatchTys (mkVarSet tvs') tys' dup_tys)] }
704 -- Find memebers of the match list which ispec itself matches.
705 -- If the match is 2-way, it's a duplicate
707 dup_ispec : _ -> dupInstErr ispec' dup_ispec
710 -- OK, now extend the envt
711 ; return (extendInstEnv home_ie ispec') }
713 getOverlapFlag :: TcM OverlapFlag
715 = do { dflags <- getDOpts
716 ; let overlap_ok = dopt Opt_OverlappingInstances dflags
717 incoherent_ok = dopt Opt_IncoherentInstances dflags
718 overlap_flag | incoherent_ok = Incoherent
719 | overlap_ok = OverlapOk
720 | otherwise = NoOverlap
722 ; return overlap_flag }
725 = traceTc (hang (text "Adding instances:") 2 (vcat (map pp ispecs)))
727 pp ispec = ppr (instanceDFunId ispec) <+> colon <+> ppr ispec
728 -- Print the dfun name itself too
730 funDepErr ispec ispecs
732 addErr (hang (ptext SLIT("Functional dependencies conflict between instance declarations:"))
733 2 (pprInstances (ispec:ispecs)))
734 dupInstErr ispec dup_ispec
736 addErr (hang (ptext SLIT("Duplicate instance declarations:"))
737 2 (pprInstances [ispec, dup_ispec]))
739 addDictLoc ispec thing_inside
740 = setSrcSpan (mkSrcSpan loc loc) thing_inside
742 loc = getSrcLoc ispec
746 %************************************************************************
748 \subsection{Looking up Insts}
750 %************************************************************************
753 data LookupInstResult
755 | GenInst [Inst] (LHsExpr TcId) -- The expression and its needed insts
757 lookupSimpleInst :: Inst -> TcM LookupInstResult
758 -- This is "simple" in that it returns NoInstance for implication constraints
760 -- It's important that lookupInst does not put any new stuff into
761 -- the LIE. Instead, any Insts needed by the lookup are returned in
762 -- the LookupInstResult, where they can be further processed by tcSimplify
764 lookupSimpleInst (EqInst {}) = return NoInstance
766 --------------------- Implications ------------------------
767 lookupSimpleInst (ImplicInst {}) = return NoInstance
769 --------------------- Methods ------------------------
770 lookupSimpleInst (Method {tci_oid = id, tci_tys = tys, tci_theta = theta, tci_loc = loc})
771 = do { (dict_app, dicts) <- getLIE $ instCallDicts loc theta
772 ; let co_fn = dict_app <.> mkWpTyApps tys
773 ; return (GenInst dicts (L span $ HsWrap co_fn (HsVar id))) }
775 span = instLocSpan loc
777 --------------------- Literals ------------------------
778 -- Look for short cuts first: if the literal is *definitely* a
779 -- int, integer, float or a double, generate the real thing here.
780 -- This is essential (see nofib/spectral/nucleic).
781 -- [Same shortcut as in newOverloadedLit, but we
782 -- may have done some unification by now]
784 lookupSimpleInst (LitInst {tci_lit = HsIntegral i from_integer_name _, tci_ty = ty, tci_loc = loc})
785 | Just expr <- shortCutIntLit i ty
786 = return (GenInst [] (noLoc expr))
788 = ASSERT( from_integer_name `isHsVar` fromIntegerName ) do -- A LitInst invariant
789 from_integer <- tcLookupId fromIntegerName
790 method_inst <- tcInstClassOp loc from_integer [ty]
791 integer_lit <- mkIntegerLit i
792 return (GenInst [method_inst]
793 (mkHsApp (L (instLocSpan loc)
794 (HsVar (instToId method_inst))) integer_lit))
796 lookupSimpleInst (LitInst {tci_lit = HsFractional f from_rat_name _, tci_ty = ty, tci_loc = loc})
797 | Just expr <- shortCutFracLit f ty
798 = return (GenInst [] (noLoc expr))
801 = ASSERT( from_rat_name `isHsVar` fromRationalName ) do -- A LitInst invariant
802 from_rational <- tcLookupId fromRationalName
803 method_inst <- tcInstClassOp loc from_rational [ty]
804 rat_lit <- mkRatLit f
805 return (GenInst [method_inst] (mkHsApp (L (instLocSpan loc)
806 (HsVar (instToId method_inst))) rat_lit))
808 lookupSimpleInst (LitInst {tci_lit = HsIsString s from_string_name _, tci_ty = ty, tci_loc = loc})
809 | Just expr <- shortCutStringLit s ty
810 = return (GenInst [] (noLoc expr))
812 = ASSERT( from_string_name `isHsVar` fromStringName ) do -- A LitInst invariant
813 from_string <- tcLookupId fromStringName
814 method_inst <- tcInstClassOp loc from_string [ty]
815 string_lit <- mkStrLit s
816 return (GenInst [method_inst]
817 (mkHsApp (L (instLocSpan loc)
818 (HsVar (instToId method_inst))) string_lit))
820 --------------------- Dictionaries ------------------------
821 lookupSimpleInst (Dict {tci_pred = pred, tci_loc = loc})
822 = do { mb_result <- lookupPred pred
823 ; case mb_result of {
824 Nothing -> return NoInstance ;
825 Just (dfun_id, mb_inst_tys) -> do
827 { use_stage <- getStage
828 ; checkWellStaged (ptext SLIT("instance for") <+> quotes (ppr pred))
829 (topIdLvl dfun_id) use_stage
831 -- It's possible that not all the tyvars are in
832 -- the substitution, tenv. For example:
833 -- instance C X a => D X where ...
834 -- (presumably there's a functional dependency in class C)
835 -- Hence mb_inst_tys :: Either TyVar TcType
837 ; let inst_tv (Left tv) = do { tv' <- tcInstTyVar tv; return (mkTyVarTy tv') }
838 inst_tv (Right ty) = return ty
839 ; tys <- mapM inst_tv mb_inst_tys
841 (theta, _) = tcSplitPhiTy (applyTys (idType dfun_id) tys)
842 src_loc = instLocSpan loc
845 return (GenInst [] (L src_loc $ HsWrap (mkWpTyApps tys) dfun))
847 { (dict_app, dicts) <- getLIE $ instCallDicts loc theta -- !!!
848 ; let co_fn = dict_app <.> mkWpTyApps tys
849 ; return (GenInst dicts (L src_loc $ HsWrap co_fn dfun))
853 lookupPred :: TcPredType -> TcM (Maybe (DFunId, [Either TyVar TcType]))
854 -- Look up a class constraint in the instance environment
855 lookupPred pred@(ClassP clas tys)
857 ; tcg_env <- getGblEnv
858 ; let inst_envs = (eps_inst_env eps, tcg_inst_env tcg_env)
859 ; case lookupInstEnv inst_envs clas tys of {
860 ([(ispec, inst_tys)], [])
861 -> do { let dfun_id = is_dfun ispec
862 ; traceTc (text "lookupInst success" <+>
863 vcat [text "dict" <+> ppr pred,
864 text "witness" <+> ppr dfun_id
865 <+> ppr (idType dfun_id) ])
866 -- Record that this dfun is needed
867 ; record_dfun_usage dfun_id
868 ; return (Just (dfun_id, inst_tys)) } ;
871 -> do { traceTc (text "lookupInst fail" <+>
872 vcat [text "dict" <+> ppr pred,
873 text "matches" <+> ppr matches,
874 text "unifs" <+> ppr unifs])
875 -- In the case of overlap (multiple matches) we report
876 -- NoInstance here. That has the effect of making the
877 -- context-simplifier return the dict as an irreducible one.
878 -- Then it'll be given to addNoInstanceErrs, which will do another
879 -- lookupInstEnv to get the detailed info about what went wrong.
883 lookupPred ip_pred = return Nothing -- Implicit parameters
885 record_dfun_usage dfun_id
886 = do { hsc_env <- getTopEnv
887 ; let dfun_name = idName dfun_id
888 dfun_mod = nameModule dfun_name
889 ; if isInternalName dfun_name || -- Internal name => defined in this module
890 modulePackageId dfun_mod /= thisPackage (hsc_dflags hsc_env)
891 then return () -- internal, or in another package
892 else do { tcg_env <- getGblEnv
893 ; updMutVar (tcg_inst_uses tcg_env)
894 (`addOneToNameSet` idName dfun_id) }}
897 tcGetInstEnvs :: TcM (InstEnv, InstEnv)
898 -- Gets both the external-package inst-env
899 -- and the home-pkg inst env (includes module being compiled)
900 tcGetInstEnvs = do { eps <- getEps; env <- getGblEnv;
901 return (eps_inst_env eps, tcg_inst_env env) }
906 %************************************************************************
910 %************************************************************************
912 Suppose we are doing the -fno-implicit-prelude thing, and we encounter
913 a do-expression. We have to find (>>) in the current environment, which is
914 done by the rename. Then we have to check that it has the same type as
915 Control.Monad.(>>). Or, more precisely, a compatible type. One 'customer' had
918 (>>) :: HB m n mn => m a -> n b -> mn b
920 So the idea is to generate a local binding for (>>), thus:
922 let then72 :: forall a b. m a -> m b -> m b
923 then72 = ...something involving the user's (>>)...
925 ...the do-expression...
927 Now the do-expression can proceed using then72, which has exactly
930 In fact tcSyntaxName just generates the RHS for then72, because we only
931 want an actual binding in the do-expression case. For literals, we can
932 just use the expression inline.
935 tcSyntaxName :: InstOrigin
936 -> TcType -- Type to instantiate it at
937 -> (Name, HsExpr Name) -- (Standard name, user name)
938 -> TcM (Name, HsExpr TcId) -- (Standard name, suitable expression)
939 -- *** NOW USED ONLY FOR CmdTop (sigh) ***
940 -- NB: tcSyntaxName calls tcExpr, and hence can do unification.
941 -- So we do not call it from lookupInst, which is called from tcSimplify
943 tcSyntaxName orig ty (std_nm, HsVar user_nm)
945 = do id <- newMethodFromName orig ty std_nm
946 return (std_nm, HsVar id)
948 tcSyntaxName orig ty (std_nm, user_nm_expr) = do
949 std_id <- tcLookupId std_nm
951 -- C.f. newMethodAtLoc
952 ([tv], _, tau) = tcSplitSigmaTy (idType std_id)
953 sigma1 = substTyWith [tv] [ty] tau
954 -- Actually, the "tau-type" might be a sigma-type in the
955 -- case of locally-polymorphic methods.
957 addErrCtxtM (syntaxNameCtxt user_nm_expr orig sigma1) $ do
959 -- Check that the user-supplied thing has the
960 -- same type as the standard one.
961 -- Tiresome jiggling because tcCheckSigma takes a located expression
963 expr <- tcPolyExpr (L span user_nm_expr) sigma1
964 return (std_nm, unLoc expr)
966 syntaxNameCtxt name orig ty tidy_env = do
967 inst_loc <- getInstLoc orig
969 msg = vcat [ptext SLIT("When checking that") <+> quotes (ppr name) <+>
970 ptext SLIT("(needed by a syntactic construct)"),
971 nest 2 (ptext SLIT("has the required type:") <+> ppr (tidyType tidy_env ty)),
972 nest 2 (ptext SLIT("arising from") <+> pprInstLoc inst_loc)]
974 return (tidy_env, msg)
977 %************************************************************************
981 %************************************************************************
984 mkGivenCo :: Coercion -> Either TcTyVar Coercion
987 mkWantedCo :: TcTyVar -> Either TcTyVar Coercion
990 fromGivenCo :: Either TcTyVar Coercion -> Coercion
991 fromGivenCo (Right co) = co
992 fromGivenCo _ = panic "fromGivenCo: not a wanted coercion"
994 fromWantedCo :: String -> Either TcTyVar Coercion -> TcTyVar
995 fromWantedCo _ (Left covar) = covar
996 fromWantedCo msg _ = panic ("fromWantedCo: not a wanted coercion: " ++ msg)
998 eitherEqInst :: Inst -- given or wanted EqInst
999 -> (TcTyVar -> a) -- result if wanted
1000 -> (Coercion -> a) -- result if given
1002 eitherEqInst (EqInst {tci_co = either_co}) withWanted withGiven
1004 Left covar -> withWanted covar
1005 Right co -> withGiven co
1007 mkEqInsts :: [PredType] -> [Either TcTyVar Coercion] -> TcM [Inst]
1008 mkEqInsts preds cos = zipWithM mkEqInst preds cos
1010 mkEqInst :: PredType -> Either TcTyVar Coercion -> TcM Inst
1011 mkEqInst (EqPred ty1 ty2) co
1012 = do { uniq <- newUnique
1013 ; src_span <- getSrcSpanM
1014 ; err_ctxt <- getErrCtxt
1015 ; let loc = InstLoc EqOrigin src_span err_ctxt
1016 name = mkName uniq src_span
1017 inst = EqInst {tci_left = ty1, tci_right = ty2, tci_co = co, tci_loc = loc, tci_name = name}
1020 where mkName uniq src_span = mkInternalName uniq (mkVarOcc "co") src_span
1022 mkWantedEqInst :: PredType -> TcM Inst
1023 mkWantedEqInst pred@(EqPred ty1 ty2)
1024 = do { cotv <- newMetaCoVar ty1 ty2
1025 ; mkEqInst pred (Left cotv)
1029 -- We want to promote the wanted EqInst to a given EqInst
1030 -- in the signature context.
1031 -- This means we have to give the coercion a name
1032 -- and fill it in as its own name.
1035 -> TcM Inst -- given
1036 finalizeEqInst wanted@(EqInst {tci_left = ty1, tci_right = ty2, tci_name = name})
1037 = do { let var = Var.mkCoVar name (PredTy $ EqPred ty1 ty2)
1038 ; writeWantedCoercion wanted (TyVarTy var)
1039 ; let given = wanted { tci_co = mkGivenCo $ TyVarTy var }
1044 :: Inst -- wanted EqInst
1045 -> Coercion -- coercion to fill the hole with
1047 writeWantedCoercion wanted co
1048 = do { let cotv = fromWantedCo "writeWantedCoercion" $ tci_co wanted
1049 ; writeMetaTyVar cotv co
1052 eqInstType :: Inst -> TcType
1053 eqInstType inst = eitherEqInst inst mkTyVarTy id
1055 eqInstCoercion :: Inst -> Either TcTyVar Coercion
1056 eqInstCoercion = tci_co
1058 eqInstTys :: Inst -> (TcType, TcType)
1059 eqInstTys inst = (tci_left inst, tci_right inst)
1061 updateEqInstCoercion :: (Either TcTyVar Coercion -> Either TcTyVar Coercion) -> Inst -> Inst
1062 updateEqInstCoercion f inst = inst {tci_co = f $ tci_co inst}