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 )
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 = Just (HsLit (HsInt i))
477 | isIntegerTy ty = Just (HsLit (HsInteger i ty))
478 | otherwise = shortCutFracLit (fromInteger i) ty
479 -- The 'otherwise' case is important
480 -- Consider (3 :: Float). Syntactically it looks like an IntLit,
481 -- so we'll call shortCutIntLit, but of course it's a float
482 -- This can make a big difference for programs with a lot of
483 -- literals, compiled without -O
485 shortCutFracLit :: Rational -> TcType -> Maybe (HsExpr TcId)
487 | isFloatTy ty = Just (mk_lit floatDataCon (HsFloatPrim f))
488 | isDoubleTy ty = Just (mk_lit doubleDataCon (HsDoublePrim f))
489 | otherwise = Nothing
491 mk_lit con lit = HsApp (nlHsVar (dataConWrapId con)) (nlHsLit lit)
493 shortCutStringLit :: FastString -> TcType -> Maybe (HsExpr TcId)
494 shortCutStringLit s ty
495 | isStringTy ty -- Short cut for String
496 = Just (HsLit (HsString s))
497 | otherwise = Nothing
499 mkIntegerLit :: Integer -> TcM (LHsExpr TcId)
501 integer_ty <- tcMetaTy integerTyConName
503 return (L span $ HsLit (HsInteger i integer_ty))
505 mkRatLit :: Rational -> TcM (LHsExpr TcId)
507 rat_ty <- tcMetaTy rationalTyConName
509 return (L span $ HsLit (HsRat r rat_ty))
511 mkStrLit :: FastString -> TcM (LHsExpr TcId)
513 --string_ty <- tcMetaTy stringTyConName
515 return (L span $ HsLit (HsString s))
517 isHsVar :: HsExpr Name -> Name -> Bool
518 isHsVar (HsVar f) g = f==g
519 isHsVar other g = False
523 %************************************************************************
527 %************************************************************************
529 Zonking makes sure that the instance types are fully zonked.
532 zonkInst :: Inst -> TcM Inst
533 zonkInst dict@(Dict { tci_pred = pred}) = do
534 new_pred <- zonkTcPredType pred
535 return (dict {tci_pred = new_pred})
537 zonkInst meth@(Method {tci_oid = id, tci_tys = tys, tci_theta = theta}) = do
539 -- Essential to zonk the id in case it's a local variable
540 -- Can't use zonkIdOcc because the id might itself be
541 -- an InstId, in which case it won't be in scope
543 new_tys <- zonkTcTypes tys
544 new_theta <- zonkTcThetaType theta
545 return (meth { tci_oid = new_id, tci_tys = new_tys, tci_theta = new_theta })
546 -- No need to zonk the tci_id
548 zonkInst lit@(LitInst {tci_ty = ty}) = do
549 new_ty <- zonkTcType ty
550 return (lit {tci_ty = new_ty})
552 zonkInst implic@(ImplicInst {})
553 = ASSERT( all isImmutableTyVar (tci_tyvars implic) )
554 do { givens' <- zonkInsts (tci_given implic)
555 ; wanteds' <- zonkInsts (tci_wanted implic)
556 ; return (implic {tci_given = givens',tci_wanted = wanteds'}) }
558 zonkInst eqinst@(EqInst {tci_left = ty1, tci_right = ty2})
559 = do { co' <- eitherEqInst eqinst
560 (\covar -> return (mkWantedCo covar))
561 (\co -> liftM mkGivenCo $ zonkTcType co)
562 ; ty1' <- zonkTcType ty1
563 ; ty2' <- zonkTcType ty2
564 ; return (eqinst {tci_co = co', tci_left= ty1', tci_right = ty2' })
567 zonkInsts insts = mapM zonkInst insts
571 %************************************************************************
573 \subsection{Printing}
575 %************************************************************************
577 ToDo: improve these pretty-printing things. The ``origin'' is really only
578 relevant in error messages.
581 instance Outputable Inst where
582 ppr inst = pprInst inst
584 pprDictsTheta :: [Inst] -> SDoc
585 -- Print in type-like fashion (Eq a, Show b)
586 -- The Inst can be an implication constraint, but not a Method or LitInst
587 pprDictsTheta insts = parens (sep (punctuate comma (map (ppr . instType) insts)))
589 pprDictsInFull :: [Inst] -> SDoc
590 -- Print in type-like fashion, but with source location
592 = vcat (map go dicts)
594 go dict = sep [quotes (ppr (instType dict)), nest 2 (pprInstArising dict)]
596 pprInsts :: [Inst] -> SDoc
597 -- Debugging: print the evidence :: type
598 pprInsts insts = brackets (interpp'SP insts)
600 pprInst, pprInstInFull :: Inst -> SDoc
601 -- Debugging: print the evidence :: type
602 pprInst i@(EqInst {tci_left = ty1, tci_right = ty2, tci_co = co})
604 (\covar -> text "Wanted" <+> ppr (TyVarTy covar) <+> dcolon <+> ppr (EqPred ty1 ty2))
605 (\co -> text "Given" <+> ppr co <+> dcolon <+> ppr (EqPred ty1 ty2))
606 pprInst inst = ppr name <> braces (pprUnique (getUnique name)) <+> dcolon
607 <+> braces (ppr (instType inst) <> implicWantedEqs)
611 | isImplicInst inst = text " &" <+>
612 ppr (filter isEqInst (tci_wanted inst))
615 pprInstInFull inst@(EqInst {}) = pprInst inst
616 pprInstInFull inst = sep [quotes (pprInst inst), nest 2 (pprInstArising inst)]
618 tidyInst :: TidyEnv -> Inst -> Inst
619 tidyInst env eq@(EqInst {tci_left = lty, tci_right = rty, tci_co = co}) =
620 eq { tci_left = tidyType env lty
621 , tci_right = tidyType env rty
622 , tci_co = either Left (Right . tidyType env) co
624 tidyInst env lit@(LitInst {tci_ty = ty}) = lit {tci_ty = tidyType env ty}
625 tidyInst env dict@(Dict {tci_pred = pred}) = dict {tci_pred = tidyPred env pred}
626 tidyInst env meth@(Method {tci_tys = tys}) = meth {tci_tys = tidyTypes env tys}
627 tidyInst env implic@(ImplicInst {})
628 = implic { tci_tyvars = tvs'
629 , tci_given = map (tidyInst env') (tci_given implic)
630 , tci_wanted = map (tidyInst env') (tci_wanted implic) }
632 (env', tvs') = mapAccumL tidyTyVarBndr env (tci_tyvars implic)
634 tidyMoreInsts :: TidyEnv -> [Inst] -> (TidyEnv, [Inst])
635 -- This function doesn't assume that the tyvars are in scope
636 -- so it works like tidyOpenType, returning a TidyEnv
637 tidyMoreInsts env insts
638 = (env', map (tidyInst env') insts)
640 env' = tidyFreeTyVars env (tyVarsOfInsts insts)
642 tidyInsts :: [Inst] -> (TidyEnv, [Inst])
643 tidyInsts insts = tidyMoreInsts emptyTidyEnv insts
645 showLIE :: SDoc -> TcM () -- Debugging
647 = do { lie_var <- getLIEVar ;
648 lie <- readMutVar lie_var ;
649 traceTc (str <+> vcat (map pprInstInFull (lieToList lie))) }
653 %************************************************************************
655 Extending the instance environment
657 %************************************************************************
660 tcExtendLocalInstEnv :: [Instance] -> TcM a -> TcM a
661 -- Add new locally-defined instances
662 tcExtendLocalInstEnv dfuns thing_inside
663 = do { traceDFuns dfuns
665 ; inst_env' <- foldlM addLocalInst (tcg_inst_env env) dfuns
666 ; let env' = env { tcg_insts = dfuns ++ tcg_insts env,
667 tcg_inst_env = inst_env' }
668 ; setGblEnv env' thing_inside }
670 addLocalInst :: InstEnv -> Instance -> TcM InstEnv
671 -- Check that the proposed new instance is OK,
672 -- and then add it to the home inst env
673 addLocalInst home_ie ispec
674 = do { -- Instantiate the dfun type so that we extend the instance
675 -- envt with completely fresh template variables
676 -- This is important because the template variables must
677 -- not overlap with anything in the things being looked up
678 -- (since we do unification).
679 -- We use tcInstSkolType because we don't want to allocate fresh
680 -- *meta* type variables.
681 let dfun = instanceDFunId ispec
682 ; (tvs', theta', tau') <- tcInstSkolType InstSkol (idType dfun)
683 ; let (cls, tys') = tcSplitDFunHead tau'
684 dfun' = setIdType dfun (mkSigmaTy tvs' theta' tau')
685 ispec' = setInstanceDFunId ispec dfun'
687 -- Load imported instances, so that we report
688 -- duplicates correctly
690 ; let inst_envs = (eps_inst_env eps, home_ie)
692 -- Check functional dependencies
693 ; case checkFunDeps inst_envs ispec' of
694 Just specs -> funDepErr ispec' specs
697 -- Check for duplicate instance decls
698 ; let { (matches, _) = lookupInstEnv inst_envs cls tys'
699 ; dup_ispecs = [ dup_ispec
700 | (dup_ispec, _) <- matches
701 , let (_,_,_,dup_tys) = instanceHead dup_ispec
702 , isJust (tcMatchTys (mkVarSet tvs') tys' dup_tys)] }
703 -- Find memebers of the match list which ispec itself matches.
704 -- If the match is 2-way, it's a duplicate
706 dup_ispec : _ -> dupInstErr ispec' dup_ispec
709 -- OK, now extend the envt
710 ; return (extendInstEnv home_ie ispec') }
712 getOverlapFlag :: TcM OverlapFlag
714 = do { dflags <- getDOpts
715 ; let overlap_ok = dopt Opt_OverlappingInstances dflags
716 incoherent_ok = dopt Opt_IncoherentInstances dflags
717 overlap_flag | incoherent_ok = Incoherent
718 | overlap_ok = OverlapOk
719 | otherwise = NoOverlap
721 ; return overlap_flag }
724 = traceTc (hang (text "Adding instances:") 2 (vcat (map pp ispecs)))
726 pp ispec = ppr (instanceDFunId ispec) <+> colon <+> ppr ispec
727 -- Print the dfun name itself too
729 funDepErr ispec ispecs
731 addErr (hang (ptext (sLit "Functional dependencies conflict between instance declarations:"))
732 2 (pprInstances (ispec:ispecs)))
733 dupInstErr ispec dup_ispec
735 addErr (hang (ptext (sLit "Duplicate instance declarations:"))
736 2 (pprInstances [ispec, dup_ispec]))
738 addDictLoc ispec thing_inside
739 = setSrcSpan (mkSrcSpan loc loc) thing_inside
741 loc = getSrcLoc ispec
745 %************************************************************************
747 \subsection{Looking up Insts}
749 %************************************************************************
752 data LookupInstResult
754 | GenInst [Inst] (LHsExpr TcId) -- The expression and its needed insts
756 lookupSimpleInst :: Inst -> TcM LookupInstResult
757 -- This is "simple" in that it returns NoInstance for implication constraints
759 -- It's important that lookupInst does not put any new stuff into
760 -- the LIE. Instead, any Insts needed by the lookup are returned in
761 -- the LookupInstResult, where they can be further processed by tcSimplify
763 lookupSimpleInst (EqInst {}) = return NoInstance
765 --------------------- Implications ------------------------
766 lookupSimpleInst (ImplicInst {}) = return NoInstance
768 --------------------- Methods ------------------------
769 lookupSimpleInst (Method {tci_oid = id, tci_tys = tys, tci_theta = theta, tci_loc = loc})
770 = do { (dict_app, dicts) <- getLIE $ instCallDicts loc theta
771 ; let co_fn = dict_app <.> mkWpTyApps tys
772 ; return (GenInst dicts (L span $ HsWrap co_fn (HsVar id))) }
774 span = instLocSpan loc
776 --------------------- Literals ------------------------
777 -- Look for short cuts first: if the literal is *definitely* a
778 -- int, integer, float or a double, generate the real thing here.
779 -- This is essential (see nofib/spectral/nucleic).
780 -- [Same shortcut as in newOverloadedLit, but we
781 -- may have done some unification by now]
783 lookupSimpleInst (LitInst {tci_lit = HsIntegral i from_integer_name _, tci_ty = ty, tci_loc = loc})
784 | Just expr <- shortCutIntLit i ty
785 = return (GenInst [] (noLoc expr))
787 = ASSERT( from_integer_name `isHsVar` fromIntegerName ) do -- A LitInst invariant
788 from_integer <- tcLookupId fromIntegerName
789 method_inst <- tcInstClassOp loc from_integer [ty]
790 integer_lit <- mkIntegerLit i
791 return (GenInst [method_inst]
792 (mkHsApp (L (instLocSpan loc)
793 (HsVar (instToId method_inst))) integer_lit))
795 lookupSimpleInst (LitInst {tci_lit = HsFractional f from_rat_name _, tci_ty = ty, tci_loc = loc})
796 | Just expr <- shortCutFracLit f ty
797 = return (GenInst [] (noLoc expr))
800 = ASSERT( from_rat_name `isHsVar` fromRationalName ) do -- A LitInst invariant
801 from_rational <- tcLookupId fromRationalName
802 method_inst <- tcInstClassOp loc from_rational [ty]
803 rat_lit <- mkRatLit f
804 return (GenInst [method_inst] (mkHsApp (L (instLocSpan loc)
805 (HsVar (instToId method_inst))) rat_lit))
807 lookupSimpleInst (LitInst {tci_lit = HsIsString s from_string_name _, tci_ty = ty, tci_loc = loc})
808 | Just expr <- shortCutStringLit s ty
809 = return (GenInst [] (noLoc expr))
811 = ASSERT( from_string_name `isHsVar` fromStringName ) do -- A LitInst invariant
812 from_string <- tcLookupId fromStringName
813 method_inst <- tcInstClassOp loc from_string [ty]
814 string_lit <- mkStrLit s
815 return (GenInst [method_inst]
816 (mkHsApp (L (instLocSpan loc)
817 (HsVar (instToId method_inst))) string_lit))
819 --------------------- Dictionaries ------------------------
820 lookupSimpleInst (Dict {tci_pred = pred, tci_loc = loc})
821 = do { mb_result <- lookupPred pred
822 ; case mb_result of {
823 Nothing -> return NoInstance ;
824 Just (dfun_id, mb_inst_tys) -> do
826 { use_stage <- getStage
827 ; checkWellStaged (ptext (sLit "instance for") <+> quotes (ppr pred))
828 (topIdLvl dfun_id) use_stage
830 -- It's possible that not all the tyvars are in
831 -- the substitution, tenv. For example:
832 -- instance C X a => D X where ...
833 -- (presumably there's a functional dependency in class C)
834 -- Hence mb_inst_tys :: Either TyVar TcType
836 ; let inst_tv (Left tv) = do { tv' <- tcInstTyVar tv; return (mkTyVarTy tv') }
837 inst_tv (Right ty) = return ty
838 ; tys <- mapM inst_tv mb_inst_tys
840 (theta, _) = tcSplitPhiTy (applyTys (idType dfun_id) tys)
841 src_loc = instLocSpan loc
844 return (GenInst [] (L src_loc $ HsWrap (mkWpTyApps tys) dfun))
846 { (dict_app, dicts) <- getLIE $ instCallDicts loc theta -- !!!
847 ; let co_fn = dict_app <.> mkWpTyApps tys
848 ; return (GenInst dicts (L src_loc $ HsWrap co_fn dfun))
852 lookupPred :: TcPredType -> TcM (Maybe (DFunId, [Either TyVar TcType]))
853 -- Look up a class constraint in the instance environment
854 lookupPred pred@(ClassP clas tys)
856 ; tcg_env <- getGblEnv
857 ; let inst_envs = (eps_inst_env eps, tcg_inst_env tcg_env)
858 ; case lookupInstEnv inst_envs clas tys of {
859 ([(ispec, inst_tys)], [])
860 -> do { let dfun_id = is_dfun ispec
861 ; traceTc (text "lookupInst success" <+>
862 vcat [text "dict" <+> ppr pred,
863 text "witness" <+> ppr dfun_id
864 <+> ppr (idType dfun_id) ])
865 -- Record that this dfun is needed
866 ; record_dfun_usage dfun_id
867 ; return (Just (dfun_id, inst_tys)) } ;
870 -> do { traceTc (text "lookupInst fail" <+>
871 vcat [text "dict" <+> ppr pred,
872 text "matches" <+> ppr matches,
873 text "unifs" <+> ppr unifs])
874 -- In the case of overlap (multiple matches) we report
875 -- NoInstance here. That has the effect of making the
876 -- context-simplifier return the dict as an irreducible one.
877 -- Then it'll be given to addNoInstanceErrs, which will do another
878 -- lookupInstEnv to get the detailed info about what went wrong.
882 lookupPred ip_pred = return Nothing -- Implicit parameters
884 record_dfun_usage dfun_id
885 = do { hsc_env <- getTopEnv
886 ; let dfun_name = idName dfun_id
887 dfun_mod = nameModule dfun_name
888 ; if isInternalName dfun_name || -- Internal name => defined in this module
889 modulePackageId dfun_mod /= thisPackage (hsc_dflags hsc_env)
890 then return () -- internal, or in another package
891 else do { tcg_env <- getGblEnv
892 ; updMutVar (tcg_inst_uses tcg_env)
893 (`addOneToNameSet` idName dfun_id) }}
896 tcGetInstEnvs :: TcM (InstEnv, InstEnv)
897 -- Gets both the external-package inst-env
898 -- and the home-pkg inst env (includes module being compiled)
899 tcGetInstEnvs = do { eps <- getEps; env <- getGblEnv;
900 return (eps_inst_env eps, tcg_inst_env env) }
905 %************************************************************************
909 %************************************************************************
911 Suppose we are doing the -fno-implicit-prelude thing, and we encounter
912 a do-expression. We have to find (>>) in the current environment, which is
913 done by the rename. Then we have to check that it has the same type as
914 Control.Monad.(>>). Or, more precisely, a compatible type. One 'customer' had
917 (>>) :: HB m n mn => m a -> n b -> mn b
919 So the idea is to generate a local binding for (>>), thus:
921 let then72 :: forall a b. m a -> m b -> m b
922 then72 = ...something involving the user's (>>)...
924 ...the do-expression...
926 Now the do-expression can proceed using then72, which has exactly
929 In fact tcSyntaxName just generates the RHS for then72, because we only
930 want an actual binding in the do-expression case. For literals, we can
931 just use the expression inline.
934 tcSyntaxName :: InstOrigin
935 -> TcType -- Type to instantiate it at
936 -> (Name, HsExpr Name) -- (Standard name, user name)
937 -> TcM (Name, HsExpr TcId) -- (Standard name, suitable expression)
938 -- *** NOW USED ONLY FOR CmdTop (sigh) ***
939 -- NB: tcSyntaxName calls tcExpr, and hence can do unification.
940 -- So we do not call it from lookupInst, which is called from tcSimplify
942 tcSyntaxName orig ty (std_nm, HsVar user_nm)
944 = do id <- newMethodFromName orig ty std_nm
945 return (std_nm, HsVar id)
947 tcSyntaxName orig ty (std_nm, user_nm_expr) = do
948 std_id <- tcLookupId std_nm
950 -- C.f. newMethodAtLoc
951 ([tv], _, tau) = tcSplitSigmaTy (idType std_id)
952 sigma1 = substTyWith [tv] [ty] tau
953 -- Actually, the "tau-type" might be a sigma-type in the
954 -- case of locally-polymorphic methods.
956 addErrCtxtM (syntaxNameCtxt user_nm_expr orig sigma1) $ do
958 -- Check that the user-supplied thing has the
959 -- same type as the standard one.
960 -- Tiresome jiggling because tcCheckSigma takes a located expression
962 expr <- tcPolyExpr (L span user_nm_expr) sigma1
963 return (std_nm, unLoc expr)
965 syntaxNameCtxt name orig ty tidy_env = do
966 inst_loc <- getInstLoc orig
968 msg = vcat [ptext (sLit "When checking that") <+> quotes (ppr name) <+>
969 ptext (sLit "(needed by a syntactic construct)"),
970 nest 2 (ptext (sLit "has the required type:") <+> ppr (tidyType tidy_env ty)),
971 nest 2 (ptext (sLit "arising from") <+> pprInstLoc inst_loc)]
973 return (tidy_env, msg)
976 %************************************************************************
980 %************************************************************************
983 mkGivenCo :: Coercion -> Either TcTyVar Coercion
986 mkWantedCo :: TcTyVar -> Either TcTyVar Coercion
989 fromGivenCo :: Either TcTyVar Coercion -> Coercion
990 fromGivenCo (Right co) = co
991 fromGivenCo _ = panic "fromGivenCo: not a wanted coercion"
993 fromWantedCo :: String -> Either TcTyVar Coercion -> TcTyVar
994 fromWantedCo _ (Left covar) = covar
995 fromWantedCo msg _ = panic ("fromWantedCo: not a wanted coercion: " ++ msg)
997 eitherEqInst :: Inst -- given or wanted EqInst
998 -> (TcTyVar -> a) -- result if wanted
999 -> (Coercion -> a) -- result if given
1001 eitherEqInst (EqInst {tci_co = either_co}) withWanted withGiven
1003 Left covar -> withWanted covar
1004 Right co -> withGiven co
1006 mkEqInsts :: [PredType] -> [Either TcTyVar Coercion] -> TcM [Inst]
1007 mkEqInsts preds cos = zipWithM mkEqInst preds cos
1009 mkEqInst :: PredType -> Either TcTyVar Coercion -> TcM Inst
1010 mkEqInst (EqPred ty1 ty2) co
1011 = do { uniq <- newUnique
1012 ; src_span <- getSrcSpanM
1013 ; err_ctxt <- getErrCtxt
1014 ; let loc = InstLoc EqOrigin src_span err_ctxt
1015 name = mkName uniq src_span
1016 inst = EqInst {tci_left = ty1, tci_right = ty2, tci_co = co, tci_loc = loc, tci_name = name}
1019 where mkName uniq src_span = mkInternalName uniq (mkVarOcc "co") src_span
1021 mkWantedEqInst :: PredType -> TcM Inst
1022 mkWantedEqInst pred@(EqPred ty1 ty2)
1023 = do { cotv <- newMetaCoVar ty1 ty2
1024 ; mkEqInst pred (Left cotv)
1028 -- We want to promote the wanted EqInst to a given EqInst
1029 -- in the signature context.
1030 -- This means we have to give the coercion a name
1031 -- and fill it in as its own name.
1034 -> TcM Inst -- given
1035 finalizeEqInst wanted@(EqInst {tci_left = ty1, tci_right = ty2, tci_name = name})
1036 = do { let var = Var.mkCoVar name (PredTy $ EqPred ty1 ty2)
1037 ; writeWantedCoercion wanted (TyVarTy var)
1038 ; let given = wanted { tci_co = mkGivenCo $ TyVarTy var }
1043 :: Inst -- wanted EqInst
1044 -> Coercion -- coercion to fill the hole with
1046 writeWantedCoercion wanted co
1047 = do { let cotv = fromWantedCo "writeWantedCoercion" $ tci_co wanted
1048 ; writeMetaTyVar cotv co
1051 eqInstType :: Inst -> TcType
1052 eqInstType inst = eitherEqInst inst mkTyVarTy id
1054 eqInstCoercion :: Inst -> Either TcTyVar Coercion
1055 eqInstCoercion = tci_co
1057 eqInstTys :: Inst -> (TcType, TcType)
1058 eqInstTys inst = (tci_left inst, tci_right inst)
1060 updateEqInstCoercion :: (Either TcTyVar Coercion -> Either TcTyVar Coercion) -> Inst -> Inst
1061 updateEqInstCoercion f inst = inst {tci_co = f $ tci_co inst}