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 )
102 import Control.Monad ( liftM )
109 instName :: Inst -> Name
110 instName (EqInst {tci_name = name}) = name
111 instName inst = Var.varName (instToVar inst)
113 instToId :: Inst -> TcId
114 instToId inst = WARN( not (isId id), ppr inst )
119 instToVar :: Inst -> Var
120 instToVar (LitInst {tci_name = nm, tci_ty = ty})
122 instToVar (Method {tci_id = id})
124 instToVar (Dict {tci_name = nm, tci_pred = pred})
125 | isEqPred pred = Var.mkCoVar nm (mkPredTy pred)
126 | otherwise = mkLocalId nm (mkPredTy pred)
127 instToVar (ImplicInst {tci_name = nm, tci_tyvars = tvs, tci_given = givens,
128 tci_wanted = wanteds})
129 = mkLocalId nm (mkImplicTy tvs givens wanteds)
130 instToVar i@(EqInst {})
131 = eitherEqInst i id (\(TyVarTy covar) -> covar)
133 instType :: Inst -> Type
134 instType (LitInst {tci_ty = ty}) = ty
135 instType (Method {tci_id = id}) = idType id
136 instType (Dict {tci_pred = pred}) = mkPredTy pred
137 instType imp@(ImplicInst {}) = mkImplicTy (tci_tyvars imp) (tci_given imp)
139 -- instType i@(EqInst {tci_co = co}) = eitherEqInst i TyVarTy id
140 instType (EqInst {tci_left = ty1, tci_right = ty2}) = mkPredTy (EqPred ty1 ty2)
142 mkImplicTy tvs givens wanteds -- The type of an implication constraint
143 = ASSERT( all isAbstractableInst givens )
144 -- pprTrace "mkImplicTy" (ppr givens) $
145 -- See [Equational Constraints in Implication Constraints]
146 let dict_wanteds = filter (not . isEqInst) wanteds
149 mkPhiTy (map dictPred givens) $
150 if isSingleton dict_wanteds then
151 instType (head dict_wanteds)
153 mkTupleTy Boxed (length dict_wanteds) (map instType dict_wanteds)
155 dictPred (Dict {tci_pred = pred}) = pred
156 dictPred (EqInst {tci_left=ty1,tci_right=ty2}) = EqPred ty1 ty2
157 dictPred inst = pprPanic "dictPred" (ppr inst)
159 getDictClassTys (Dict {tci_pred = pred}) = getClassPredTys pred
160 getDictClassTys inst = pprPanic "getDictClassTys" (ppr inst)
162 -- fdPredsOfInst is used to get predicates that contain functional
163 -- dependencies *or* might do so. The "might do" part is because
164 -- a constraint (C a b) might have a superclass with FDs
165 -- Leaving these in is really important for the call to fdPredsOfInsts
166 -- in TcSimplify.inferLoop, because the result is fed to 'grow',
167 -- which is supposed to be conservative
168 fdPredsOfInst (Dict {tci_pred = pred}) = [pred]
169 fdPredsOfInst (Method {tci_theta = theta}) = theta
170 fdPredsOfInst (ImplicInst {tci_given = gs,
171 tci_wanted = ws}) = fdPredsOfInsts (gs ++ ws)
172 fdPredsOfInst (LitInst {}) = []
173 fdPredsOfInst (EqInst {}) = []
175 fdPredsOfInsts :: [Inst] -> [PredType]
176 fdPredsOfInsts insts = concatMap fdPredsOfInst insts
178 isInheritableInst (Dict {tci_pred = pred}) = isInheritablePred pred
179 isInheritableInst (Method {tci_theta = theta}) = all isInheritablePred theta
180 isInheritableInst other = True
183 ---------------------------------
184 -- Get the implicit parameters mentioned by these Insts
185 -- NB: the results of these functions are insensitive to zonking
187 ipNamesOfInsts :: [Inst] -> [Name]
188 ipNamesOfInst :: Inst -> [Name]
189 ipNamesOfInsts insts = [n | inst <- insts, n <- ipNamesOfInst inst]
191 ipNamesOfInst (Dict {tci_pred = IParam n _}) = [ipNameName n]
192 ipNamesOfInst (Method {tci_theta = theta}) = [ipNameName n | IParam n _ <- theta]
193 ipNamesOfInst other = []
195 ---------------------------------
196 tyVarsOfInst :: Inst -> TcTyVarSet
197 tyVarsOfInst (LitInst {tci_ty = ty}) = tyVarsOfType ty
198 tyVarsOfInst (Dict {tci_pred = pred}) = tyVarsOfPred pred
199 tyVarsOfInst (Method {tci_oid = id, tci_tys = tys}) = tyVarsOfTypes tys `unionVarSet` varTypeTyVars id
200 -- The id might have free type variables; in the case of
201 -- locally-overloaded class methods, for example
202 tyVarsOfInst (ImplicInst {tci_tyvars = tvs, tci_given = givens, tci_wanted = wanteds})
203 = (tyVarsOfInsts givens `unionVarSet` tyVarsOfInsts wanteds)
204 `minusVarSet` mkVarSet tvs
205 `unionVarSet` unionVarSets (map varTypeTyVars tvs)
206 -- Remember the free tyvars of a coercion
207 tyVarsOfInst (EqInst {tci_left = ty1, tci_right = ty2}) = tyVarsOfType ty1 `unionVarSet` tyVarsOfType ty2
209 tyVarsOfInsts insts = foldr (unionVarSet . tyVarsOfInst) emptyVarSet insts
210 tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie)
213 --------------------------
214 instToDictBind :: Inst -> LHsExpr TcId -> TcDictBinds
215 instToDictBind inst rhs
216 = unitBag (L (instSpan inst) (VarBind (instToId inst) rhs))
218 addInstToDictBind :: TcDictBinds -> Inst -> LHsExpr TcId -> TcDictBinds
219 addInstToDictBind binds inst rhs = binds `unionBags` instToDictBind inst rhs
226 isAbstractableInst :: Inst -> Bool
227 isAbstractableInst inst = isDict inst || isEqInst inst
229 isEqInst :: Inst -> Bool
230 isEqInst (EqInst {}) = True
231 isEqInst other = False
233 isDict :: Inst -> Bool
234 isDict (Dict {}) = True
237 isClassDict :: Inst -> Bool
238 isClassDict (Dict {tci_pred = pred}) = isClassPred pred
239 isClassDict other = False
241 isTyVarDict :: Inst -> Bool
242 isTyVarDict (Dict {tci_pred = pred}) = isTyVarClassPred pred
243 isTyVarDict other = False
245 isIPDict :: Inst -> Bool
246 isIPDict (Dict {tci_pred = pred}) = isIPPred pred
247 isIPDict other = False
249 isImplicInst (ImplicInst {}) = True
250 isImplicInst other = False
252 isMethod :: Inst -> Bool
253 isMethod (Method {}) = True
254 isMethod other = False
256 isMethodFor :: TcIdSet -> Inst -> Bool
257 isMethodFor ids (Method {tci_oid = id}) = id `elemVarSet` ids
258 isMethodFor ids inst = False
260 isMethodOrLit :: Inst -> Bool
261 isMethodOrLit (Method {}) = True
262 isMethodOrLit (LitInst {}) = True
263 isMethodOrLit other = False
267 %************************************************************************
269 \subsection{Building dictionaries}
271 %************************************************************************
273 -- newDictBndrs makes a dictionary at a binding site
274 -- instCall makes a dictionary at an occurrence site
275 -- and throws it into the LIE
279 newDictBndrsO :: InstOrigin -> TcThetaType -> TcM [Inst]
280 newDictBndrsO orig theta = do { loc <- getInstLoc orig
281 ; newDictBndrs loc theta }
283 newDictBndrs :: InstLoc -> TcThetaType -> TcM [Inst]
284 newDictBndrs inst_loc theta = mapM (newDictBndr inst_loc) theta
286 newDictBndr :: InstLoc -> TcPredType -> TcM Inst
287 newDictBndr inst_loc pred@(EqPred ty1 ty2)
288 = do { uniq <- newUnique
289 ; let name = mkPredName uniq inst_loc pred
290 ; return (EqInst {tci_name = name,
294 tci_co = mkGivenCo $ TyVarTy (Var.mkCoVar name (PredTy pred))})
296 newDictBndr inst_loc pred
297 = do { uniq <- newUnique
298 ; let name = mkPredName uniq inst_loc pred
299 ; return (Dict {tci_name = name, tci_pred = pred, tci_loc = inst_loc}) }
302 instCall :: InstOrigin -> [TcType] -> TcThetaType -> TcM HsWrapper
303 -- Instantiate the constraints of a call
304 -- (instCall o tys theta)
305 -- (a) Makes fresh dictionaries as necessary for the constraints (theta)
306 -- (b) Throws these dictionaries into the LIE
307 -- (c) Returns an HsWrapper ([.] tys dicts)
309 instCall orig tys theta
310 = do { loc <- getInstLoc orig
311 ; dict_app <- instCallDicts loc theta
312 ; return (dict_app <.> mkWpTyApps tys) }
315 instStupidTheta :: InstOrigin -> TcThetaType -> TcM ()
316 -- Similar to instCall, but only emit the constraints in the LIE
317 -- Used exclusively for the 'stupid theta' of a data constructor
318 instStupidTheta orig theta
319 = do { loc <- getInstLoc orig
320 ; _co <- instCallDicts loc theta -- Discard the coercion
324 instCallDicts :: InstLoc -> TcThetaType -> TcM HsWrapper
325 -- Instantiates the TcTheta, puts all constraints thereby generated
326 -- into the LIE, and returns a HsWrapper to enclose the call site.
327 -- This is the key place where equality predicates
328 -- are unleashed into the world
329 instCallDicts loc [] = return idHsWrapper
331 -- instCallDicts loc (EqPred ty1 ty2 : preds)
332 -- = do { unifyType ty1 ty2 -- For now, we insist that they unify right away
333 -- -- Later on, when we do associated types,
334 -- -- unifyType :: Type -> Type -> TcM ([Inst], Coercion)
335 -- ; (dicts, co_fn) <- instCallDicts loc preds
336 -- ; return (dicts, co_fn <.> WpTyApp ty1) }
337 -- -- We use type application to apply the function to the
338 -- -- coercion; here ty1 *is* the appropriate identity coercion
340 instCallDicts loc (EqPred ty1 ty2 : preds)
341 = do { traceTc (text "instCallDicts" <+> ppr (EqPred ty1 ty2))
342 ; coi <- boxyUnify ty1 ty2
343 -- ; coi <- unifyType ty1 ty2
344 ; let co = fromCoI coi ty1
345 ; co_fn <- instCallDicts loc preds
346 ; return (co_fn <.> WpTyApp co) }
348 instCallDicts loc (pred : preds)
349 = do { uniq <- newUnique
350 ; let name = mkPredName uniq loc pred
351 dict = Dict {tci_name = name, tci_pred = pred, tci_loc = loc}
353 ; co_fn <- instCallDicts loc preds
354 ; return (co_fn <.> WpApp (instToId dict)) }
357 cloneDict :: Inst -> TcM Inst
358 cloneDict dict@(Dict nm ty loc) = do { uniq <- newUnique
359 ; return (dict {tci_name = setNameUnique nm uniq}) }
360 cloneDict eq@(EqInst {}) = return eq
361 cloneDict other = pprPanic "cloneDict" (ppr other)
363 -- For vanilla implicit parameters, there is only one in scope
364 -- at any time, so we used to use the name of the implicit parameter itself
365 -- But with splittable implicit parameters there may be many in
366 -- scope, so we make up a new namea.
367 newIPDict :: InstOrigin -> IPName Name -> Type
368 -> TcM (IPName Id, Inst)
369 newIPDict orig ip_name ty
370 = getInstLoc orig `thenM` \ inst_loc ->
371 newUnique `thenM` \ uniq ->
373 pred = IParam ip_name ty
374 name = mkPredName uniq inst_loc pred
375 dict = Dict {tci_name = name, tci_pred = pred, tci_loc = inst_loc}
377 returnM (mapIPName (\n -> instToId dict) ip_name, dict)
382 mkPredName :: Unique -> InstLoc -> PredType -> Name
383 mkPredName uniq loc pred_ty
384 = mkInternalName uniq occ (instLocSpan loc)
386 occ = case pred_ty of
387 ClassP cls _ -> mkDictOcc (getOccName cls)
388 IParam ip _ -> getOccName (ipNameName ip)
389 EqPred ty _ -> mkEqPredCoOcc baseOcc
391 -- we use the outermost tycon of the lhs, if there is one, to
392 -- improve readability of Core code
393 baseOcc = case splitTyConApp_maybe ty of
394 Nothing -> mkOccName tcName "$"
395 Just (tc, _) -> getOccName tc
398 %************************************************************************
400 \subsection{Building methods (calls of overloaded functions)}
402 %************************************************************************
406 newMethodFromName :: InstOrigin -> BoxyRhoType -> Name -> TcM TcId
407 newMethodFromName origin ty name
408 = tcLookupId name `thenM` \ id ->
409 -- Use tcLookupId not tcLookupGlobalId; the method is almost
410 -- always a class op, but with -fno-implicit-prelude GHC is
411 -- meant to find whatever thing is in scope, and that may
412 -- be an ordinary function.
413 getInstLoc origin `thenM` \ loc ->
414 tcInstClassOp loc id [ty] `thenM` \ inst ->
415 extendLIE inst `thenM_`
416 returnM (instToId inst)
418 newMethodWithGivenTy orig id tys
419 = getInstLoc orig `thenM` \ loc ->
420 newMethod loc id tys `thenM` \ inst ->
421 extendLIE inst `thenM_`
422 returnM (instToId inst)
424 --------------------------------------------
425 -- tcInstClassOp, and newMethod do *not* drop the
426 -- Inst into the LIE; they just returns the Inst
427 -- This is important because they are used by TcSimplify
430 -- NB: the kind of the type variable to be instantiated
431 -- might be a sub-kind of the type to which it is applied,
432 -- notably when the latter is a type variable of kind ??
433 -- Hence the call to checkKind
434 -- A worry: is this needed anywhere else?
435 tcInstClassOp :: InstLoc -> Id -> [TcType] -> TcM Inst
436 tcInstClassOp inst_loc sel_id tys
438 (tyvars, _rho) = tcSplitForAllTys (idType sel_id)
440 zipWithM_ checkKind tyvars tys `thenM_`
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
462 = newUnique `thenM` \ new_uniq ->
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 = tcMetaTy integerTyConName `thenM` \ integer_ty ->
501 getSrcSpanM `thenM` \ span ->
502 returnM (L span $ HsLit (HsInteger i integer_ty))
504 mkRatLit :: Rational -> TcM (LHsExpr TcId)
506 = tcMetaTy rationalTyConName `thenM` \ rat_ty ->
507 getSrcSpanM `thenM` \ span ->
508 returnM (L span $ HsLit (HsRat r rat_ty))
510 mkStrLit :: FastString -> TcM (LHsExpr TcId)
512 = --tcMetaTy stringTyConName `thenM` \ string_ty ->
513 getSrcSpanM `thenM` \ span ->
514 returnM (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})
533 = zonkTcPredType pred `thenM` \ new_pred ->
534 returnM (dict {tci_pred = new_pred})
536 zonkInst meth@(Method {tci_oid = id, tci_tys = tys, tci_theta = theta})
537 = zonkId id `thenM` \ new_id ->
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 zonkTcTypes tys `thenM` \ new_tys ->
543 zonkTcThetaType theta `thenM` \ new_theta ->
544 returnM (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})
548 = zonkTcType ty `thenM` \ new_ty ->
549 returnM (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 = mappM 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 (instName inst) <+> dcolon
606 <+> (braces (ppr (instType inst) <> implicWantedEqs) $$
607 ifPprDebug implic_stuff)
609 (implic_stuff, implicWantedEqs)
610 | isImplicInst inst = (ppr (tci_reft inst),
612 ppr (filter isEqInst (tci_wanted inst)))
613 | otherwise = (empty, empty)
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 = returnM (GenInst [] (noLoc expr))
787 = ASSERT( from_integer_name `isHsVar` fromIntegerName ) -- A LitInst invariant
788 tcLookupId fromIntegerName `thenM` \ from_integer ->
789 tcInstClassOp loc from_integer [ty] `thenM` \ method_inst ->
790 mkIntegerLit i `thenM` \ integer_lit ->
791 returnM (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 = returnM (GenInst [] (noLoc expr))
800 = ASSERT( from_rat_name `isHsVar` fromRationalName ) -- A LitInst invariant
801 tcLookupId fromRationalName `thenM` \ from_rational ->
802 tcInstClassOp loc from_rational [ty] `thenM` \ method_inst ->
803 mkRatLit f `thenM` \ rat_lit ->
804 returnM (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 = returnM (GenInst [] (noLoc expr))
811 = ASSERT( from_string_name `isHsVar` fromStringName ) -- A LitInst invariant
812 tcLookupId fromStringName `thenM` \ from_string ->
813 tcInstClassOp loc from_string [ty] `thenM` \ method_inst ->
814 mkStrLit s `thenM` \ string_lit ->
815 returnM (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 <- mappM inst_tv mb_inst_tys
840 (theta, _) = tcSplitPhiTy (applyTys (idType dfun_id) tys)
841 src_loc = instLocSpan loc
844 returnM (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 ; returnM (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 = newMethodFromName orig ty std_nm `thenM` \ id ->
945 returnM (std_nm, HsVar id)
947 tcSyntaxName orig ty (std_nm, user_nm_expr)
948 = tcLookupId std_nm `thenM` \ std_id ->
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) $
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
961 getSrcSpanM `thenM` \ span ->
962 tcPolyExpr (L span user_nm_expr) sigma1 `thenM` \ expr ->
963 returnM (std_nm, unLoc expr)
965 syntaxNameCtxt name orig ty tidy_env
966 = getInstLoc orig `thenM` \ inst_loc ->
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 returnM (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}