tcSimplifyInfer, tcSimplifyInferCheck,
tcSimplifyCheck, tcSimplifyRestricted,
tcSimplifyToDicts, tcSimplifyIPs,
+ tcSimplifySuperClasses,
tcSimplifyTop, tcSimplifyInteractive,
tcSimplifyBracket,
instToId, tyVarsOfInsts, cloneDict,
ipNamesOfInsts, ipNamesOfInst, dictPred,
instBindingRequired, fdPredsOfInst,
- newDictsFromOld, tcInstClassOp,
- getDictClassTys, isTyVarDict,
- instLoc, zonkInst, tidyInsts, tidyMoreInsts,
+ newDictsAtLoc, tcInstClassOp,
+ getDictClassTys, isTyVarDict, instLoc,
+ zonkInst, tidyInsts, tidyMoreInsts,
Inst, pprInsts, pprDictsInFull, pprInstInFull, tcGetInstEnvs,
isInheritableInst, pprDFuns, pprDictsTheta
)
import TcEnv ( tcGetGlobalTyVars, tcLookupId, findGlobals, pprBinders )
import InstEnv ( lookupInstEnv, classInstances )
import TcMType ( zonkTcTyVarsAndFV, tcInstTyVars, checkAmbiguity )
-import TcType ( TcTyVar, TcTyVarSet, ThetaType,
- mkClassPred, isOverloadedTy, mkTyConApp,
+import TcType ( TcTyVar, TcTyVarSet, ThetaType, TcPredType,
+ mkClassPred, isOverloadedTy, mkTyConApp, isSkolemTyVar,
mkTyVarTy, tcGetTyVar, isTyVarClassPred, mkTyVarTys,
- tyVarsOfPred, tcEqType, pprPred )
+ tyVarsOfPred, tcEqType, pprPred, mkPredTy )
import Id ( idType, mkUserLocal )
import Var ( TyVar )
import Name ( Name, getOccName, getSrcLoc )
try_me inst
| isFreeWhenInferring qtvs inst = Free
| isClassDict inst = DontReduceUnlessConstant -- Dicts
- | otherwise = ReduceMe -- Lits and Methods
+ | otherwise = ReduceMe NoSCs -- Lits and Methods
in
traceTc (text "infloop" <+> vcat [ppr tau_tvs', ppr wanteds', ppr preds,
ppr (grow preds tau_tvs'), ppr qtvs]) `thenM_`
-- global type variables in the environment; so you don't
-- need to worry about setting them before calling tcSimplifyCheck
tcSimplifyCheck doc qtvs givens wanted_lie
- = tcSimplCheck doc get_qtvs
- givens wanted_lie `thenM` \ (qtvs', binds) ->
- returnM binds
+ = ASSERT( all isSkolemTyVar qtvs )
+ do { (qtvs', frees, binds) <- tcSimplCheck doc get_qtvs AddSCs givens wanted_lie
+ ; extendLIEs frees
+ ; return binds }
where
--- get_qtvs = zonkTcTyVarsAndFV qtvs
- get_qtvs = return (mkVarSet qtvs)
+-- get_qtvs = zonkTcTyVarsAndFV qtvs
+ get_qtvs = return (mkVarSet qtvs) -- All skolems
-- tcSimplifyInferCheck is used when we know the constraints we are to simplify
TcDictBinds) -- Bindings
tcSimplifyInferCheck doc tau_tvs givens wanted_lie
- = tcSimplCheck doc get_qtvs givens wanted_lie
+ = do { (qtvs', frees, binds) <- tcSimplCheck doc get_qtvs AddSCs givens wanted_lie
+ ; extendLIEs frees
+ ; return (qtvs', binds) }
where
-- Figure out which type variables to quantify over
-- You might think it should just be the signature tyvars,
Here is the workhorse function for all three wrappers.
\begin{code}
-tcSimplCheck doc get_qtvs givens wanted_lie
- = check_loop givens wanted_lie `thenM` \ (qtvs, frees, binds, irreds) ->
+tcSimplCheck doc get_qtvs want_scs givens wanted_lie
+ = do { (qtvs, frees, binds, irreds) <- check_loop givens wanted_lie
- -- Complain about any irreducible ones
- mappM zonkInst given_dicts_and_ips `thenM` \ givens' ->
- groupErrs (addNoInstanceErrs (Just doc) givens') irreds `thenM_`
-
- -- Done
- extendLIEs frees `thenM_`
- returnM (qtvs, binds)
+ -- Complain about any irreducible ones
+ ; if not (null irreds)
+ then do { givens' <- mappM zonkInst given_dicts_and_ips
+ ; groupErrs (addNoInstanceErrs (Just doc) givens') irreds }
+ else return ()
+ ; returnM (qtvs, frees, binds) }
where
given_dicts_and_ips = filter (not . isMethod) givens
-- For error reporting, filter out methods, which are
-- When checking against a given signature we always reduce
-- until we find a match against something given, or can't reduce
try_me inst | isFreeWhenChecking qtvs' ip_set inst = Free
- | otherwise = ReduceMe
+ | otherwise = ReduceMe want_scs
in
reduceContext doc try_me givens' wanteds' `thenM` \ (no_improvement, frees, binds, irreds) ->
%************************************************************************
%* *
+ tcSimplifySuperClasses
+%* *
+%************************************************************************
+
+Note [SUPERCLASS-LOOP 1]
+~~~~~~~~~~~~~~~~~~~~~~~~
+We have to be very, very careful when generating superclasses, lest we
+accidentally build a loop. Here's an example:
+
+ class S a
+
+ class S a => C a where { opc :: a -> a }
+ class S b => D b where { opd :: b -> b }
+
+ instance C Int where
+ opc = opd
+
+ instance D Int where
+ opd = opc
+
+From (instance C Int) we get the constraint set {ds1:S Int, dd:D Int}
+Simplifying, we may well get:
+ $dfCInt = :C ds1 (opd dd)
+ dd = $dfDInt
+ ds1 = $p1 dd
+Notice that we spot that we can extract ds1 from dd.
+
+Alas! Alack! We can do the same for (instance D Int):
+
+ $dfDInt = :D ds2 (opc dc)
+ dc = $dfCInt
+ ds2 = $p1 dc
+
+And now we've defined the superclass in terms of itself.
+
+Solution: never generate a superclass selectors at all when
+satisfying the superclass context of an instance declaration.
+
+Two more nasty cases are in
+ tcrun021
+ tcrun033
+
+\begin{code}
+tcSimplifySuperClasses qtvs givens sc_wanteds
+ = ASSERT( all isSkolemTyVar qtvs )
+ do { (_, frees, binds1) <- tcSimplCheck doc get_qtvs NoSCs givens sc_wanteds
+ ; binds2 <- tc_simplify_top doc False NoSCs frees
+ ; return (binds1 `unionBags` binds2) }
+ where
+ get_qtvs = return (mkVarSet qtvs)
+ doc = ptext SLIT("instance declaration superclass context")
+\end{code}
+
+
+%************************************************************************
+%* *
\subsection{tcSimplifyRestricted}
%* *
%************************************************************************
is_nested_group = isNotTopLevel top_lvl
try_me inst | isFreeWrtTyVars qtvs inst,
(is_nested_group || isDict inst) = Free
- | otherwise = ReduceMe
+ | otherwise = ReduceMe AddSCs
in
reduceContextWithoutImprovement
doc try_me wanteds' `thenM` \ (frees, binds, irreds) ->
forall dIntegralInt.
fromIntegral Int Int dIntegralInt (scsel dIntegralInt) = id Int
-because the scsel will mess up matching. Instead we want
+because the scsel will mess up RULE matching. Instead we want
forall dIntegralInt, dNumInt.
fromIntegral Int Int dIntegralInt dNumInt = id Int
-- Reduce methods and lits only; stop as soon as we get a dictionary
try_me inst | isDict inst = KeepDictWithoutSCs -- See notes above re "WithoutSCs"
- | otherwise = ReduceMe
+ | otherwise = ReduceMe NoSCs
\end{code}
-- Simplify any methods that mention the implicit parameter
try_me inst | isFreeWrtIPs ip_set inst = Free
- | otherwise = ReduceMe
+ | otherwise = ReduceMe NoSCs
simpl_loop givens wanteds
= mappM zonkInst givens `thenM` \ givens' ->
overloaded_set = mkVarSet overloaded_ids -- There can occasionally be a lot of them
-- so it's worth building a set, so that
-- lookup (in isMethodFor) is faster
- try_me inst | isMethod inst = ReduceMe
+ try_me inst | isMethod inst = ReduceMe NoSCs
| otherwise = Free
\end{code}
\begin{code}
data WhatToDo
- = ReduceMe -- Try to reduce this
+ = ReduceMe WantSCs -- Try to reduce this
-- If there's no instance, behave exactly like
-- DontReduce: add the inst to
-- the irreductible ones, but don't
| Free -- Return as free
reduceMe :: Inst -> WhatToDo
-reduceMe inst = ReduceMe
+reduceMe inst = ReduceMe AddSCs
data WantSCs = NoSCs | AddSCs -- Tells whether we should add the superclasses
-- of a predicate when adding it to the avails
-- First, see if the inst can be reduced to a constant in one step
try_simple addFree
- ; ReduceMe -> -- It should be reduced
+ ; ReduceMe want_scs -> -- It should be reduced
lookupInst wanted `thenM` \ lookup_result ->
case lookup_result of
GenInst wanteds' rhs -> addIrred NoSCs avails wanted `thenM` \ avails1 ->
reduceList stack try_me wanteds' avails1 `thenM` \ avails2 ->
- addWanted avails2 wanted rhs wanteds'
+ addWanted want_scs avails2 wanted rhs wanteds'
-- Experiment with temporarily doing addIrred *before* the reduceList,
-- which has the effect of adding the thing we are trying
-- to prove to the database before trying to prove the things it
-- the examples in [SUPERCLASS-LOOP]
-- So we do an addIrred before, and then overwrite it afterwards with addWanted
- SimpleInst rhs -> addWanted avails wanted rhs []
+ SimpleInst rhs -> addWanted want_scs avails wanted rhs []
NoInstance -> -- No such instance!
-- Add it and its superclasses
- addIrred AddSCs avails wanted
+ addIrred want_scs avails wanted
}
where
try_simple do_this_otherwise
= lookupInst wanted `thenM` \ lookup_result ->
case lookup_result of
- SimpleInst rhs -> addWanted avails wanted rhs []
+ SimpleInst rhs -> addWanted AddSCs avails wanted rhs []
other -> do_this_otherwise avails wanted
\end{code}
--
addFree avails free = returnM (addToFM avails free IsFree)
-addWanted :: Avails -> Inst -> LHsExpr TcId -> [Inst] -> TcM Avails
-addWanted avails wanted rhs_expr wanteds
- = addAvailAndSCs avails wanted avail
+addWanted :: WantSCs -> Avails -> Inst -> LHsExpr TcId -> [Inst] -> TcM Avails
+addWanted want_scs avails wanted rhs_expr wanteds
+ = addAvailAndSCs want_scs avails wanted avail
where
avail | instBindingRequired wanted = Rhs rhs_expr wanteds
| otherwise = ASSERT( null wanteds ) NoRhs
addGiven :: Avails -> Inst -> TcM Avails
-addGiven avails given = addAvailAndSCs avails given (Given (instToId given) False)
+addGiven avails given = addAvailAndSCs AddSCs avails given (Given (instToId given) False)
+ -- Always add superclasses for 'givens'
+ --
-- No ASSERT( not (given `elemFM` avails) ) because in an instance
-- decl for Ord t we can add both Ord t and Eq t as 'givens',
-- so the assert isn't true
addIrred :: WantSCs -> Avails -> Inst -> TcM Avails
-addIrred NoSCs avails irred = returnM (addToFM avails irred Irred)
-addIrred AddSCs avails irred = ASSERT2( not (irred `elemFM` avails), ppr irred $$ ppr avails )
- addAvailAndSCs avails irred Irred
-
-addAvailAndSCs :: Avails -> Inst -> Avail -> TcM Avails
-addAvailAndSCs avails inst avail
- | not (isClassDict inst) = returnM avails1
- | otherwise = traceTc (text "addAvailAndSCs" <+> vcat [ppr inst, ppr deps]) `thenM_`
- addSCs is_loop avails1 inst
+addIrred want_scs avails irred = ASSERT2( not (irred `elemFM` avails), ppr irred $$ ppr avails )
+ addAvailAndSCs want_scs avails irred Irred
+
+addAvailAndSCs :: WantSCs -> Avails -> Inst -> Avail -> TcM Avails
+addAvailAndSCs want_scs avails inst avail
+ | not (isClassDict inst) = return avails_with_inst
+ | NoSCs <- want_scs = return avails_with_inst
+ | otherwise = do { traceTc (text "addAvailAndSCs" <+> vcat [ppr inst, ppr deps])
+ ; addSCs is_loop avails_with_inst inst }
where
- avails1 = addToFM avails inst avail
- is_loop inst = any (`tcEqType` idType (instToId inst)) dep_tys
+ avails_with_inst = addToFM avails inst avail
+
+ is_loop pred = any (`tcEqType` mkPredTy pred) dep_tys
-- Note: this compares by *type*, not by Unique
deps = findAllDeps (unitVarSet (instToId inst)) avail
dep_tys = map idType (varSetElems deps)
so_far' = extendVarSet so_far kid_id -- Add the new kid to so_far
kid_id = instToId kid
-addSCs :: (Inst -> Bool) -> Avails -> Inst -> TcM Avails
+addSCs :: (TcPredType -> Bool) -> Avails -> Inst -> TcM Avails
-- Add all the superclasses of the Inst to Avails
-- The first param says "dont do this because the original thing
-- depends on this one, so you'd build a loop"
-- Invariant: the Inst is already in Avails.
addSCs is_loop avails dict
- = newDictsFromOld dict sc_theta' `thenM` \ sc_dicts ->
- foldlM add_sc avails (zipEqual "add_scs" sc_dicts sc_sels)
+ = do { sc_dicts <- newDictsAtLoc (instLoc dict) sc_theta'
+ ; foldlM add_sc avails (zipEqual "add_scs" sc_dicts sc_sels) }
where
(clas, tys) = getDictClassTys dict
(tyvars, sc_theta, sc_sels, _) = classBigSig clas
sc_theta' = substTheta (zipTopTvSubst tyvars tys) sc_theta
- add_sc avails (sc_dict, sc_sel) -- Add it, and its superclasses
- | add_me sc_dict = addSCs is_loop avails' sc_dict
- | otherwise = returnM avails
+ add_sc avails (sc_dict, sc_sel)
+ | is_loop (dictPred sc_dict) = return avails -- See Note [SUPERCLASS-LOOP 2]
+ | is_given sc_dict = return avails
+ | otherwise = addSCs is_loop avails' sc_dict
where
sc_sel_rhs = mkHsDictApp (mkHsTyApp (L (instSpan dict) (HsVar sc_sel)) tys) [instToId dict]
avails' = addToFM avails sc_dict (Rhs sc_sel_rhs [dict])
- add_me :: Inst -> Bool
- add_me sc_dict
- | is_loop sc_dict = False -- See Note [SUPERCLASS-LOOP]
- | otherwise = case lookupFM avails sc_dict of
- Just (Given _ _) -> False -- Given is cheaper than superclass selection
- other -> True
+ is_given :: Inst -> Bool
+ is_given sc_dict = case lookupFM avails sc_dict of
+ Just (Given _ _) -> True -- Given is cheaper than superclass selection
+ other -> False
\end{code}
-Note [SUPERCLASS-LOOP]: Checking for loops
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We have to be careful here. If we are *given* d1:Ord a,
+Note [SUPERCLASS-LOOP 2]
+~~~~~~~~~~~~~~~~~~~~~~~~
+But the above isn't enough. Suppose we are *given* d1:Ord a,
and want to deduce (d2:C [a]) where
class Ord a => C a where
\begin{code}
tcSimplifyTop, tcSimplifyInteractive :: [Inst] -> TcM TcDictBinds
-tcSimplifyTop wanteds = tc_simplify_top False {- Not interactive loop -} wanteds
-tcSimplifyInteractive wanteds = tc_simplify_top True {- Interactive loop -} wanteds
+tcSimplifyTop wanteds
+ = tc_simplify_top doc False {- Not interactive loop -} AddSCs wanteds
+ where
+ doc = text "tcSimplifyTop"
+tcSimplifyInteractive wanteds
+ = tc_simplify_top doc True {- Interactive loop -} AddSCs wanteds
+ where
+ doc = text "tcSimplifyTop"
-- The TcLclEnv should be valid here, solely to improve
-- error message generation for the monomorphism restriction
-tc_simplify_top is_interactive wanteds
- = getLclEnv `thenM` \ lcl_env ->
- traceTc (text "tcSimplifyTop" <+> ppr (lclEnvElts lcl_env)) `thenM_`
- simpleReduceLoop (text "tcSimplTop") reduceMe wanteds `thenM` \ (frees, binds, irreds) ->
- ASSERT( null frees )
+tc_simplify_top doc is_interactive want_scs wanteds
+ = do { lcl_env <- getLclEnv
+ ; traceTc (text "tcSimplifyTop" <+> ppr (lclEnvElts lcl_env))
- let
+ ; let try_me inst = ReduceMe want_scs
+ ; (frees, binds, irreds) <- simpleReduceLoop doc try_me wanteds
+
+ ; let
-- All the non-std ones are definite errors
- (stds, non_stds) = partition isStdClassTyVarDict irreds
-
- -- Group by type variable
- std_groups = equivClasses cmp_by_tyvar stds
-
- -- Pick the ones which its worth trying to disambiguate
- -- namely, the onese whose type variable isn't bound
- -- up with one of the non-standard classes
- (std_oks, std_bads) = partition worth_a_try std_groups
- worth_a_try group@(d:_) = not (non_std_tyvars `intersectsVarSet` tyVarsOfInst d)
- non_std_tyvars = unionVarSets (map tyVarsOfInst non_stds)
-
- -- Collect together all the bad guys
- bad_guys = non_stds ++ concat std_bads
- (non_ips, bad_ips) = partition isClassDict bad_guys
- (ambigs, no_insts) = partition isTyVarDict non_ips
- -- If the dict has no type constructors involved, it must be ambiguous,
- -- except I suppose that another error with fundeps maybe should have
- -- constrained those type variables
- in
+ (stds, non_stds) = partition isStdClassTyVarDict irreds
+
+ -- Group by type variable
+ std_groups = equivClasses cmp_by_tyvar stds
+
+ -- Pick the ones which its worth trying to disambiguate
+ -- namely, the onese whose type variable isn't bound
+ -- up with one of the non-standard classes
+ (std_oks, std_bads) = partition worth_a_try std_groups
+ worth_a_try group@(d:_) = not (non_std_tyvars `intersectsVarSet` tyVarsOfInst d)
+ non_std_tyvars = unionVarSets (map tyVarsOfInst non_stds)
+
+ -- Collect together all the bad guys
+ bad_guys = non_stds ++ concat std_bads
+ (non_ips, bad_ips) = partition isClassDict bad_guys
+ (ambigs, no_insts) = partition isTyVarDict non_ips
+ -- If the dict has no type constructors involved, it must be ambiguous,
+ -- except I suppose that another error with fundeps maybe should have
+ -- constrained those type variables
-- Report definite errors
- groupErrs (addNoInstanceErrs Nothing []) no_insts `thenM_`
- strangeTopIPErrs bad_ips `thenM_`
+ ; ASSERT( null frees )
+ groupErrs (addNoInstanceErrs Nothing []) no_insts
+ ; strangeTopIPErrs bad_ips
-- Deal with ambiguity errors, but only if
-- if there has not been an error so far:
-- dealing with the (Num a) context arising from f's definition;
-- we try to unify a with Int (to default it), but find that it's
-- already been unified with the rigid variable from g's type sig
- ifErrsM (returnM []) (
-
- -- Complain about the ones that don't fall under
- -- the Haskell rules for disambiguation
- -- This group includes both non-existent instances
- -- e.g. Num (IO a) and Eq (Int -> Int)
- -- and ambiguous dictionaries
- -- e.g. Num a
- addTopAmbigErrs ambigs `thenM_`
+ ; binds_ambig <- ifErrsM (returnM []) $
+ do { -- Complain about the ones that don't fall under
+ -- the Haskell rules for disambiguation
+ -- This group includes both non-existent instances
+ -- e.g. Num (IO a) and Eq (Int -> Int)
+ -- and ambiguous dictionaries
+ -- e.g. Num a
+ addTopAmbigErrs ambigs
- -- Disambiguate the ones that look feasible
- mappM (disambigGroup is_interactive) std_oks
- ) `thenM` \ binds_ambig ->
+ -- Disambiguate the ones that look feasible
+ ; mappM (disambigGroup is_interactive) std_oks }
- returnM (binds `unionBags` unionManyBags binds_ambig)
+ ; return (binds `unionBags` unionManyBags binds_ambig) }
----------------------------------
d1 `cmp_by_tyvar` d2 = get_tv d1 `compare` get_tv d2
unifyTauTy default_ty (mkTyVarTy tyvar) `thenM_`
-- and reduce the context, for real this time
simpleReduceLoop (text "disambig" <+> ppr dicts)
- reduceMe dicts `thenM` \ (frees, binds, ambigs) ->
+ reduceMe dicts `thenM` \ (frees, binds, ambigs) ->
WARN( not (null frees && null ambigs), ppr frees $$ ppr ambigs )
warnDefault dicts default_ty `thenM_`
returnM binds
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