-- Dictionaries
lookupInst dict@(Dict _ pred@(ClassP clas tys) loc)
- = do { dflags <- getDOpts
- ; if all tcIsTyVarTy tys &&
- not (dopt Opt_AllowUndecidableInstances dflags)
- -- Common special case; no lookup
- -- NB: tcIsTyVarTy... don't look through newtypes!
- -- Don't take this short cut if we allow undecidable instances
- -- because we might have "instance T a where ...".
- -- [That means we need -fallow-undecidable-instances in the
- -- client module, as well as the module with the instance decl.]
- then return NoInstance
-
- else do
- { pkg_ie <- loadImportedInsts clas tys
+ = do { pkg_ie <- loadImportedInsts clas tys
-- Suck in any instance decls that may be relevant
; tcg_env <- getGblEnv
+ ; dflags <- getDOpts
; case lookupInstEnv dflags (pkg_ie, tcg_inst_env tcg_env) clas tys of {
([(tenv, (_,_,dfun_id))], []) -> instantiate_dfun tenv dfun_id pred loc ;
(matches, unifs) -> do
{ traceTc (text "lookupInst fail" <+> vcat [text "dict" <+> ppr pred,
text "matches" <+> ppr matches,
text "unifs" <+> ppr unifs])
- ; return NoInstance } } } }
+ ; return NoInstance } } }
-- In the case of overlap (multiple matches) we report
-- NoInstance here. That has the effect of making the
-- context-simplifier return the dict as an irreducible one.
isIPDict, isInheritableInst, pprDFuns, pprDictsTheta
)
import TcEnv ( tcGetGlobalTyVars, tcLookupId, findGlobals )
-import InstEnv ( lookupInstEnv, classInstEnv )
+import InstEnv ( lookupInstEnv, classInstances )
import TcMType ( zonkTcTyVarsAndFV, tcInstTyVars, checkAmbiguity )
import TcType ( TcTyVar, TcTyVarSet, ThetaType, TyVarDetails(VanillaTv),
mkClassPred, isOverloadedTy, mkTyConApp,
-- NB that (?x::t1) and (?x::t2) will be held separately in avails
-- so that improve will see them separate
eqns = improve get_insts preds
- get_insts clas = classInstEnv home_ie clas ++ classInstEnv pkg_ie clas
+ get_insts clas = classInstances home_ie clas ++ classInstances pkg_ie clas
in
if null eqns then
returnM True
| not (isClassDict dict) = (overlap_doc, dict : no_inst_dicts)
| otherwise
= case lookupInstEnv dflags inst_envs clas tys of
- res@(ms, _)
- | length ms > 1 -> (mk_overlap_msg dict res $$ overlap_doc, no_inst_dicts)
- | otherwise -> (overlap_doc, dict : no_inst_dicts) -- No match
- -- NB: there can be exactly one match, in the case where we have
- -- instance C a where ...
- -- (In this case, lookupInst doesn't bother to look up,
- -- unless -fallow-undecidable-instances is set.)
- -- So we report this as "no instance" rather than "overlap"; the fix is
- -- to specify -fallow-undecidable-instances, but we leave that to the programmer!
+ -- The case of exactly one match and no unifiers means
+ -- a successful lookup. That can't happen here.
+#ifdef DEBUG
+ ([m],[]) -> pprPanic "addNoInstanceErrs" (ppr dict)
+#endif
+ ([], _) -> (overlap_doc, dict : no_inst_dicts) -- No match
+ res -> (mk_overlap_msg dict res $$ overlap_doc, no_inst_dicts)
where
(clas,tys) = getDictClassTys dict
in
+
+ -- Now generate a good message for the no-instance bunch
mk_probable_fix tidy_env2 mb_what no_inst_dicts `thenM` \ (tidy_env3, probable_fix) ->
let
no_inst_doc | null no_inst_dicts = empty
| otherwise = sep [ptext SLIT("Could not deduce") <+> pprDictsTheta no_inst_dicts,
nest 2 $ ptext SLIT("from the context") <+> pprDictsTheta tidy_givens]
in
+ -- And emit both the non-instance and overlap messages
addErrTcM (tidy_env3, no_inst_doc $$ overlap_doc)
-
where
mk_overlap_msg dict (matches, unifiers)
= vcat [ addInstLoc [dict] ((ptext SLIT("Overlapping instances for")
<+> pprPred (dictPred dict))),
sep [ptext SLIT("Matching instances") <> colon,
nest 2 (pprDFuns (dfuns ++ unifiers))],
- if null unifiers
- then empty
- else parens (ptext SLIT("The choice depends on the instantiation of") <+>
- quotes (pprWithCommas ppr (varSetElems (tyVarsOfInst dict))))]
+ ASSERT( not (null matches) )
+ if not (isSingleton matches)
+ then -- Two or more matches
+ empty
+ else -- One match, plus some unifiers
+ ASSERT( not (null unifiers) )
+ parens (vcat [ptext SLIT("The choice depends on the instantiation of") <+>
+ quotes (pprWithCommas ppr (varSetElems (tyVarsOfInst dict))),
+ ptext SLIT("Use -fallow-incoherent-instances to use the first choice above")])]
where
dfuns = [df | (_, (_,_,df)) <- matches]
emptyInstEnv, extendInstEnv,
lookupInstEnv,
- classInstEnv, simpleDFunClassTyCon, checkFunDeps
+ classInstances, simpleDFunClassTyCon, checkFunDeps
) where
#include "HsVersions.h"
import Class ( Class, classTvsFds )
-import Var ( Id )
+import Var ( Id, isTcTyVar )
import VarSet
import VarEnv
-import TcType ( Type, tcTyConAppTyCon,
- tcSplitDFunTy, tyVarsOfTypes,
+import TcType ( Type, tcTyConAppTyCon, tcIsTyVarTy,
+ tcSplitDFunTy, tyVarsOfTypes, isExistentialTyVar,
matchTys, unifyTyListsX
)
import FunDeps ( checkClsFD )
import TyCon ( TyCon )
import Outputable
-import UniqFM ( UniqFM, lookupWithDefaultUFM, emptyUFM, addToUFM_C )
+import UniqFM ( UniqFM, lookupUFM, emptyUFM, addToUFM_C )
import Id ( idType )
import CmdLineOpts
import Util ( notNull )
\begin{code}
type DFunId = Id
type InstEnv = UniqFM ClsInstEnv -- Maps Class to instances for that class
-type ClsInstEnv = [InstEnvElt] -- The instances for a particular class
+
+data ClsInstEnv
+ = ClsIE [InstEnvElt] -- The instances for a particular class, in any order
+ Bool -- True <=> there is an instance of form C a b c
+ -- If *not* then the common case of looking up
+ -- (C a b c) can fail immediately
+ -- NB: use tcIsTyVarTy: don't look through newtypes!!
+
type InstEnvElt = (TyVarSet, [Type], DFunId)
-- INVARIANTs: see notes below
emptyInstEnv :: InstEnv
emptyInstEnv = emptyUFM
-classInstEnv :: InstEnv -> Class -> ClsInstEnv
-classInstEnv env cls = lookupWithDefaultUFM env [] cls
+classInstances :: InstEnv -> Class -> [InstEnvElt]
+classInstances env cls = case lookupUFM env cls of
+ Just (ClsIE insts _) -> insts
+ Nothing -> []
extendInstEnv :: InstEnv -> DFunId -> InstEnv
extendInstEnv inst_env dfun_id
- = addToUFM_C add inst_env clas [ins_item]
+ = addToUFM_C add inst_env clas (ClsIE [ins_item] ins_tyvar)
where
- add old _ = ins_item : old
+ add (ClsIE cur_insts cur_tyvar) _ = ClsIE (ins_item : cur_insts)
+ (ins_tyvar || cur_tyvar)
(ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun_id)
ins_tv_set = mkVarSet ins_tvs
ins_item = (ins_tv_set, ins_tys, dfun_id)
+ ins_tyvar = all tcIsTyVarTy ins_tys
#ifdef UNUSED
pprInstEnv :: InstEnv -> SDoc
pprInstEnv env
= vcat [ brackets (pprWithCommas ppr (varSetElems tyvars)) <+>
brackets (pprWithCommas ppr tys) <+> ppr dfun
- | cls_inst_env <- eltsUFM env
+ | ClsIE cls_inst_env _ <- eltsUFM env
, (tyvars, tys, dfun) <- cls_inst_env
]
#endif
-- so don't attempt to pune the matches
| otherwise = (pruned_matches, [])
where
+ all_tvs = all tcIsTyVarTy tys
incoherent_ok = dopt Opt_AllowIncoherentInstances dflags
overlap_ok = dopt Opt_AllowOverlappingInstances dflags
- (home_matches, home_unifs) = lookup_inst_env home_ie cls tys
- (pkg_matches, pkg_unifs) = lookup_inst_env pkg_ie cls tys
+ (home_matches, home_unifs) = lookup_inst_env home_ie cls tys all_tvs
+ (pkg_matches, pkg_unifs) = lookup_inst_env pkg_ie cls tys all_tvs
all_matches = home_matches ++ pkg_matches
all_unifs | incoherent_ok = [] -- Don't worry about these if incoherent is ok!
| otherwise = home_unifs ++ pkg_unifs
lookup_inst_env :: InstEnv -- The envt
-> Class -> [Type] -- What we are looking for
+ -> Bool -- All the [Type] are tyvars
-> ([(TyVarSubstEnv, InstEnvElt)], -- Successful matches
[Id]) -- These don't match but do unify
-lookup_inst_env env key_cls key_tys
- = find (classInstEnv env key_cls) [] []
+lookup_inst_env env key_cls key_tys key_all_tvs
+ = case lookupUFM env key_cls of
+ Nothing -> ([],[]) -- No instances for this class
+ Just (ClsIE insts has_tv_insts)
+ | key_all_tvs && not has_tv_insts -> ([],[]) -- Short cut for common case
+ -- The thing we are looking up is of form (C a b c), and
+ -- the ClsIE has no instances of that form, so don't bother to search
+ | otherwise -> find insts [] []
where
- key_vars = tyVarsOfTypes key_tys
+ key_vars = filterVarSet not_existential (tyVarsOfTypes key_tys)
+ not_existential tv = not (isTcTyVar tv && isExistentialTyVar tv)
+ -- The key_tys can contain skolem constants, and we can guarantee that those
+ -- are never going to be instantiated to anything, so we should not involve
+ -- them in the unification test. Example:
+ -- class Foo a where { op :: a -> Int }
+ -- instance Foo a => Foo [a] -- NB overlap
+ -- instance Foo [Int] -- NB overlap
+ -- data T = forall a. Foo a => MkT a
+ -- f :: T -> Int
+ -- f (MkT x) = op [x,x]
+ -- The op [x,x] means we need (Foo [a]). Without the filterVarSet we'd
+ -- complain, saying that the choice of instance depended on the instantiation
+ -- of 'a'; but of course it isn't *going* to be instantiated.
find [] ms us = (ms, us)
find (item@(tpl_tyvars, tpl, dfun_id) : rest) ms us
where
(ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun)
ins_tv_set = mkVarSet ins_tvs
- cls_inst_env = classInstEnv home_ie clas ++ classInstEnv pkg_ie clas
+ cls_inst_env = classInstances home_ie clas ++ classInstances pkg_ie clas
bad_fundeps = badFunDeps cls_inst_env clas ins_tv_set ins_tys
-badFunDeps :: ClsInstEnv -> Class
+badFunDeps :: [InstEnvElt] -> Class
-> TyVarSet -> [Type] -- Proposed new instance type
-> [DFunId]
badFunDeps cls_inst_env clas ins_tv_set ins_tys
projects / ghc-hetmet.git / commitdiff