InstEnv, emptyInstEnv, extendInstEnv,
extendInstEnvList, lookupInstEnv, instEnvElts,
- classInstances,
+ classInstances, instanceBindFun,
instanceCantMatch, roughMatchTcs
) where
import Name
import TcType
import TyCon
-import TcGadt
import Unify
import Outputable
import BasicTypes
import UniqFM
import Id
-import SrcLoc
+import FastString
import Data.Maybe ( isJust, isNothing )
\end{code}
-- are ok; hence the assert
ispec { is_dfun = dfun, is_tvs = mkVarSet tvs, is_tys = tys }
where
- (tvs, _, _, tys) = tcSplitDFunTy (idType dfun)
+ (tvs, _, tys) = tcSplitDFunTy (idType dfun)
instanceRoughTcs :: Instance -> [Maybe Name]
instanceRoughTcs = is_tcs
pprInstance :: Instance -> SDoc
-- Prints the Instance as an instance declaration
-pprInstance ispec@(Instance { is_flag = flag })
+pprInstance ispec
= hang (pprInstanceHdr ispec)
- 2 (ptext SLIT("--") <+> (pprDefnLoc (getSrcSpan ispec)))
+ 2 (ptext (sLit "--") <+> pprNameLoc (getName ispec))
-- * pprInstanceHdr is used in VStudio to populate the ClassView tree
pprInstanceHdr :: Instance -> SDoc
-- Prints the Instance as an instance declaration
pprInstanceHdr ispec@(Instance { is_flag = flag })
- = ptext SLIT("instance") <+> ppr flag
- <+> sep [pprThetaArrow theta, pprClassPred clas tys]
+ = ptext (sLit "instance") <+> ppr flag
+ <+> sep [pprThetaArrow theta, ppr res_ty]
where
- (_, theta, clas, tys) = instanceHead ispec
+ (_, theta, res_ty) = tcSplitSigmaTy (idType (is_dfun ispec))
-- Print without the for-all, which the programmer doesn't write
pprInstances :: [Instance] -> SDoc
pprInstances ispecs = vcat (map pprInstance ispecs)
-instanceHead :: Instance -> ([TyVar], [PredType], Class, [Type])
-instanceHead ispec = tcSplitDFunTy (idType (is_dfun ispec))
+instanceHead :: Instance -> ([TyVar], ThetaType, Class, [Type])
+instanceHead ispec
+ = (tvs, theta, cls, tys)
+ where
+ (tvs, theta, tau) = tcSplitSigmaTy (idType (is_dfun ispec))
+ (cls, tys) = tcSplitDFunHead tau
mkLocalInstance :: DFunId -> OverlapFlag -> Instance
-- Used for local instances, where we can safely pull on the DFunId
is_tvs = mkVarSet tvs, is_tys = tys,
is_cls = className cls, is_tcs = roughMatchTcs tys }
where
- (tvs, _, cls, tys) = tcSplitDFunTy (idType dfun)
+ (tvs, cls, tys) = tcSplitDFunTy (idType dfun)
mkImportedInstance :: Name -> [Maybe Name]
-> DFunId -> OverlapFlag -> Instance
is_tvs = mkVarSet tvs, is_tys = tys,
is_cls = cls, is_tcs = mb_tcs }
where
- (tvs, _, _, tys) = tcSplitDFunTy (idType dfun)
+ (tvs, _, tys) = tcSplitDFunTy (idType dfun)
roughMatchTcs :: [Type] -> [Maybe Name]
roughMatchTcs tys = map rough tys
-- possibly be instantiated to actual, nor vice versa;
-- False is non-committal
instanceCantMatch (Just t : ts) (Just a : as) = t/=a || instanceCantMatch ts as
-instanceCantMatch ts as = False -- Safe
+instanceCantMatch _ _ = False -- Safe
\end{code}
add (ClsIE cur_insts cur_tyvar) _ = ClsIE (ins_item : cur_insts)
(ins_tyvar || cur_tyvar)
ins_tyvar = not (any isJust mb_tcs)
-\end{code}
+\end{code}
%************************************************************************
%* *
-\subsection{Looking up an instance}
+ Looking up an instance
%* *
%************************************************************************
)
-- Unification will break badly if the variables overlap
-- They shouldn't because we allocate separate uniques for them
- case tcUnifyTys bind_fn tpl_tys tys of
+ case tcUnifyTys instanceBindFun tpl_tys tys of
Just _ -> find ms (item:us) rest
- Nothing -> find ms us rest
+ Nothing -> find ms us rest
---------------
-bind_fn tv | isTcTyVar tv && isExistentialTyVar tv = Skolem
- | otherwise = BindMe
- -- 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.
- --
- -- We do this only for pattern-bound skolems. For example we reject
- -- g :: forall a => [a] -> Int
- -- g x = op x
- -- on the grounds that the correct instance depends on the instantiation of 'a'
-
---------------
insert_overlapping :: InstMatch -> [InstMatch] -> [InstMatch]
-- Add a new solution, knocking out strictly less specific ones
where
overlap_ok = case is_flag instB of
NoOverlap -> False
- other -> True
+ _ -> True
\end{code}
+
+%************************************************************************
+%* *
+ Binding decisions
+%* *
+%************************************************************************
+
+\begin{code}
+instanceBindFun :: TyVar -> BindFlag
+instanceBindFun tv | isTcTyVar tv && isExistentialTyVar tv = Skolem
+ | otherwise = BindMe
+ -- Note [Binding when looking up instances]
+\end{code}
+
+Note [Binding when looking up instances]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When looking up in the instance environment, or family-instance environment,
+we are careful about multiple matches, as described above in
+Note [Overlapping instances]
+
+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.
+
+We do this only for pattern-bound skolems. For example we reject
+ g :: forall a => [a] -> Int
+ g x = op x
+on the grounds that the correct instance depends on the instantiation of 'a'
projects / ghc-hetmet.git / blobdiff