\begin{code}
module FunDeps (
Equation, pprEquation,
- oclose, grow, improveOne,
+ oclose, improveOne,
checkInstCoverage, checkFunDeps,
pprFundeps
) where
]
\end{code}
-Note [Growing the tau-tvs using constraints]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-(grow preds tvs) is the result of extend the set of tyvars tvs
- using all conceivable links from pred
-
-E.g. tvs = {a}, preds = {H [a] b, K (b,Int) c, Eq e}
-Then grow precs tvs = {a,b,c}
-
-All the type variables from an implicit parameter are added, whether or
-not they are mentioned in tvs; see Note [Implicit parameters and ambiguity]
-in TcSimplify.
-
-See also Note [Ambiguity] in TcSimplify
-
-\begin{code}
-grow :: [PredType] -> TyVarSet -> TyVarSet
-grow preds fixed_tvs
- | null preds = fixed_tvs
- | otherwise = loop real_fixed_tvs
- where
- -- Add the implicit parameters;
- -- see Note [Implicit parameters and ambiguity] in TcSimplify
- real_fixed_tvs = foldr unionVarSet fixed_tvs ip_tvs
-
- loop fixed_tvs
- | new_fixed_tvs `subVarSet` fixed_tvs = fixed_tvs
- | otherwise = loop new_fixed_tvs
- where
- new_fixed_tvs = foldl extend fixed_tvs non_ip_tvs
-
- extend fixed_tvs pred_tvs
- | fixed_tvs `intersectsVarSet` pred_tvs = fixed_tvs `unionVarSet` pred_tvs
- | otherwise = fixed_tvs
-
- (ip_tvs, non_ip_tvs) = partitionWith get_ip preds
- get_ip (IParam _ ty) = Left (tyVarsOfType ty)
- get_ip other = Right (tyVarsOfPred other)
-\end{code}
%************************************************************************
%* *
pprEquation :: Equation -> SDoc
pprEquation (qtvs, pairs)
= vcat [ptext (sLit "forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)),
- nest 2 (vcat [ ppr t1 <+> ptext (sLit ":=:") <+> ppr t2 | (t1,t2) <- pairs])]
+ nest 2 (vcat [ ppr t1 <+> ptext (sLit "~") <+> ppr t2 | (t1,t2) <- pairs])]
\end{code}
Given a bunch of predicates that must hold, such as
, not (instanceCantMatch inst_tcs trimmed_tcs)
, eqn <- checkClsFD qtvs fd cls_tvs tys_inst tys
, let p_inst = (mkClassPred cls tys_inst,
- ptext (sLit "arising from the instance declaration at")
- <+> ppr (getSrcLoc ispec))
+ sep [ ptext (sLit "arising from the dependency") <+> quotes (pprFunDep fd)
+ , ptext (sLit "in the instance declaration at")
+ <+> ppr (getSrcLoc ispec)])
]
improveOne _ _ _
-- tys2 = [Maybe t1, t2]
--
-- We can instantiate x to t1, and then we want to force
--- (Tree x) [t1/x] :=: t2
+-- (Tree x) [t1/x] ~ t2
--
-- This function is also used when matching two Insts (rather than an Inst
-- against an instance decl. In that case, qtvs is empty, and we are doing
trimRoughMatchTcs :: [TyVar] -> FunDep TyVar -> [Maybe Name] -> [Maybe Name]
-- Computing rough_tcs for a particular fundep
--- class C a b c | a -> b where ...
+-- class C a b c | a -> b where ...
-- For each instance .... => C ta tb tc
--- we want to match only on the types ta, tc; so our
+-- we want to match only on the type ta; so our
-- rough-match thing must similarly be filtered.
--- Hence, we Nothing-ise the tb type right here
-trimRoughMatchTcs clas_tvs (_,rtvs) mb_tcs
+-- Hence, we Nothing-ise the tb and tc types right here
+trimRoughMatchTcs clas_tvs (ltvs, _) mb_tcs
= zipWith select clas_tvs mb_tcs
where
- select clas_tv mb_tc | clas_tv `elem` rtvs = Nothing
- | otherwise = mb_tc
+ select clas_tv mb_tc | clas_tv `elem` ltvs = mb_tc
+ | otherwise = Nothing
\end{code}