import Var ( TyVar )
import Class ( Class, FunDep, classTvsFds )
-import Type ( Type, PredType(..), predTyUnique, tyVarsOfTypes, tyVarsOfPred )
+import Type ( Type, ThetaType, PredType(..), predTyUnique, tyVarsOfTypes, tyVarsOfPred )
import Subst ( mkSubst, emptyInScopeSet, substTy )
-import Unify ( unifyTyListsX )
+import Unify ( unifyTyListsX, unifyExtendTysX )
import Outputable ( Outputable, SDoc, interppSP, ptext, empty, hsep, punctuate, comma )
import VarSet
import VarEnv
import List ( tails )
+import Maybes ( maybeToBool )
import ListSetOps ( equivClassesByUniq )
\end{code}
-- In our example, tv_fds will be [ ({x,y}, {z}), ({x,p},{q}) ]
-- Meaning "knowing x,y fixes z, knowing x,p fixes q"
tv_fds = [ (tyVarsOfTypes xs, tyVarsOfTypes ys)
- | Class cls tys <- preds, -- Ignore implicit params
+ | ClassP cls tys <- preds, -- Ignore implicit params
let (cls_tvs, cls_fds) = classTvsFds cls,
fd <- cls_fds,
let (xs,ys) = instFD fd cls_tvs tys
\begin{code}
----------
-type Equation = (Type,Type) -- These two types should be equal
- -- INVARIANT: they aren't already equal
+type Equation = (TyVarSet, Type,Type) -- These two types should be equal, for some
+ -- substitution of the tyvars in the tyvar set
+ -- For example, ({a,b}, (a,Int,b), (Int,z,Bool))
+ -- We unify z with Int, but since a and b are quantified we do nothing to them
+ -- We usually act on an equation by instantiating the quantified type varaibles
+ -- to fresh type variables, and then calling the standard unifier.
+ --
+ -- INVARIANT: they aren't already equal
+
+
----------
improve :: InstEnv a -- Gives instances for given class
checkGroup inst_env (IParam _ ty : ips)
= -- For implicit parameters, all the types must match
- [(ty, ty') | IParam _ ty' <- ips, ty /= ty']
+ [(emptyVarSet, ty, ty') | IParam _ ty' <- ips, ty /= ty']
-checkGroup inst_env clss@(Class cls tys : _)
+checkGroup inst_env clss@(ClassP cls tys : _)
= -- For classes life is more complicated
-- Suppose the class is like
-- classs C as | (l1 -> r1), (l2 -> r2), ... where ...
- -- Then FOR EACH PAIR (Class c tys1, Class c tys2) in the list clss
+ -- Then FOR EACH PAIR (ClassP c tys1, ClassP c tys2) in the list clss
-- we check whether
-- U l1[tys1/as] = U l2[tys2/as]
-- (where U is a unifier)
-- NOTE that we iterate over the fds first; they are typically
-- empty, which aborts the rest of the loop.
- pairwise_eqns :: [(Type,Type)]
+ pairwise_eqns :: [Equation]
pairwise_eqns -- This group comes from pairwise comparison
= [ eqn | fd <- cls_fds,
- Class _ tys1 : rest <- tails clss,
- Class _ tys2 <- rest,
+ ClassP _ tys1 : rest <- tails clss,
+ ClassP _ tys2 <- rest,
eqn <- checkClsFD emptyVarSet fd cls_tvs tys1 tys2
]
- instance_eqns :: [(Type,Type)]
+ instance_eqns :: [Equation]
instance_eqns -- This group comes from comparing with instance decls
= [ eqn | fd <- cls_fds,
(qtvs, tys1, _) <- cls_inst_env,
- Class _ tys2 <- clss,
+ ClassP _ tys2 <- clss,
eqn <- checkClsFD qtvs fd cls_tvs tys1 tys2
]
----------
-checkClsFD :: TyVarSet
+checkClsFD :: TyVarSet -- The quantified type variables, which
+ -- can be instantiated to make the types match
-> FunDep TyVar -> [TyVar] -- One functional dependency from the class
-> [Type] -> [Type]
-> [Equation]
-- unifyTyListsX will only bind variables in qtvs, so it's OK!
= case unifyTyListsX qtvs ls1 ls2 of
Nothing -> []
- Just unif -> [(sr1, sr2) | (r1,r2) <- rs1 `zip` rs2,
- let sr1 = substTy full_unif r1,
- let sr2 = substTy full_unif r2,
- sr1 /= sr2]
+ Just unif -> [ (qtvs', substTy full_unif r1, substTy full_unif r2)
+ | (r1,r2) <- rs1 `zip` rs2,
+ not (maybeToBool (unifyExtendTysX qtvs unif r1 r2))]
where
full_unif = mkSubst emptyInScopeSet unif
-- No for-alls in sight; hmm
+
+ qtvs' = filterVarSet (\v -> not (v `elemSubstEnv` unif)) qtvs
+ -- qtvs' are the quantified type variables
+ -- that have not been substituted out
where
(ls1, rs1) = instFD fd clas_tvs tys1
(ls2, rs2) = instFD fd clas_tvs tys2
\end{code}
\begin{code}
-checkInstFDs :: Class -> [Type] -> Bool
+checkInstFDs :: ThetaType -> Class -> [Type] -> Bool
-- Check that functional dependencies are obeyed in an instance decl
-- For example, if we have
--- class C a b | a -> b
+-- class theta => C a b | a -> b
-- instance C t1 t2
--- Then we require fv(t2) `subset` fv(t1)
+-- Then we require fv(t2) `subset` oclose(fv(t1), theta)
-checkInstFDs clas inst_taus
+checkInstFDs theta clas inst_taus
= all fundep_ok fds
where
(tyvars, fds) = classTvsFds clas
- fundep_ok fd = tyVarsOfTypes rs `subVarSet` tyVarsOfTypes ls
+ fundep_ok fd = tyVarsOfTypes rs `subVarSet` oclose theta (tyVarsOfTypes ls)
where
(ls,rs) = instFD fd tyvars inst_taus
\end{code}
projects / ghc-hetmet.git / blobdiff