-import Inst (getDictClassTys)
-import Class (classTvsFds)
-import Type (getTyVar_maybe, tyVarsOfType)
-import Outputable (interppSP, ptext, empty, hsep, punctuate, comma)
-import UniqSet (elementOfUniqSet, addOneToUniqSet,
- uniqSetToList, unionManyUniqSets)
-import List (elemIndex)
-import Maybe (catMaybes)
-import FastString
-
-oclose fds vs =
- case oclose1 fds vs of
- (vs', False) -> vs'
- (vs', True) -> oclose fds vs'
-
-oclose1 [] vs = (vs, False)
-oclose1 (fd@(ls, rs):fds) vs =
- if osubset ls vs then
- (vs'', b1 || b2)
- else
- vs'b1
- where
- vs'b1@(vs', b1) = oclose1 fds vs
- (vs'', b2) = ounion rs vs'
-
-osubset [] vs = True
-osubset (u:us) vs = if u `elementOfUniqSet` vs then osubset us vs else False
-
-ounion [] ys = (ys, False)
-ounion (x:xs) ys =
- if x `elementOfUniqSet` ys then (ys', b) else (addOneToUniqSet ys' x, True)
- where
- (ys', b) = ounion xs ys
-
--- instantiate fundeps to type variables
-instantiateFundeps dict =
- map (\(xs, ys) -> (unionMap getTyVars xs, unionMap getTyVars ys)) fdtys
- where
- fdtys = instantiateFdTys dict
- getTyVars ty = tyVarsOfType ty
- unionMap f xs = uniqSetToList (unionManyUniqSets (map f xs))
-
--- instantiate fundeps to types
-instantiateFdTys dict = instantiateFdClassTys clas ts
- where (clas, ts) = getDictClassTys dict
-instantiateFdClassTys clas ts =
- map (lookupInstFundep tyvars ts) fundeps
- where
- (tyvars, fundeps) = classTvsFds clas
- lookupInstFundep tyvars ts (us, vs) =
- (lookupInstTys tyvars ts us, lookupInstTys tyvars ts vs)
-lookupInstTys tyvars ts = map (lookupInstTy tyvars ts)
-lookupInstTy tyvars ts u = ts !! i
- where Just i = elemIndex u tyvars
+import Name ( getSrcLoc )
+import Var ( Id, TyVar )
+import Class ( Class, FunDep, classTvsFds )
+import Unify ( tcUnifyTys, BindFlag(..) )
+import Type ( substTys, notElemTvSubst )
+import TcType ( Type, ThetaType, PredType(..), tcEqType,
+ predTyUnique, mkClassPred, tyVarsOfTypes, tyVarsOfPred )
+import VarSet
+import VarEnv
+import Outputable
+import List ( tails )
+import Maybe ( isJust )
+import ListSetOps ( equivClassesByUniq )
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Close type variables}
+%* *
+%************************************************************************
+
+(oclose preds tvs) closes the set of type variables tvs,
+wrt functional dependencies in preds. The result is a superset
+of the argument set. For example, if we have
+ class C a b | a->b where ...
+then
+ oclose [C (x,y) z, C (x,p) q] {x,y} = {x,y,z}
+because if we know x and y then that fixes z.
+
+Using oclose
+~~~~~~~~~~~~
+oclose is used
+
+a) When determining ambiguity. The type
+ forall a,b. C a b => a
+is not ambiguous (given the above class decl for C) because
+a determines b.
+
+b) When generalising a type T. Usually we take FV(T) \ FV(Env),
+but in fact we need
+ FV(T) \ (FV(Env)+)
+where the '+' is the oclosure operation. Notice that we do not
+take FV(T)+. This puzzled me for a bit. Consider
+
+ f = E
+
+and suppose e have that E :: C a b => a, and suppose that b is
+free in the environment. Then we quantify over 'a' only, giving
+the type forall a. C a b => a. Since a->b but we don't have b->a,
+we might have instance decls like
+ instance C Bool Int where ...
+ instance C Char Int where ...
+so knowing that b=Int doesn't fix 'a'; so we quantify over it.
+
+ ---------------
+ A WORRY: ToDo!
+ ---------------
+If we have class C a b => D a b where ....
+ class D a b | a -> b where ...
+and the preds are [C (x,y) z], then we want to see the fd in D,
+even though it is not explicit in C, giving [({x,y},{z})]
+
+Similarly for instance decls? E.g. Suppose we have
+ instance C a b => Eq (T a b) where ...
+and we infer a type t with constraints Eq (T a b) for a particular
+expression, and suppose that 'a' is free in the environment.
+We could generalise to
+ forall b. Eq (T a b) => t
+but if we reduced the constraint, to C a b, we'd see that 'a' determines
+b, so that a better type might be
+ t (with free constraint C a b)
+Perhaps it doesn't matter, because we'll still force b to be a
+particular type at the call sites. Generalising over too many
+variables (provided we don't shadow anything by quantifying over a
+variable that is actually free in the envt) may postpone errors; it
+won't hide them altogether.
+
+
+\begin{code}
+oclose :: [PredType] -> TyVarSet -> TyVarSet
+oclose preds fixed_tvs
+ | null tv_fds = fixed_tvs -- Fast escape hatch for common case
+ | otherwise = loop fixed_tvs
+ where
+ loop fixed_tvs
+ | new_fixed_tvs `subVarSet` fixed_tvs = fixed_tvs
+ | otherwise = loop new_fixed_tvs
+ where
+ new_fixed_tvs = foldl extend fixed_tvs tv_fds
+
+ extend fixed_tvs (ls,rs) | ls `subVarSet` fixed_tvs = fixed_tvs `unionVarSet` rs
+ | otherwise = fixed_tvs
+
+ tv_fds :: [(TyVarSet,TyVarSet)]
+ -- 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)
+ | 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
+ ]
+\end{code}
+
+\begin{code}
+grow :: [PredType] -> TyVarSet -> TyVarSet
+grow preds fixed_tvs
+ | null preds = fixed_tvs
+ | otherwise = loop fixed_tvs
+ where
+ loop fixed_tvs
+ | new_fixed_tvs `subVarSet` fixed_tvs = fixed_tvs
+ | otherwise = loop new_fixed_tvs
+ where
+ new_fixed_tvs = foldl extend fixed_tvs pred_sets
+
+ extend fixed_tvs pred_tvs
+ | fixed_tvs `intersectsVarSet` pred_tvs = fixed_tvs `unionVarSet` pred_tvs
+ | otherwise = fixed_tvs
+
+ pred_sets = [tyVarsOfPred pred | pred <- preds]
+\end{code}
+
+%************************************************************************
+%* *
+\subsection{Generate equations from functional dependencies}
+%* *
+%************************************************************************
+
+
+\begin{code}
+----------
+type Equation = (TyVarSet, [(Type, Type)])
+-- These pairs of types should be equal, for some
+-- substitution of the tyvars in the tyvar set
+-- INVARIANT: corresponding types aren't already equal
+
+-- It's important that we have a *list* of pairs of types. Consider
+-- class C a b c | a -> b c where ...
+-- instance C Int x x where ...
+-- Then, given the constraint (C Int Bool v) we should improve v to Bool,
+-- via the equation ({x}, [(Bool,x), (v,x)])
+-- This would not happen if the class had looked like
+-- class C a b c | a -> b, a -> c
+
+-- To "execute" the equation, make fresh type variable for each tyvar in the set,
+-- instantiate the two types with these fresh variables, and then unify.
+--
+-- 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.
+
+pprEquationDoc (eqn, doc) = vcat [pprEquation eqn, nest 2 doc]
+
+pprEquation (qtvs, pairs)
+ = vcat [ptext SLIT("forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)),
+ nest 2 (vcat [ ppr t1 <+> ptext SLIT(":=:") <+> ppr t2 | (t1,t2) <- pairs])]
+
+----------
+improve :: InstEnv Id -- Gives instances for given class
+ -> [(PredType,SDoc)] -- Current constraints; doc says where they come from
+ -> [(Equation,SDoc)] -- Derived equalities that must also hold
+ -- (NB the above INVARIANT for type Equation)
+ -- The SDoc explains why the equation holds (for error messages)
+
+type InstEnv a = Class -> [(TyVarSet, [Type], a)]
+-- This is a bit clumsy, because InstEnv is really
+-- defined in module InstEnv. However, we don't want
+-- to define it here because InstEnv
+-- is their home. Nor do we want to make a recursive
+-- module group (InstEnv imports stuff from FunDeps).
+\end{code}
+
+Given a bunch of predicates that must hold, such as