... ... @@ -10,7 +10,7 @@ It's better to read it as: "if we know these, then we're going to know these" \begin{code} module FunDeps ( Equation, pprEquation, oclose, grow, improve, improveOne, oclose, grow, improveOne, checkInstCoverage, checkFunDeps, pprFundeps ) where ... ... @@ -27,9 +27,6 @@ import VarSet import VarEnv import Outputable import Util import ListSetOps import Data.List ( tails ) import Data.Maybe ( isJust ) \end{code} ... ... @@ -170,7 +167,6 @@ grow preds fixed_tvs \begin{code} ---------- type Equation = (TyVarSet, [(Type, Type)]) -- These pairs of types should be equal, for some -- substitution of the tyvars in the tyvar set ... ... @@ -195,16 +191,6 @@ type Equation = (TyVarSet, [(Type, Type)]) pprEquation (qtvs, pairs) = vcat [ptext SLIT("forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)), nest 2 (vcat [ ppr t1 <+> ptext SLIT(":=:") <+> ppr t2 | (t1,t2) <- pairs])] ---------- type Pred_Loc = (PredType, SDoc) -- SDoc says where the Pred comes from improve :: (Class -> [Instance]) -- Gives instances for given class -> [Pred_Loc] -- Current constraints; -> [(Equation,Pred_Loc,Pred_Loc)] -- Derived equalities that must also hold -- (NB the above INVARIANT for type Equation) -- The Pred_Locs explain which two predicates were -- combined (for error messages) \end{code} Given a bunch of predicates that must hold, such as ... ... @@ -237,20 +223,15 @@ NOTA BENE: \begin{code} improve inst_env preds = [ eqn | group <- equivClassesByUniq (predTyUnique . fst) (filterEqPreds preds), eqn <- checkGroup inst_env group ] where filterEqPreds = filter (not . isEqPred . fst) -- Equality predicates don't have uniques -- In any case, improvement *generates*, rather than -- *consumes*, equality constraints improveOne :: (Class -> [Instance]) -> Pred_Loc -> [Pred_Loc] -> [(Equation,Pred_Loc,Pred_Loc)] type Pred_Loc = (PredType, SDoc) -- SDoc says where the Pred comes from improveOne :: (Class -> [Instance]) -- Gives instances for given class -> Pred_Loc -- Do improvement triggered by this -> [Pred_Loc] -- Current constraints -> [(Equation,Pred_Loc,Pred_Loc)] -- Derived equalities that must also hold -- (NB the above INVARIANT for type Equation) -- The Pred_Locs explain which two predicates were -- combined (for error messages) -- Just do improvement triggered by a single, distinguised predicate improveOne inst_env pred@(IParam ip ty, _) preds ... ... @@ -303,72 +284,7 @@ improveOne inst_env pred@(ClassP cls tys, _) preds improveOne inst_env eq_pred preds = [] ---------- checkGroup :: (Class -> [Instance]) -> [Pred_Loc] -> [(Equation, Pred_Loc, Pred_Loc)] -- The preds are all for the same class or implicit param checkGroup inst_env (p1@(IParam _ ty, _) : ips) = -- For implicit parameters, all the types must match [ ((emptyVarSet, [(ty,ty')]), p1, p2) | p2@(IParam _ ty', _) <- ips, not (ty tcEqType ty')] checkGroup inst_env clss@((ClassP cls _, _) : _) = -- For classes life is more complicated -- Suppose the class is like -- classs C as | (l1 -> r1), (l2 -> r2), ... where ... -- 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) -- -- If so, we return the pair -- U r1[tys1/as] = U l2[tys2/as] -- -- We need to do something very similar comparing each predicate -- with relevant instance decls instance_eqns ++ pairwise_eqns -- NB: we put the instance equations first. This biases the -- order so that we first improve individual constraints against the -- instances (which are perhaps in a library and less likely to be -- wrong; and THEN perform the pairwise checks. -- The other way round, it's possible for the pairwise check to succeed -- and cause a subsequent, misleading failure of one of the pair with an -- instance declaration. See tcfail143.hs for an exmample where (cls_tvs, cls_fds) = classTvsFds cls instances = inst_env cls -- NOTE that we iterate over the fds first; they are typically -- empty, which aborts the rest of the loop. pairwise_eqns :: [(Equation,Pred_Loc,Pred_Loc)] pairwise_eqns -- This group comes from pairwise comparison = [ (eqn, p1, p2) | fd <- cls_fds, p1@(ClassP _ tys1, _) : rest <- tails clss, p2@(ClassP _ tys2, _) <- rest, eqn <- checkClsFD emptyVarSet fd cls_tvs tys1 tys2 ] instance_eqns :: [(Equation,Pred_Loc,Pred_Loc)] instance_eqns -- This group comes from comparing with instance decls = [ (eqn, p1, p2) | fd <- cls_fds, -- Iterate through the fundeps first, -- because there often are none! p2@(ClassP _ tys2, _) <- clss, let rough_tcs2 = trimRoughMatchTcs cls_tvs fd (roughMatchTcs tys2), ispec@(Instance { is_tvs = qtvs, is_tys = tys1, is_tcs = mb_tcs1 }) <- instances, not (instanceCantMatch mb_tcs1 rough_tcs2), eqn <- checkClsFD qtvs fd cls_tvs tys1 tys2, let p1 = (mkClassPred cls tys1, ptext SLIT("arising from the instance declaration at") <+> ppr (getSrcLoc ispec)) ] ---------- checkClsFD :: TyVarSet -- Quantified type variables; see note below -> FunDep TyVar -> [TyVar] -- One functional dependency from the class -> [Type] -> [Type] ... ...