[project @ 2000-05-14 07:16:50 by lewie]

Wobble.  Fine tuning tcSimplifyAndCheck a bit further (wrt implicit params).
The key is that a method that doesn't constrain a local tyvar, but does has
implicit params, needs to be reduced further.

ghc/compiler/typecheck/Inst.lhs

@@ -25,7 +25,8 @@ module Inst (
 
 	lookupInst, lookupSimpleInst, LookupInstResult(..),
 
-	isDict, isClassDict, isTyVarDict, isStdClassTyVarDict, isMethodFor, notFunDep,
+	isDict, isClassDict, isMethod,
+	isTyVarDict, isStdClassTyVarDict, isMethodFor, notFunDep,
 	instBindingRequired, instCanBeGeneralised,
 
 	zonkInst, zonkInsts, zonkFunDeps, zonkTvFunDeps,
@@ -302,10 +303,14 @@ Predicates
 \begin{code}
 isDict :: Inst -> Bool
 isDict (Dict _ _ _) = True
-isDict other	      = False
+isDict other	    = False
 isClassDict :: Inst -> Bool
 isClassDict (Dict _ (Class _ _) _) = True
-isClassDict other	      = False
+isClassDict other		   = False
+
+isMethod :: Inst -> Bool
+isMethod (Method _ _ _ _ _ _) = True
+isMethod other		      = False
 
 isMethodFor :: TcIdSet -> Inst -> Bool
 isMethodFor ids (Method uniq id tys _ _ loc) 
@@ -574,10 +579,10 @@ pprInst (Dict u pred loc) = pprPred pred <+> show_uniq u
 
 pprInst m@(Method u id tys theta tau loc)
   = hsep [ppr id, ptext SLIT("at"), 
-	  brackets (interppSP tys),
+	  brackets (interppSP tys) {- ,
 	  ppr theta, ppr tau,
 	  show_uniq u,
-	  ppr (instToId m)]
+	  ppr (instToId m) -}]
 
 pprInst (FunDep clas fds loc)
   = hsep [ppr clas, ppr fds]

ghc/compiler/typecheck/TcSimplify.lhs

@@ -132,7 +132,7 @@ import TcHsSyn		( TcExpr, TcId,
 import TcMonad
 import Inst		( lookupInst, lookupSimpleInst, LookupInstResult(..),
 			  tyVarsOfInst, tyVarsOfInsts,
-			  isDict, isClassDict, isStdClassTyVarDict,
+			  isDict, isClassDict, isMethod, isStdClassTyVarDict,
 			  isMethodFor, notFunDep,
 			  instToId, instBindingRequired, instCanBeGeneralised,
 			  newDictFromOld,
@@ -299,6 +299,7 @@ tcSimplifyAndCheck str local_tvs given_lie wanted_lie
     try_me inst 
       -- Does not constrain a local tyvar
       | isEmptyVarSet (tyVarsOfInst inst `intersectVarSet` local_tvs)
+        && (not (isMethod inst) || null (getIPs inst))
       = Free
 
       -- When checking against a given signature we always reduce