[project @ 2003-06-20 11:14:18 by simonpj]

[ghc-hetmet.git] / ghc / compiler / typecheck / Inst.lhs

diff --git a/ghc/compiler/typecheck/Inst.lhs b/ghc/compiler/typecheck/Inst.lhs
index dc96759..19c484f 100644 (file)
--- a/ghc/compiler/typecheck/Inst.lhs
+++ b/ghc/compiler/typecheck/Inst.lhs
@@ -56,7 +56,7 @@ import TcType ( Type, TcType, TcThetaType, TcTyVarSet,
                  isIntTy,isFloatTy, isIntegerTy, isDoubleTy,
                  tcIsTyVarTy, mkPredTy, mkTyVarTy, mkTyVarTys,
                  tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tidyPred,
-                 isClassPred, isTyVarClassPred, isLinearPred, predHasFDs,
+                 isClassPred, isTyVarClassPred, isLinearPred, 
                  getClassPredTys, getClassPredTys_maybe, mkPredName,
                  isInheritablePred, isIPPred, 
                  tidyType, tidyTypes, tidyFreeTyVars, tcSplitSigmaTy
@@ -101,11 +101,14 @@ dictPred inst               = pprPanic "dictPred" (ppr inst)
 getDictClassTys (Dict _ pred _) = getClassPredTys pred
 
 -- fdPredsOfInst is used to get predicates that contain functional 
--- dependencies; i.e. should participate in improvement
-fdPredsOfInst (Dict _ pred _) | predHasFDs pred = [pred]
-                             | otherwise       = []
-fdPredsOfInst (Method _ _ _ theta _ _) = filter predHasFDs theta
-fdPredsOfInst other                   = []
+-- dependencies *or* might do so.  The "might do" part is because
+-- a constraint (C a b) might have a superclass with FDs
+-- Leaving these in is really important for the call to fdPredsOfInsts
+-- in TcSimplify.inferLoop, because the result is fed to 'grow',
+-- which is supposed to be conservative
+fdPredsOfInst (Dict _ pred _)         = [pred]
+fdPredsOfInst (Method _ _ _ theta _ _) = theta
+fdPredsOfInst other                   = []     -- LitInsts etc
 
 fdPredsOfInsts :: [Inst] -> [PredType]
 fdPredsOfInsts insts = concatMap fdPredsOfInst insts