Comments only

[ghc-hetmet.git] / compiler / types / FunDeps.lhs

diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs
index 7f9f050..02b0a2a 100644 (file)
--- a/compiler/types/FunDeps.lhs
+++ b/compiler/types/FunDeps.lhs
@@ -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, improveOne,
+       oclose, improveOne,
        checkInstCoverage, checkFunDeps,
        pprFundeps
     ) where
@@ -132,44 +132,6 @@ oclose preds fixed_tvs
              ]
 \end{code}
 
-Note [Growing the tau-tvs using constraints]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-(grow preds tvs) is the result of extend the set of tyvars tvs
-                using all conceivable links from pred
-
-E.g. tvs = {a}, preds = {H [a] b, K (b,Int) c, Eq e}
-Then grow precs tvs = {a,b,c}
-
-All the type variables from an implicit parameter are added, whether or
-not they are mentioned in tvs; see Note [Implicit parameters and ambiguity] 
-in TcSimplify.
-
-See also Note [Ambiguity] in TcSimplify
-
-\begin{code}
-grow :: [PredType] -> TyVarSet -> TyVarSet
-grow preds fixed_tvs 
-  | null preds = fixed_tvs
-  | otherwise  = loop real_fixed_tvs
-  where
-       -- Add the implicit parameters; 
-       -- see Note [Implicit parameters and ambiguity] in TcSimplify
-    real_fixed_tvs = foldr unionVarSet fixed_tvs ip_tvs
- 
-    loop fixed_tvs
-       | new_fixed_tvs `subVarSet` fixed_tvs = fixed_tvs
-       | otherwise                           = loop new_fixed_tvs
-       where
-         new_fixed_tvs = foldl extend fixed_tvs non_ip_tvs
-
-    extend fixed_tvs pred_tvs 
-       | fixed_tvs `intersectsVarSet` pred_tvs = fixed_tvs `unionVarSet` pred_tvs
-       | otherwise                             = fixed_tvs
-
-    (ip_tvs, non_ip_tvs) = partitionWith get_ip preds
-    get_ip (IParam _ ty) = Left (tyVarsOfType ty)
-    get_ip other         = Right (tyVarsOfPred other)
-\end{code}
     
 %************************************************************************
 %*                                                                     *
@@ -203,7 +165,7 @@ type Equation = (TyVarSet, [(Type, Type)])
 pprEquation :: Equation -> SDoc
 pprEquation (qtvs, pairs) 
   = vcat [ptext (sLit "forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)),
-         nest 2 (vcat [ ppr t1 <+> ptext (sLit ":=:") <+> ppr t2 | (t1,t2) <- pairs])]
+         nest 2 (vcat [ ppr t1 <+> ptext (sLit "~") <+> ppr t2 | (t1,t2) <- pairs])]
 \end{code}
 
 Given a bunch of predicates that must hold, such as
@@ -294,8 +256,9 @@ improveOne inst_env pred@(ClassP cls tys, _) preds
        , not (instanceCantMatch inst_tcs trimmed_tcs)
        , eqn <- checkClsFD qtvs fd cls_tvs tys_inst tys
        , let p_inst = (mkClassPred cls tys_inst, 
-                       ptext (sLit "arising from the instance declaration at")
-                       <+> ppr (getSrcLoc ispec))
+                       sep [ ptext (sLit "arising from the dependency") <+> quotes (pprFunDep fd)
+                           , ptext (sLit "in the instance declaration at") 
+                                 <+> ppr (getSrcLoc ispec)])
        ]
 
 improveOne _ _ _
@@ -320,7 +283,7 @@ checkClsFD qtvs fd clas_tvs tys1 tys2
 --                 tys2 = [Maybe t1, t2]
 --
 -- We can instantiate x to t1, and then we want to force
---     (Tree x) [t1/x]  :=:   t2
+--     (Tree x) [t1/x]  ~   t2
 --
 -- This function is also used when matching two Insts (rather than an Inst
 -- against an instance decl. In that case, qtvs is empty, and we are doing