Fix recursive superclasses (again). Fixes Trac #4809.

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

diff --git a/compiler/typecheck/TcErrors.lhs b/compiler/typecheck/TcErrors.lhs
index f324e40..c040473 100644 (file)
--- a/compiler/typecheck/TcErrors.lhs
+++ b/compiler/typecheck/TcErrors.lhs
@@ -343,11 +343,9 @@ getUserGivens (CEC {cec_encl = ctxt})
   where 
     givens = foldl (\gs ic -> ic_given ic ++ gs) [] ctxt
     user_givens | opt_PprStyle_Debug = givens
-                | otherwise          = filterOut isSelfDict givens
-       -- In user mode, don't show the "self-dict" given
-       -- which is only added to do co-inductive solving
-       -- Rather an awkward hack, but there we are
-       -- This is the only use of isSelfDict, so it's not in an inner loop
+                | otherwise          = filterOut isSilentEvVar givens
+       -- In user mode, don't show the "silent" givens, used for
+       -- the "self" dictionary and silent superclass arguments for dfuns
 \end{code}
 
 
@@ -437,14 +435,15 @@ reportTyVarEqErr ctxt tv1 ty2
                                -- place the equality arose to the implication site
     do { (env1, env_sigs) <- findGlobals ctxt (unitVarSet tv1)
        ; let msg = misMatchMsg ty1 ty2
-             esc_doc | isSingleton esc_skols 
-                     = ptext (sLit "because this skolem type variable would escape:")
-                     | otherwise
-                     = ptext (sLit "because these skolem type variables would escape:")
-             extra1 = vcat [ nest 2 $ esc_doc <+> pprQuotedList esc_skols
+             esc_doc = sep [ ptext (sLit "because type variable") <> plural esc_skols
+                             <+> pprQuotedList esc_skols
+                           , ptext (sLit "would escape") <+>
+                             if isSingleton esc_skols then ptext (sLit "its scope")
+                                                      else ptext (sLit "their scope") ]
+             extra1 = vcat [ nest 2 $ esc_doc
                            , sep [ (if isSingleton esc_skols 
-                                      then ptext (sLit "This skolem is")
-                                      else ptext (sLit "These skolems are"))
+                                    then ptext (sLit "This (rigid, skolem) type variable is")
+                                    else ptext (sLit "These (rigid, skolem) type variables are"))
                                    <+> ptext (sLit "bound by")
                                  , nest 2 $ pprSkolInfo (ctLocOrigin implic_loc) ] ]
        ; addErrTcM (env1, msg $$ extra1 $$ mkEnvSigMsg (ppr tv1) env_sigs) }
@@ -594,10 +593,13 @@ reportDictErrs ctxt wanteds orig
                           <+> ptext (sLit "to the context of")
                   , nest 2 $ pprErrCtxtLoc ctxt ]
 
-       fixes2 | null instance_dicts = []
-              | otherwise           = [sep [ptext (sLit "add an instance declaration for"),
-                                       pprTheta instance_dicts]]
-       instance_dicts = filterOut isTyVarClassPred wanteds
+        fixes2 = case instance_dicts of
+                   []  -> []
+                   [_] -> [sep [ptext (sLit "add an instance declaration for"),
+                                pprTheta instance_dicts]]
+                   _   -> [sep [ptext (sLit "add instance declarations for"),
+                                pprTheta instance_dicts]]
+        instance_dicts = filterOut isTyVarClassPred wanteds
                -- Insts for which it is worth suggesting an adding an 
                -- instance declaration.  Exclude tyvar dicts.