[project @ 2002-05-23 15:51:26 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcSimplify.lhs b/ghc/compiler/typecheck/TcSimplify.lhs
index c7280a3..c28105a 100644 (file)
--- a/ghc/compiler/typecheck/TcSimplify.lhs
+++ b/ghc/compiler/typecheck/TcSimplify.lhs
@@ -1609,15 +1609,25 @@ tcSimplifyTop wanted_lie
                -- Collect together all the bad guys
        bad_guys = non_stds ++ concat std_bads
     in
-       -- Disambiguate the ones that look feasible
-    mapTc disambigGroup std_oks                `thenTc` \ binds_ambig ->
 
-       -- And complain about the ones that don't
+    ifErrsTc (returnTc []) (
+       -- Don't check for ambiguous things
+       -- if there has been an error; errors often
+       -- give rise to spurious ambiguous Insts
+       
+    
+       -- And complain about the ones that don't fall under
+       -- the Haskell rules for disambiguation
        -- This group includes both non-existent instances
        --      e.g. Num (IO a) and Eq (Int -> Int)
        -- and ambiguous dictionaries
        --      e.g. Num a
-    addTopAmbigErrs bad_guys           `thenNF_Tc_`
+        addTopAmbigErrs bad_guys       `thenNF_Tc_`
+
+       -- Disambiguate the ones that look feasible
+        mapTc disambigGroup std_oks
+    )                                  `thenTc` \ binds_ambig ->
+
 
     returnTc (binds `andMonoBinds` andMonoBindList binds_ambig)
   where