Doing the smart canonicalization only if we are not simplifying a Rule LHS.

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

diff --git a/compiler/typecheck/TcCanonical.lhs b/compiler/typecheck/TcCanonical.lhs
index b9edd5f..7fdb63e 100644 (file)
--- a/compiler/typecheck/TcCanonical.lhs
+++ b/compiler/typecheck/TcCanonical.lhs
@@ -247,8 +247,11 @@ canClass fl v cn tys
                             else setDictBind v' (EvCast v (mkSymCoercion dict_co))
                           ; return v' }
 
-       -- Add the superclasses of this one here, See Note [Adding superclasses]
-       ; sc_cts <- newSCWorkFromFlavored v_new fl cn xis
+       -- Add the superclasses of this one here, See Note [Adding superclasses]. 
+       -- But only if we are not simplifying the LHS of a rule. 
+       ; sctx <- getTcSContext
+       ; sc_cts <- if simplEqsOnly sctx then return emptyCCan 
+                   else newSCWorkFromFlavored v_new fl cn xis
 
        ; return (sc_cts `andCCan` ccs `extendCCans` CDictCan { cc_id     = v_new
                                                              , cc_flavor = fl