Fix Trac #2334: validity checking for type families

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

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index 203ffe4..a2d8242 100644 (file)
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -187,6 +187,9 @@ tcInstDecls1 tycl_decls inst_decls deriv_decls
                 -- decl, so it needs to know about all the instances possible
                 -- NB: class instance declarations can contain derivings as
                 --     part of associated data type declarations
+        failIfErrsM            -- If the addInsts stuff gave any errors, don't
+                               -- try the deriving stuff, becuase that may give
+                               -- more errors still
        ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls inst_decls
                                                       deriv_decls
        ; addInsts deriv_inst_info   $ do {