X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=e26c97d2c6ce9189e075f340d76c8e125e85938a;hp=b973ec4a2cef1d64a0070b1bc34120d4aebd10fb;hb=00b6d2567426ec52a113b1d3687e1d61368cafda;hpb=481b014b46dd53ef5d1c5e679e1d9f08207af96e

diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs
index b973ec4..e26c97d 100644
--- a/compiler/typecheck/TcDeriv.lhs
+++ b/compiler/typecheck/TcDeriv.lhs
@@ -479,7 +479,8 @@ mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args
 	; let ordinary_constraints
 	        = [ mkClassPred cls [arg_ty] 
 	          | data_con <- tyConDataCons rep_tc,
-	            arg_ty   <- dataConInstOrigArgTys data_con rep_tc_args,
+	            arg_ty   <- ASSERT( isVanillaDataCon data_con )
+				dataConInstOrigArgTys data_con rep_tc_args,
 	            not (isUnLiftedType arg_ty) ] -- No constraints for unlifted types?
 
 	      tiresome_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args