internal override void Defined(CodeGenContext context)
 {
     CILLabel endLabel = context.NewLabel();
 
     context.ldloc(0);
     context.call(Runtime.Frame.get_Tilde);
     context.dup();
     context.brfalse(endLabel);
     context.ldc_i4(nth);
     context.callvirt(Runtime.Match.defined_nth);
     context.CodeLabel(endLabel);
 }