src/HOLCF/Tools/domain/domain_syntax.ML

     fun arg1 n (con,_,args) = foldr cabs (expvar n) (argvars n args);
     fun when1 n m = if n = m then arg1 n else K (Constant "UU");
 
     fun app_var x = mk_appl (Constant "_var") [x, Variable "rhs"];
     fun app_pat x = mk_appl (Constant "_pat") [x];
-    fun args_list [] = Constant "Unity"
+    fun args_list [] = Constant "_noargs"
     |   args_list xs = foldr1 (app "_args") xs;
   in
     val case_trans = ParsePrintRule
         (app "_case_syntax" (Variable "x", foldr1 (app "_case2") (mapn case1 1 cons')),
          capp (Library.foldl capp (Constant (dnam^"_when"), mapn arg1 1 cons'), Variable "x"));