src/Pure/Syntax/scan.ML

       ([], _) => (finite' stopper scan (state, xs), src)
     | (xs', src') => drain def_prmpt get stopper scan ((state, xs @ xs'), src'));
 
 fun source' def_prmpt get unget stopper scanner opt_recover (state, src) =
   let
-    val drain_with = drain def_prmpt get stopper;
+    fun drain_with scan = drain def_prmpt get stopper scan;
 
     fun drain_loop recover inp =
       drain_with (catch scanner) inp handle FAIL msg =>
         (warning (if_none msg "Syntax error."); warning "Trying to recover ...";
           drain_loop recover (apfst snd (drain_with recover inp)));