src/Pure/Isar/outer_syntax.ML

--- a/src/Pure/Isar/outer_syntax.ML	Thu Jul 05 14:13:14 2012 +0200
+++ b/src/Pure/Isar/outer_syntax.ML	Thu Jul 05 15:40:57 2012 +0200
@@ -69,7 +69,9 @@
   (case cmd name of
     SOME (Command {int_only, parse, ...}) =>
       Parse.!!! (Scan.prompt (name ^ "# ") (Parse.tags |-- parse >> pair int_only))
-  | NONE => raise Fail ("No parser for outer syntax command " ^ quote name));
+  | NONE =>
+      Scan.succeed (false, Toplevel.imperative (fn () =>
+        error ("Bad parser for outer syntax command " ^ quote name))));
 
 in