--- a/src/Pure/Isar/isar_cmd.ML Wed May 26 22:43:27 1999 +0200
+++ b/src/Pure/Isar/isar_cmd.ML Wed May 26 22:43:50 1999 +0200
@@ -11,6 +11,7 @@
val exit: Toplevel.transition -> Toplevel.transition
val restart: Toplevel.transition -> Toplevel.transition
val quit: Toplevel.transition -> Toplevel.transition
+ val cannot_undo: string -> Toplevel.transition -> Toplevel.transition
val clear_undo: Toplevel.transition -> Toplevel.transition
val undo: Toplevel.transition -> Toplevel.transition
val redo: Toplevel.transition -> Toplevel.transition
@@ -56,6 +57,8 @@
(* history commands *)
+fun cannot_undo txt = Toplevel.imperative (fn () => error ("Cannot undo " ^ quote txt));
+
val clear_undo = Toplevel.history History.clear o Toplevel.proof ProofHistory.clear;
val redo = Toplevel.history History.redo o Toplevel.proof ProofHistory.redo;