Implementation of a new backtracking system, that allow to go back

anywhere in a script (provided no suspend/resume is used):

* the command "Backtrack n m p" (vernac_bactrack) performs the
  following operation:

** do abort p times,
** do undo on the current proof (after the aborts) in order to reach a
   stack depth of m (see vernac_undo_todepth)
** resets the global state to state labelled with n.

* The coq prompt in emacs mode has more informations, it contains:

** the usual coq prompt plus:
** the state number (global state label)
** the depth of the current proof stack
** the names of all pending proofs, in *unspecified* order, separated by '|'

 Example:

     state                        proof stack
      num                           depth
       __                              _
 aux < 12 |aux|SmallStepAntiReflexive| 4 < ù
 ^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^     ^
 usual           pending proofs           usual
                                          special char


git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@6947 85f007b7-540e-0410-9357-904b9bb8a0f7

2 files changed, 29 insertions, 0 deletions

diff --git a/lib/edit.ml b/lib/edit.ml
index 096fa5dc1..06a55d171 100644
--- a/lib/edit.ml
+++ b/lib/edit.ml
@@ -84,6 +84,28 @@ let undo e n =
 	  errorlabstrm "Edit.undo" (str"Undo stack exhausted");
         repeat n Bstack.pop bs
 
+(* Return the depth of the focused proof of [e] stack, this is used to
+   put informations in coq prompt (in emacs mode). *)
+let depth e =
+  match e.focus with
+    | None -> invalid_arg "Edit.depth"
+    | Some d ->
+	let (bs,_) = Hashtbl.find e.buf d in
+	Bstack.depth bs
+
+(* Undo focused proof of [e] to reach depth [n] *)
+let undo_todepth e n =
+  match e.focus with
+    | None -> 
+	if n <> 0 
+	then errorlabstrm "Edit.undo_todepth" (str"No proof in progress")
+	else () (* if there is no proof in progress, then n must be zero *)
+    | Some d ->
+	let (bs,_) = Hashtbl.find e.buf d in
+	if Bstack.depth bs < n then
+	  errorlabstrm "Edit.undo_todepth" (str"Undo stack would be exhausted");
+        repeat (Bstack.depth bs - n) Bstack.pop bs
+
 let create e (d,b,c,udepth) =
   if Hashtbl.mem e.buf d then
     errorlabstrm "Edit.create" 
diff --git a/lib/edit.mli b/lib/edit.mli
index 0bd802fcc..d13d9c6f6 100644
--- a/lib/edit.mli
+++ b/lib/edit.mli
@@ -54,3 +54,10 @@ val delete : ('a,'b,'c) t -> 'a -> unit
 val dom : ('a,'b,'c) t -> 'a list
 
 val clear : ('a,'b,'c) t -> unit
+
+(* [depth e] Returns the depth of the focused proof stack of [e], this
+   is used to put informations in coq prompt (in emacs mode). *)
+val depth : ('a,'b,'c) t -> int
+
+(* [undo_todepth e n] Undoes focused proof of [e] to reach depth [n] *)
+val undo_todepth : ('a,'b,'c) t -> int -> unit