src/Pure/Isar/proof_history.ML

 sig
   type T
   val position: T -> int
   val init: int option -> Proof.state -> T
   val is_initial: T -> bool
+  val map_current: (Proof.state -> Proof.state) -> T -> T
   val current: T -> Proof.state
   val previous: T -> Proof.state option
   val clear: int -> T -> T
   val undo: T -> T
   val redo: T -> T

 
 type node =
   Proof.state *                 (*first result*)
   Proof.state Seq.seq;          (*alternative results*)
 
-type proof = node * node list;
+type proof = node * int;        (*proof node, proof position*)
 
 datatype T = ProofHistory of proof History.T;
 
 fun app f (ProofHistory x) = ProofHistory (f x);
 fun hist_app f = app (History.apply f);
+fun hist_map f = app (History.map_current f);
 
-fun position (ProofHistory prf) = length (snd (History.current prf));
+fun position (ProofHistory prf) = snd (History.current prf);
 
 
 (* generic history operations *)
 
-fun init lim st = ProofHistory (History.init lim ((st, Seq.empty), []));
+fun init lim st = ProofHistory (History.init lim ((st, Seq.empty), 0));
 fun is_initial (ProofHistory prf) = History.is_initial prf;
+fun map_current f = hist_map (apfst (apfst f));
 fun current (ProofHistory prf) = fst (fst (History.current prf));
 fun previous (ProofHistory prf) = Option.map (fst o fst) (History.previous prf);
 val clear = app o History.clear;
 val undo = app History.undo;
 val redo = app History.redo;
 
 
 (* backtracking *)
 
-val back = hist_app (fn ((_, stq), nodes) =>
+val back = hist_app (fn ((_, stq), position) =>
   (case Seq.pull stq of
     NONE => error "back: no alternatives"
-  | SOME result => (result, nodes)));
+  | SOME result => (result, position)));
 
 
 (* apply transformer *)
 
-fun applys f = hist_app (fn (node as (st, _), nodes) =>
+fun applys f = hist_app (fn (node as (st, _), position) =>
   (case Seq.pull (f st) of
     NONE => error "empty result sequence -- proof command failed"
-  | SOME results => (results, node :: nodes)));
+  | SOME results => (results, position + 1)));
 
 fun apply f = applys (Seq.single o f);
 
 
 end;