(*  Title:      Pure/Isar/toplevel.ML

     ID:         $Id$

     Author:     Markus Wenzel, TU Muenchen

 Isabelle/Isar toplevel transactions.

 *)

 signature TOPLEVEL =

 sig

   exception UNDEF

   type generic_theory

   type node

   val theory_node: node -> generic_theory option

   val proof_node: node -> ProofNode.T option

   val cases_node: (generic_theory -> 'a) -> (Proof.state -> 'a) -> node -> 'a

   val presentation_context: node option -> xstring option -> Proof.context

   type state

   val toplevel: state

   val is_toplevel: state -> bool

   val is_theory: state -> bool

   val is_proof: state -> bool

   val level: state -> int

   val previous_node_of: state -> node option

   val node_of: state -> node

   val node_case: (generic_theory -> 'a) -> (Proof.state -> 'a) -> state -> 'a

   val context_of: state -> Proof.context

   val generic_theory_of: state -> generic_theory

   val theory_of: state -> theory

   val proof_of: state -> Proof.state

   val proof_position_of: state -> int

   val enter_proof_body: state -> Proof.state

   val print_state_context: state -> unit

   val print_state: bool -> state -> unit

   val quiet: bool ref

   val debug: bool ref

   val interact: bool ref

   val timing: bool ref

   val profiling: int ref

   val skip_proofs: bool ref

   exception TERMINATE

   exception TOPLEVEL_ERROR

   exception CONTEXT of Proof.context * exn

   val exn_message: exn -> string

   val program: (unit -> 'a) -> 'a

   type transition

   val empty: transition

   val init_of: transition -> string option

   val name_of: transition -> string

   val str_of: transition -> string

   val name: string -> transition -> transition

   val position: Position.T -> transition -> transition

   val interactive: bool -> transition -> transition

   val print: transition -> transition

   val no_timing: transition -> transition

   val init_theory: string -> (bool -> theory) -> (theory -> unit) -> transition -> transition

   val exit: transition -> transition

   val keep: (state -> unit) -> transition -> transition

   val keep': (bool -> state -> unit) -> transition -> transition

   val imperative: (unit -> unit) -> transition -> transition

   val theory: (theory -> theory) -> transition -> transition

   val generic_theory: (generic_theory -> generic_theory) -> transition -> transition

   val theory': (bool -> theory -> theory) -> transition -> transition

   val begin_local_theory: bool -> (theory -> local_theory) -> transition -> transition

   val end_local_theory: transition -> transition

   val local_theory: xstring option -> (local_theory -> local_theory) -> transition -> transition

   val present_local_theory: xstring option -> (bool -> node -> unit) -> transition -> transition

   val local_theory_to_proof': xstring option -> (bool -> local_theory -> Proof.state) ->

     transition -> transition

   val local_theory_to_proof: xstring option -> (local_theory -> Proof.state) ->

     transition -> transition

   val theory_to_proof: (theory -> Proof.state) -> transition -> transition

   val end_proof: (bool -> Proof.state -> Proof.context) -> transition -> transition

   val forget_proof: transition -> transition

   val present_proof: (bool -> node -> unit) -> transition -> transition

   val proofs': (bool -> Proof.state -> Proof.state Seq.seq) -> transition -> transition

   val proof': (bool -> Proof.state -> Proof.state) -> transition -> transition

   val proofs: (Proof.state -> Proof.state Seq.seq) -> transition -> transition

   val proof: (Proof.state -> Proof.state) -> transition -> transition

   val actual_proof: (ProofNode.T -> ProofNode.T) -> transition -> transition

   val skip_proof: (int -> int) -> transition -> transition

   val skip_proof_to_theory: (int -> bool) -> transition -> transition

   val get_id: transition -> string option

   val put_id: string -> transition -> transition

   val unknown_theory: transition -> transition

   val unknown_proof: transition -> transition

   val unknown_context: transition -> transition

   val status: transition -> Markup.T -> unit

   val error_msg: transition -> exn * string -> unit

   val transition: bool -> transition -> state -> (state * (exn * string) option) option

   val commit_exit: transition

   val excursion: transition list -> unit

   val present_excursion: (transition * (state -> state -> 'a -> 'a)) list -> 'a -> 'a

 end;

 structure Toplevel: TOPLEVEL =

 struct

 (** toplevel state **)

 exception UNDEF;

 (* local theory wrappers *)

 type generic_theory = Context.generic;    (*theory or local_theory*)

 val loc_init = TheoryTarget.context;

 val loc_exit = ProofContext.theory_of o LocalTheory.exit;

 fun loc_begin loc (Context.Theory thy) = loc_init (the_default "-" loc) thy

   | loc_begin NONE (Context.Proof lthy) = lthy

   | loc_begin (SOME loc) (Context.Proof lthy) = loc_init loc (loc_exit lthy);

 fun loc_finish _ (Context.Theory _) = Context.Theory o loc_exit

   | loc_finish NONE (Context.Proof _) = Context.Proof o LocalTheory.restore

   | loc_finish (SOME _) (Context.Proof lthy) = fn lthy' =>

       Context.Proof (LocalTheory.reinit (LocalTheory.raw_theory (K (loc_exit lthy')) lthy));

 (* datatype node *)

 datatype node =

   Theory of generic_theory * Proof.context option

     (*theory with presentation context*) |

   Proof of ProofNode.T * ((Proof.context -> generic_theory) * generic_theory)

     (*proof node, finish, original theory*) |

   SkipProof of int * (generic_theory * generic_theory);

     (*proof depth, resulting theory, original theory*)

 val the_global_theory = fn Theory (Context.Theory thy, _) => thy | _ => raise UNDEF;

 val theory_node = fn Theory (gthy, _) => SOME gthy | _ => NONE;

 val proof_node = fn Proof (prf, _) => SOME prf | _ => NONE;

 fun cases_node f _ (Theory (gthy, _)) = f gthy

   | cases_node _ g (Proof (prf, _)) = g (ProofNode.current prf)

   | cases_node f _ (SkipProof (_, (gthy, _))) = f gthy;

 fun presentation_context (SOME (Theory (_, SOME ctxt))) NONE = ctxt

   | presentation_context (SOME node) NONE = cases_node Context.proof_of Proof.context_of node

   | presentation_context (SOME node) (SOME loc) =

       loc_init loc (cases_node Context.theory_of Proof.theory_of node)

   | presentation_context NONE _ = raise UNDEF;

 fun reset_presentation (Theory (gthy, _)) = Theory (gthy, NONE)

   | reset_presentation node = node;

 (* datatype state *)

 type node_info = node * (theory -> unit);  (*node with exit operation*)

 datatype state = State of node_info option * node_info option;  (*current, previous*)

 val toplevel = State (NONE, NONE);

 fun is_toplevel (State (NONE, _)) = true

   | is_toplevel _ = false;

 fun level (State (NONE, _)) = 0

   | level (State (SOME (Theory _, _), _)) = 0

   | level (State (SOME (Proof (prf, _), _), _)) = Proof.level (ProofNode.current prf)

   | level (State (SOME (SkipProof (d, _), _), _)) = d + 1;   (*different notion of proof depth!*)

 fun str_of_state (State (NONE, _)) = "at top level"

   | str_of_state (State (SOME (Theory (Context.Theory _, _), _), _)) = "in theory mode"

   | str_of_state (State (SOME (Theory (Context.Proof _, _), _), _)) = "in local theory mode"

   | str_of_state (State (SOME (Proof _, _), _)) = "in proof mode"

   | str_of_state (State (SOME (SkipProof _, _), _)) = "in skipped proof mode";

 (* current node *)

 fun previous_node_of (State (_, prev)) = Option.map #1 prev;

 fun node_of (State (NONE, _)) = raise UNDEF

   | node_of (State (SOME (node, _), _)) = node;

 fun is_theory state = not (is_toplevel state) andalso is_some (theory_node (node_of state));

 fun is_proof state = not (is_toplevel state) andalso is_some (proof_node (node_of state));

 fun node_case f g state = cases_node f g (node_of state);

 val context_of = node_case Context.proof_of Proof.context_of;

 val generic_theory_of = node_case I (Context.Proof o Proof.context_of);

 val theory_of = node_case Context.theory_of Proof.theory_of;

 val proof_of = node_case (fn _ => raise UNDEF) I;

 fun proof_position_of state =

   (case node_of state of

     Proof (prf, _) => ProofNode.position prf

   | _ => raise UNDEF);

 val enter_proof_body = node_case (Proof.init o Context.proof_of) Proof.enter_forward;

 (* print state *)

 val pretty_context = LocalTheory.pretty o Context.cases (TheoryTarget.init NONE) I;

 fun print_state_context state =

   (case try node_of state of

     NONE => []

   | SOME (Theory (gthy, _)) => pretty_context gthy

   | SOME (Proof (_, (_, gthy))) => pretty_context gthy

   | SOME (SkipProof (_, (gthy, _))) => pretty_context gthy)

   |> Pretty.chunks |> Pretty.writeln;

 fun print_state prf_only state =

   (case try node_of state of

     NONE => []

   | SOME (Theory (gthy, _)) => if prf_only then [] else pretty_context gthy

   | SOME (Proof (prf, _)) =>

       Proof.pretty_state (ProofNode.position prf) (ProofNode.current prf)

   | SOME (SkipProof (d, _)) => [Pretty.str ("skipped proof: depth " ^ string_of_int d)])

   |> Pretty.markup_chunks Markup.state |> Pretty.writeln;

 (** toplevel transitions **)

 val quiet = ref false;

 val debug = Output.debugging;

 val interact = ref false;

 val timing = Output.timing;

 val profiling = ref 0;

 val skip_proofs = ref false;

 exception TERMINATE;

 exception EXCURSION_FAIL of exn * string;

 exception FAILURE of state * exn;

 exception TOPLEVEL_ERROR;

 (* print exceptions *)

 exception CONTEXT of Proof.context * exn;

 fun exn_context NONE exn = exn

   | exn_context (SOME ctxt) exn = CONTEXT (ctxt, exn);

 local

 fun if_context NONE _ _ = []

   | if_context (SOME ctxt) f xs = map (f ctxt) xs;

 fun raised name [] = "exception " ^ name ^ " raised"

   | raised name [msg] = "exception " ^ name ^ " raised: " ^ msg

   | raised name msgs = cat_lines (("exception " ^ name ^ " raised:") :: msgs);

 in

 fun exn_message e =

   let

     val detailed = ! debug;

     fun exn_msg _ (CONTEXT (ctxt, exn)) = exn_msg (SOME ctxt) exn

       | exn_msg ctxt (Exn.EXCEPTIONS (exns, "")) = cat_lines (map (exn_msg ctxt) exns)

       | exn_msg ctxt (Exn.EXCEPTIONS (exns, msg)) = cat_lines (map (exn_msg ctxt) exns @ [msg])

       | exn_msg ctxt (EXCURSION_FAIL (exn, loc)) =

           exn_msg ctxt exn ^ Markup.markup Markup.location ("\n" ^ loc)

       | exn_msg _ TERMINATE = "Exit."

       | exn_msg _ Interrupt = "Interrupt."

       | exn_msg _ TimeLimit.TimeOut = "Timeout."

       | exn_msg _ TOPLEVEL_ERROR = "Error."

       | exn_msg _ (SYS_ERROR msg) = "## SYSTEM ERROR ##\n" ^ msg

       | exn_msg _ (ERROR msg) = msg

       | exn_msg _ (Fail msg) = raised "Fail" [msg]

       | exn_msg _ (THEORY (msg, thys)) =

           raised "THEORY" (msg :: (if detailed then map Context.str_of_thy thys else []))

       | exn_msg _ (Syntax.AST (msg, asts)) = raised "AST" (msg ::

             (if detailed then map (Pretty.string_of o Syntax.pretty_ast) asts else []))

       | exn_msg ctxt (TYPE (msg, Ts, ts)) = raised "TYPE" (msg ::

             (if detailed then

               if_context ctxt Syntax.string_of_typ Ts @ if_context ctxt Syntax.string_of_term ts

              else []))

       | exn_msg ctxt (TERM (msg, ts)) = raised "TERM" (msg ::

             (if detailed then if_context ctxt Syntax.string_of_term ts else []))

       | exn_msg ctxt (THM (msg, i, thms)) = raised ("THM " ^ string_of_int i) (msg ::

             (if detailed then if_context ctxt ProofContext.string_of_thm thms else []))

       | exn_msg _ exn = raised (General.exnMessage exn) []

   in exn_msg NONE e end;

 end;

 (* controlled execution *)

 local

 fun debugging f x =

   if ! debug then exception_trace (fn () => f x)

   else f x;

 fun toplevel_error f x =

   let val ctxt = try ML_Context.the_local_context () in

     f x handle exn =>

       (Output.error_msg (exn_message (exn_context ctxt exn)); raise TOPLEVEL_ERROR)

   end;

 in

 fun controlled_execution f =

   f

   |> debugging

   |> interruptible;

 fun program f =

  (f

   |> debugging

   |> toplevel_error) ();

 end;

 (* node transactions -- maintaining stable checkpoints *)

 local

 fun is_draft_theory (Theory (gthy, _)) = Context.is_draft (Context.theory_of gthy)

   | is_draft_theory _ = false;

 fun is_stale state = Context.is_stale (theory_of state) handle UNDEF => false;

 fun stale_error NONE = SOME (ERROR "Stale theory encountered after successful execution!")

   | stale_error some = some;

 fun map_theory f (Theory (gthy, ctxt)) =

       Theory (Context.mapping f (LocalTheory.raw_theory f) gthy, ctxt)

   | map_theory _ node = node;

 in

 fun apply_transaction pos f (node, exit) =

   let

     val _ = is_draft_theory node andalso error "Illegal draft theory in toplevel state";

     val cont_node = reset_presentation node;

     val back_node = map_theory (Theory.checkpoint o Theory.copy) cont_node;

     fun state_error e nd = (State (SOME (nd, exit), SOME (node, exit)), e);

     val (result, err) =

       cont_node

       |> controlled_execution f

       |> map_theory Theory.checkpoint

       |> state_error NONE

       handle exn => state_error (SOME exn) cont_node;

     val (result', err') =

       if is_stale result then state_error (stale_error err) back_node

       else (result, err);

   in

     (case err' of

       NONE => result'

     | SOME exn => raise FAILURE (result', exn))

   end;

 end;

 (* primitive transitions *)

 datatype trans =

   Init of string * (bool -> theory) * (theory -> unit) | (*theory name, init, exit*)

   Exit |                                         (*formal exit of theory -- without committing*)

   CommitExit |                                   (*exit and commit final theory*)

   Keep of bool -> state -> unit |                (*peek at state*)

   Transaction of bool -> node -> node;           (*node transaction*)

 local

 fun apply_tr int _ (Init (_, f, exit)) (State (NONE, _)) =

       State (SOME (Theory (Context.Theory (Theory.checkpoint (f int)), NONE), exit), NONE)

   | apply_tr _ _ Exit (State (prev as SOME (Theory (Context.Theory _, _), _), _)) =

       State (NONE, prev)

   | apply_tr _ _ CommitExit (State (NONE, SOME (Theory (Context.Theory thy, _), exit))) =

       (controlled_execution exit thy; toplevel)

   | apply_tr int _ (Keep f) state =

       controlled_execution (fn x => tap (f int) x) state

   | apply_tr int pos (Transaction f) (State (SOME state, _)) =

       apply_transaction pos (fn x => f int x) state

   | apply_tr _ _ _ _ = raise UNDEF;

 fun apply_union _ _ [] state = raise FAILURE (state, UNDEF)

   | apply_union int pos (tr :: trs) state =

       apply_tr int pos tr state

         handle UNDEF => apply_union int pos trs state

           | FAILURE (alt_state, UNDEF) => apply_union int pos trs alt_state

           | exn as FAILURE _ => raise exn

           | exn => raise FAILURE (state, exn);

 in

 fun apply_trans int pos trs state = (apply_union int pos trs state, NONE)

   handle FAILURE (alt_state, exn) => (alt_state, SOME exn) | exn => (state, SOME exn);

 end;

 (* datatype transition *)

 datatype transition = Transition of

  {name: string,              (*command name*)

   pos: Position.T,           (*source position*)

   int_only: bool,            (*interactive-only*)

   print: bool,               (*print result state*)

   no_timing: bool,           (*suppress timing*)

   trans: trans list};        (*primitive transitions (union)*)

 fun make_transition (name, pos, int_only, print, no_timing, trans) =

   Transition {name = name, pos = pos, int_only = int_only, print = print, no_timing = no_timing,

     trans = trans};

 fun map_transition f (Transition {name, pos, int_only, print, no_timing, trans}) =

   make_transition (f (name, pos, int_only, print, no_timing, trans));

 val empty = make_transition ("", Position.none, false, false, false, []);

 (* diagnostics *)

 fun init_of (Transition {trans = [Init (name, _, _)], ...}) = SOME name

   | init_of _ = NONE;

 fun name_of (Transition {name, ...}) = name;

 fun str_of (Transition {name, pos, ...}) = quote name ^ Position.str_of pos;

 fun command_msg msg tr = msg ^ "command " ^ str_of tr;

 fun at_command tr = command_msg "At " tr ^ ".";

 fun type_error tr state =

   ERROR (command_msg "Illegal application of " tr ^ " " ^ str_of_state state);

 (* modify transitions *)

 fun name nm = map_transition (fn (_, pos, int_only, print, no_timing, trans) =>

   (nm, pos, int_only, print, no_timing, trans));

 fun position pos = map_transition (fn (name, _, int_only, print, no_timing, trans) =>

   (name, pos, int_only, print, no_timing, trans));

 fun interactive int_only = map_transition (fn (name, pos, _, print, no_timing, trans) =>

   (name, pos, int_only, print, no_timing, trans));

 val no_timing = map_transition (fn (name, pos, int_only, print, _, trans) =>

   (name, pos, int_only, print, true, trans));

 fun add_trans tr = map_transition (fn (name, pos, int_only, print, no_timing, trans) =>

   (name, pos, int_only, print, no_timing, trans @ [tr]));

 val print = map_transition (fn (name, pos, int_only, _, no_timing, trans) =>

   (name, pos, int_only, true, no_timing, trans));

 (* basic transitions *)

 fun init_theory name f exit = add_trans (Init (name, f, exit));

 val exit = add_trans Exit;

 val keep' = add_trans o Keep;

 fun transaction f = add_trans (Transaction f);

 fun keep f = add_trans (Keep (fn _ => f));

 fun imperative f = keep (fn _ => f ());

 val unknown_theory = imperative (fn () => warning "Unknown theory context");

 val unknown_proof = imperative (fn () => warning "Unknown proof context");

 val unknown_context = imperative (fn () => warning "Unknown context");

 (* theory transitions *)

 fun generic_theory f = transaction (fn _ =>

   (fn Theory (gthy, _) => Theory (f gthy, NONE)

     | _ => raise UNDEF));

 fun theory' f = transaction (fn int =>

   (fn Theory (Context.Theory thy, _) => Theory (Context.Theory (f int thy), NONE)

     | _ => raise UNDEF));

 fun theory f = theory' (K f);

 fun begin_local_theory begin f = transaction (fn _ =>

   (fn Theory (Context.Theory thy, _) =>

         let

           val lthy = f thy;

           val gthy = if begin then Context.Proof lthy else Context.Theory (loc_exit lthy);

         in Theory (gthy, SOME lthy) end

     | _ => raise UNDEF));

 val end_local_theory = transaction (fn _ =>

   (fn Theory (Context.Proof lthy, _) => Theory (Context.Theory (loc_exit lthy), SOME lthy)

     | _ => raise UNDEF));

 local

 fun local_theory_presentation loc f g = transaction (fn int =>

   (fn Theory (gthy, _) =>

         let

           val finish = loc_finish loc gthy;

           val lthy' = f (loc_begin loc gthy);

         in Theory (finish lthy', SOME lthy') end

     | _ => raise UNDEF) #> tap (g int));

 in

 fun local_theory loc f = local_theory_presentation loc f (K I);

 fun present_local_theory loc g = local_theory_presentation loc I g;

 end;

 (* proof transitions *)

 fun end_proof f = transaction (fn int =>

   (fn Proof (prf, (finish, _)) =>

         let val state = ProofNode.current prf in

           if can (Proof.assert_bottom true) state then

             let

               val ctxt' = f int state;

               val gthy' = finish ctxt';

             in Theory (gthy', SOME ctxt') end

           else raise UNDEF

         end

     | SkipProof (0, (gthy, _)) => Theory (gthy, NONE)

     | _ => raise UNDEF));

 local

 fun begin_proof init finish = transaction (fn int =>

   (fn Theory (gthy, _) =>

     let

       val prf = init int gthy;

       val schematic = Proof.schematic_goal prf;

     in

       if ! skip_proofs andalso schematic then

         warning "Cannot skip proof of schematic goal statement"

       else ();

       if ! skip_proofs andalso not schematic then

         SkipProof (0, (finish gthy (Proof.global_skip_proof int prf), gthy))

       else Proof (ProofNode.init prf, (finish gthy, gthy))

     end

   | _ => raise UNDEF));

 in

 fun local_theory_to_proof' loc f = begin_proof

   (fn int => fn gthy => f int (loc_begin loc gthy))

   (loc_finish loc);

 fun local_theory_to_proof loc f = local_theory_to_proof' loc (K f);

 fun theory_to_proof f = begin_proof

   (K (fn Context.Theory thy => f thy | _ => raise UNDEF))

   (K (Context.Theory o ProofContext.theory_of));

 end;

 val forget_proof = transaction (fn _ =>

   (fn Proof (_, (_, orig_gthy)) => Theory (orig_gthy, NONE)

     | SkipProof (_, (_, orig_gthy)) => Theory (orig_gthy, NONE)

     | _ => raise UNDEF));

 fun present_proof f = transaction (fn int =>

   (fn Proof (prf, x) => Proof (ProofNode.apply I prf, x)

     | skip as SkipProof _ => skip

     | _ => raise UNDEF) #> tap (f int));

 fun proofs' f = transaction (fn int =>

   (fn Proof (prf, x) => Proof (ProofNode.applys (f int) prf, x)

     | skip as SkipProof _ => skip

     | _ => raise UNDEF));

 fun proof' f = proofs' (Seq.single oo f);

 val proofs = proofs' o K;

 val proof = proof' o K;

 fun actual_proof f = transaction (fn _ =>

   (fn Proof (prf, x) => Proof (f prf, x)

     | _ => raise UNDEF));

 fun skip_proof f = transaction (fn _ =>

   (fn SkipProof (h, x) => SkipProof (f h, x)

     | _ => raise UNDEF));

 fun skip_proof_to_theory pred = transaction (fn _ =>

   (fn SkipProof (d, (gthy, _)) => if pred d then Theory (gthy, NONE) else raise UNDEF

   | _ => raise UNDEF));

 (** toplevel transactions **)

 (* identification *)

 fun get_id (Transition {pos, ...}) = Position.get_id pos;

 fun put_id id (tr as Transition {pos, ...}) = position (Position.put_id id pos) tr;

 (* thread position *)

 fun setmp_thread_position (Transition {pos, ...}) f x =

   Position.setmp_thread_data pos f x;

 fun status tr m =

   setmp_thread_position tr (fn () => Output.status (Markup.markup m "")) ();

 fun error_msg tr exn_info =

   setmp_thread_position tr (fn () => Output.error_msg (exn_message (EXCURSION_FAIL exn_info))) ();

 (* apply transitions *)

 local

 fun app int (tr as Transition {trans, pos, int_only, print, no_timing, ...}) =

   setmp_thread_position tr (fn state =>

     let

       val _ = if not int andalso int_only then warning (command_msg "Interactive-only " tr) else ();

       fun do_timing f x = (warning (command_msg "" tr); timeap f x);

       fun do_profiling f x = profile (! profiling) f x;

       val (result, status) =

          state |> (apply_trans int pos trans

           |> (if ! profiling > 0 andalso not no_timing then do_profiling else I)

           |> (if ! profiling > 0 orelse ! timing andalso not no_timing then do_timing else I));

       val _ = if int andalso not (! quiet) andalso print then print_state false result else ();

     in (result, Option.map (fn UNDEF => type_error tr state | exn => exn) status) end);

 in

 fun transition int tr st =

   let val ctxt = try context_of st in

     (case app int tr st of

       (_, SOME TERMINATE) => NONE

     | (state', SOME (EXCURSION_FAIL exn_info)) => SOME (state', SOME exn_info)

     | (state', SOME exn) => SOME (state', SOME (exn_context ctxt exn, at_command tr))

     | (state', NONE) => SOME (state', NONE))

   end;

 end;

 (* commit final exit *)

 val commit_exit =

   name "end" empty

   |> add_trans CommitExit

   |> imperative (fn () => warning "Expected to find finished theory");

 (* excursion: toplevel -- apply transformers/presentation -- toplevel *)

 local

 fun no_pr _ _ _ = ();

 fun excur (tr, pr) (st, res) =

   (case transition (! interact) tr st of

     SOME (st', NONE) =>

       (st', setmp_thread_position tr (fn () => pr st st' res) () handle exn =>

         raise EXCURSION_FAIL (exn, "Presentation failed\n" ^ at_command tr))

   | SOME (st', SOME exn_info) => raise EXCURSION_FAIL exn_info

   | NONE => raise EXCURSION_FAIL (TERMINATE, at_command tr));

 fun excurs trs st_res =

   let val (st', res') = fold excur trs st_res in

     if is_toplevel st' then (excur (commit_exit, no_pr) (st', ()); res')

     else error "Unfinished development at end of input"

   end;

 in

 fun present_excursion trs res =

   excurs trs (toplevel, res) handle exn => error (exn_message exn);

 fun excursion trs = present_excursion (map (rpair no_pr) trs) ();

 end;

 end;