(*  Title:      Pure/Isar/toplevel.ML

    ID:         $Id$

    Author:     Markus Wenzel, TU Muenchen

The Isabelle/Isar toplevel.

*)

signature TOPLEVEL =

sig

  exception UNDEF

  type node

  val theory_node: node -> theory option

  val proof_node: node -> ProofHistory.T option

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

  val body_context_node: 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 assert: bool -> unit

  val node_history_of: state -> node History.T

  val node_of: state -> node

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

  val context_of: state -> Context.generic

  val theory_of: state -> theory

  val proof_of: state -> Proof.state

  val proof_position_of: state -> int

  val enter_forward_proof: state -> Proof.state

  val prompt_state_default: state -> string

  val prompt_state_fn: (state -> string) ref

  val print_state_context: state -> unit

  val print_state_default: bool -> state -> unit

  val print_state_hook: (bool -> state -> unit) -> unit

  val print_state_fn: (bool -> state -> unit) ref

  val print_state: bool -> state -> unit

  val pretty_state: bool -> state -> Pretty.T list

  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 RESTART

  val exn_message: exn -> string

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

  val checkpoint: state -> state

  val copy: state -> state

  type transition

  val undo_limit: bool -> int option

  val empty: transition

  val name_of: transition -> string

  val source_of: transition -> OuterLex.token list option

  val name: string -> transition -> transition

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

  val source: OuterLex.token list -> transition -> transition

  val interactive: bool -> transition -> transition

  val print: transition -> transition

  val print': string -> transition -> transition

  val three_buffersN: string

  val print3: transition -> transition

  val no_timing: transition -> transition

  val reset: transition -> transition

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

  val exit: transition -> transition

  val kill: transition -> transition

  val history: (node History.T -> node History.T) -> transition -> transition

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

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

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

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

    -> transition -> transition

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

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

  val theory_context: (theory -> Proof.context * theory) -> transition -> transition

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

    transition -> transition

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

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

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

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

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

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

  val skip_proof: (int History.T -> int History.T) -> transition -> transition

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

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

  val proof_to_theory_context: (bool -> Proof.state -> Proof.context * theory)

    -> transition -> transition

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

  val forget_proof: transition -> transition

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

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

  val unknown_theory: transition -> transition

  val unknown_proof: transition -> transition

  val unknown_context: transition -> transition

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

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

  val excursion: transition list -> unit

  val set_state: state -> unit

  val get_state: unit -> state

  val exn: unit -> (exn * string) option

  val >> : transition -> bool

  val >>> : transition list -> unit

  type 'a isar

  val loop: 'a isar -> unit

end;

structure Toplevel: TOPLEVEL =

struct

(** toplevel state **)

exception UNDEF;

(* datatype state *)

datatype node =

  Theory of theory * Proof.context option |        (*theory with optional body context*)

  Proof of ProofHistory.T * theory |               (*history of proof states, original theory*)

  SkipProof of (int History.T * theory) * theory;

    (*history of proof depths, resulting theory, original theory*)

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

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

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

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

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

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

  | body_context_node (SOME node) loc =

      node |> cases_node (LocalTheory.init loc)

       (if is_some loc then LocalTheory.init loc o Proof.theory_of

        else Proof.context_of)

  | body_context_node NONE _ = raise UNDEF;

datatype state = State of (node History.T * ((node -> unit) * (node -> unit))) option;

val toplevel = State NONE;

fun is_toplevel (State NONE) = true

  | is_toplevel _ = false;

fun level (State NONE) = 0

  | level (State (SOME (node, _))) =

      (case History.current node of

        Theory _ => 0

      | Proof (prf, _) => Proof.level (ProofHistory.current prf)

      | SkipProof ((h, _), _) => History.current h + 1);    (*different notion of proof depth!*)

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

  | str_of_state (State (SOME (node, _))) =

      (case History.current node of

        Theory _ => "in theory mode"

      | Proof _ => "in proof mode"

      | SkipProof _ => "in skipped proof mode");

(* top node *)

fun assert true = ()

  | assert false = raise UNDEF;

fun node_history_of (State NONE) = raise UNDEF

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

val node_of = History.current o node_history_of;

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.Theory (Context.Proof o Proof.context_of);

val theory_of = node_case I Proof.theory_of;

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

fun proof_position_of state =

  (case node_of state of

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

  | _ => raise UNDEF);

val enter_forward_proof = node_case (Proof.init o ProofContext.init) Proof.enter_forward;

(* prompt state *)

fun prompt_state_default (State _) = Source.default_prompt;

val prompt_state_fn = ref prompt_state_default;

fun prompt_state state = ! prompt_state_fn state;

(* print state *)

fun pretty_context thy = [Pretty.block

  [Pretty.str "theory", Pretty.brk 1, Pretty.str (Context.theory_name thy),

    Pretty.str " =", Pretty.brk 1, ThyInfo.pretty_theory thy]];

fun pretty_state_context state =

  (case try theory_of state of NONE => []

  | SOME thy => pretty_context thy);

fun pretty_node prf_only (Theory (thy, _)) = if prf_only then [] else pretty_context thy

  | pretty_node _ (Proof (prf, _)) =

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

  | pretty_node _ (SkipProof ((h, _), _)) =

      [Pretty.str ("skipped proof: depth " ^ string_of_int (History.current h))];

fun pretty_state prf_only state =

  let val ref (begin_state, end_state, _) = Display.current_goals_markers in

    (case try node_of state of NONE => []

    | SOME node =>

        (if begin_state = "" then [] else [Pretty.str begin_state]) @

        pretty_node prf_only node @

        (if end_state = "" then [] else [Pretty.str end_state]))

  end;

val print_state_context = Pretty.writelns o pretty_state_context;

fun print_state_default prf_only state = Pretty.writelns (pretty_state prf_only state);

val print_state_hooks = ref ([]: (bool -> state -> unit) list);

fun print_state_hook f = change print_state_hooks (cons f);

val print_state_fn = ref print_state_default;

fun print_state prf_only state =

 (List.app (fn f => (try (fn () => f prf_only state) (); ())) (! print_state_hooks);

  ! print_state_fn prf_only state);

(** toplevel transitions **)

val quiet = ref false;

val debug = ref false;

val interact = ref false;

val timing = Output.timing;

val profiling = ref 0;

val skip_proofs = ref false;

exception TERMINATE;

exception RESTART;

exception EXCURSION_FAIL of exn * string;

exception FAILURE of state * exn;

(* print exceptions *)

local

fun with_context f xs =

  (case Context.get_context () of NONE => []

  | SOME thy => map (f thy) xs);

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

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

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

fun exn_msg _ TERMINATE = "Exit."

  | exn_msg _ RESTART = "Restart."

  | exn_msg _ Interrupt = "Interrupt."

  | exn_msg _ Output.TOPLEVEL_ERROR = "Error."

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

  | exn_msg _ (ERROR msg) = msg

  | exn_msg detailed (EXCEPTION (exn, msg)) = cat_lines [exn_msg detailed exn, msg]

  | exn_msg detailed (EXCURSION_FAIL (exn, msg)) = cat_lines [exn_msg detailed exn, msg]

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

  | exn_msg true (THEORY (msg, thys)) = raised "THEORY" (msg :: map Context.str_of_thy thys)

  | exn_msg detailed (MetaSimplifier.SIMPROC_FAIL (name, exn)) =

      fail_msg detailed "simproc" ((name, Position.none), exn)

  | exn_msg detailed (Attrib.ATTRIB_FAIL info) = fail_msg detailed "attribute" info

  | exn_msg detailed (Method.METHOD_FAIL info) = fail_msg detailed "method" info

  | exn_msg detailed (Antiquote.ANTIQUOTE_FAIL info) = fail_msg detailed "antiquotation" info

  | exn_msg false (Syntax.AST (msg, _)) = raised "AST" [msg]

  | exn_msg true (Syntax.AST (msg, asts)) =

      raised "AST" (msg :: map (Pretty.string_of o Syntax.pretty_ast) asts)

  | exn_msg false (TYPE (msg, _, _)) = raised "TYPE" [msg]

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

        with_context Sign.string_of_typ Ts @ with_context Sign.string_of_term ts)

  | exn_msg false (TERM (msg, _)) = raised "TERM" [msg]

  | exn_msg true (TERM (msg, ts)) = raised "TERM" (msg :: with_context Sign.string_of_term ts)

  | exn_msg false (THM (msg, _, _)) = raised "THM" [msg]

  | exn_msg true (THM (msg, i, thms)) =

      raised ("THM " ^ string_of_int i) (msg :: map Display.string_of_thm thms)

  | exn_msg _ Option.Option = raised "Option" []

  | exn_msg _ Library.UnequalLengths = raised "UnequalLengths" []

  | exn_msg _ Empty = raised "Empty" []

  | exn_msg _ Subscript = raised "Subscript" []

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

  | exn_msg _ exn = General.exnMessage exn

and fail_msg detailed kind ((name, pos), exn) =

  "Error in " ^ kind ^ " " ^ quote name ^ Position.str_of pos ^ ":\n" ^ exn_msg detailed exn;

in

fun exn_message exn = exn_msg (! debug) exn;

fun print_exn NONE = ()

  | print_exn (SOME (exn, s)) = Output.error_msg (cat_lines [exn_message exn, s]);

end;

(* controlled execution *)

local

fun debugging f x =

  if ! debug then

    setmp Library.do_transform_failure false

      exception_trace (fn () => f x)

  else f x;

fun interruptible f x =

  let val y = ref x

  in raise_interrupt (fn () => y := f x) (); ! y end;

in

fun controlled_execution f =

  f

  |> debugging

  |> interruptible

  |> setmp Output.do_toplevel_errors false;

fun program f =

  Output.ML_errors (fn () => debugging f () handle exn => error (exn_message exn)) ();

end;

(* node transactions and recovery from stale theories *)

(*NB: proof commands should be non-destructive!*)

local

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

val stale_theory = ERROR "Stale theory encountered after succesful execution!";

fun checkpoint_node (Theory (thy, _)) = Theory (Theory.checkpoint thy, NONE)

  | checkpoint_node node = node;

fun copy_node (Theory (thy, _)) = Theory (Theory.copy thy, NONE)

  | copy_node node = node;

fun return (result, NONE) = result

  | return (result, SOME exn) = raise FAILURE (result, exn);

in

fun transaction hist f (node, term) =

  let

    val cont_node = History.map checkpoint_node node;

    val back_node = History.map copy_node cont_node;

    fun state nd = State (SOME (nd, term));

    fun normal_state nd = (state nd, NONE);

    fun error_state nd exn = (state nd, SOME exn);

    val (result, err) =

      cont_node

      |> (f

          |> (if hist then History.apply_copy copy_node else History.map)

          |> controlled_execution)

      |> normal_state

      handle exn => error_state cont_node exn;

  in

    if is_stale result

    then return (error_state back_node (the_default stale_theory err))

    else return (result, err)

  end;

fun mapping f (State (SOME (node, term))) = State (SOME (History.map f node, term))

  | mapping _ state = state;

val checkpoint = mapping checkpoint_node;

val copy = mapping copy_node;

end;

(* primitive transitions *)

(*Note: Recovery from stale theories is provided only for theory-level

  operations via Transaction.  Other node or state operations should

  not touch theories at all.  Interrupts are enabled only for Keep and

  Transaction.*)

datatype trans =

  Reset |                                               (*empty toplevel*)

  Init of (bool -> node) * ((node -> unit) * (node -> unit)) |

                                                        (*init node; with exit/kill operation*)

  Exit |                                                (*conclude node*)

  Kill |                                                (*abort node*)

  History of node History.T -> node History.T |         (*history operation (undo etc.)*)

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

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

fun undo_limit int = if int then NONE else SOME 0;

local

fun apply_tr _ Reset _ = toplevel

  | apply_tr int (Init (f, term)) (State NONE) =

      State (SOME (History.init (undo_limit int) (f int), term))

  | apply_tr _ (Init _ ) (State (SOME _)) = raise UNDEF

  | apply_tr _ Exit (State NONE) = raise UNDEF

  | apply_tr _ Exit (State (SOME (node, (exit, _)))) =

      (exit (History.current node); State NONE)

  | apply_tr _ Kill (State NONE) = raise UNDEF

  | apply_tr _ Kill (State (SOME (node, (_, kill)))) =

      (kill (History.current node); State NONE)

  | apply_tr _ (History _) (State NONE) = raise UNDEF

  | apply_tr _ (History f) (State (SOME (node, term))) = State (SOME (f node, term))

  | apply_tr int (Keep f) state =

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

  | apply_tr _ (Transaction _) (State NONE) = raise UNDEF

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

      transaction hist (fn x => f int x) state;

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

  | apply_union int (tr :: trs) state =

      apply_tr int tr state

        handle UNDEF => apply_union int trs state

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

          | exn as FAILURE _ => raise exn

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

in

fun apply_trans int trs state = (apply_union int 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*)

  source: OuterLex.token list option,  (*source text*)

  int_only: bool,                      (*interactive-only*)

  print: string list,                  (*print modes (union)*)

  no_timing: bool,                     (*suppress timing*)

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

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

  Transition {name = name, pos = pos, source = source,

    int_only = int_only, print = print, no_timing = no_timing, trans = trans};

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

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

val empty = make_transition ("<unknown>", Position.none, NONE, false, [], false, []);

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

fun source_of (Transition {source, ...}) = source;

(* diagnostics *)

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

fun command_msg msg tr = msg ^ "command " ^ str_of_transition 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, source, int_only, print, no_timing, trans) =>

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

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

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

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

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

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

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

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

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

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

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

fun print' mode = map_transition (fn (name, pos, source, int_only, print, no_timing, trans) =>

  (name, pos, source, int_only, insert (op =) mode print, no_timing, trans));

val print = print' "";

val three_buffersN = "three_buffers";

val print3 = print' three_buffersN;

(* build transitions *)

val reset = add_trans Reset;

fun init f exit kill = add_trans (Init (f, (exit, kill)));

val exit = add_trans Exit;

val kill = add_trans Kill;

val history = add_trans o History;

val keep' = add_trans o Keep;

fun map_current f = add_trans (Transaction (false, f));

fun app_current f = add_trans (Transaction (true, f));

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

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

fun init_theory f exit kill =

  init (fn int => Theory (f int, NONE))

    (fn Theory (thy, _) => exit thy | _ => raise UNDEF)

    (fn Theory (thy, _) => kill thy | _ => raise UNDEF);

(* typed transitions *)

fun theory f = app_current

  (K (fn Theory (thy, _) => Theory (f thy, NONE) | _ => raise UNDEF));

fun theory' f = app_current (fn int =>

  (fn Theory (thy, _) => Theory (f int thy, NONE) | _ => raise UNDEF));

fun theory_context f = app_current

  (K (fn Theory (thy, _) => Theory (swap (apfst SOME (f thy))) | _ => raise UNDEF));

fun local_theory loc f = theory_context (LocalTheory.mapping loc f);

fun theory_to_proof f = app_current (fn int =>

  (fn Theory (thy, _) =>

    let

      val prf = f thy;

      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 ((History.init (undo_limit int) 0, #2 (Proof.global_skip_proof int prf)), thy)

      else Proof (ProofHistory.init (undo_limit int) prf, thy)

    end

  | _ => raise UNDEF));

fun proofs' f = map_current (fn int =>

  (fn Proof (prf, orig_thy) => Proof (ProofHistory.applys (f int) prf, orig_thy)

    | SkipProof ((h, thy), orig_thy) => SkipProof ((History.apply I h, thy), orig_thy)

    | _ => raise UNDEF));

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

val proofs = proofs' o K;

val proof = proof' o K;

fun actual_proof f = map_current (fn _ =>

  (fn Proof (prf, orig_thy) => Proof (f prf, orig_thy) | _ => raise UNDEF));

fun skip_proof f = map_current (fn _ =>

  (fn SkipProof ((h, thy), orig_thy) => SkipProof ((f h, thy), orig_thy) | _ => raise UNDEF));

fun end_proof f = map_current (fn int =>

  (fn Proof (prf, _) => Theory (f int (ProofHistory.current prf))

    | SkipProof ((h, thy), _) => if History.current h = 0 then Theory (thy, NONE) else raise UNDEF

    | _ => raise UNDEF));

val forget_proof = map_current (fn _ =>

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

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

    | _ => raise UNDEF));

fun proof_to_theory' f = end_proof (rpair NONE oo f);

fun proof_to_theory f = proof_to_theory' (K f);

fun proof_to_theory_context f = end_proof ((swap o apfst SOME) oo f);

fun skip_proof_to_theory p = map_current (fn _ =>

  (fn SkipProof ((h, thy), _) =>

    if p (History.current h) then Theory (thy, NONE)

    else raise UNDEF

  | _ => raise UNDEF));

fun present_local_theory loc f = app_current (fn int =>

  (fn Theory (thy, _) => Theory (swap (apfst SOME (LocalTheory.mapping loc I thy)))

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

fun present_proof f = map_current (fn int =>

  (fn node as Proof _ => node | _ => raise UNDEF) #> tap (f int));

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");

(** toplevel transactions **)

(* apply transitions *)

local

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

  let

    val _ = conditional (not int andalso int_only) (fn () =>

      warning (command_msg "Interactive-only " tr));

    fun do_timing f x = (Output.info (command_msg "" tr); timeap f x);

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

    val (result, opt_exn) =

       state |> (apply_trans int trans

        |> (if ! profiling > 0 then do_profiling else I)

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

    val _ = conditional (int andalso not (! quiet) andalso

        exists (fn m => m mem_string print) ("" :: ! print_mode))

      (fn () => print_state false result);

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

in

fun apply int tr st =

  (case app int tr st of

    (_, SOME TERMINATE) => NONE

  | (_, SOME RESTART) => SOME (toplevel, NONE)

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

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

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

end;

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

local

fun excur [] x = x

  | excur ((tr, pr) :: trs) (st, res) =

      (case apply (! interact) tr st of

        SOME (st', NONE) =>

          excur trs (st', 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 no_pr _ _ _ = ();

in

fun present_excursion trs res =

  (case excur trs (State NONE, res) of

    (State NONE, res') => res'

  | _ => error "Unfinished development at end of input")

  handle exn => error (exn_message exn);

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

end;

(** interactive transformations **)

(* the global state reference *)

val global_state = ref (toplevel, NONE: (exn * string) option);

fun set_state state = global_state := (state, NONE);

fun get_state () = fst (! global_state);

fun exn () = snd (! global_state);

(* the Isar source of transitions *)

type 'a isar =

  (transition, (transition option,

    (OuterLex.token, (OuterLex.token option, (OuterLex.token, (OuterLex.token,

      Position.T * (Symbol.symbol, (string, 'a) Source.source) Source.source)

          Source.source) Source.source) Source.source) Source.source) Source.source) Source.source;

(* apply transformers to global state *)

nonfix >> >>>;

fun >> tr =

  (case apply true tr (get_state ()) of

    NONE => false

  | SOME (state', exn_info) =>

      (global_state := (state', exn_info);

        print_exn exn_info;

        true));

fun >>> [] = ()

  | >>> (tr :: trs) = if >> tr then >>> trs else ();

(*Spurious interrupts ahead!  Race condition?*)

fun get_interrupt src = SOME (Source.get_single src) handle Interrupt => NONE;

fun raw_loop src =

  (case get_interrupt (Source.set_prompt (prompt_state (get_state ())) src) of

    NONE => (writeln "\nInterrupt."; raw_loop src)

  | SOME NONE => ()

  | SOME (SOME (tr, src')) => if >> tr then raw_loop src' else ());

fun loop src = ignore_interrupt raw_loop src;

end;