Mise à jour terminée. Pour connaître les apports de la version 13.8.4 par rapport à notre ancienne version vous pouvez lire les "Release Notes" suivantes :
https://about.gitlab.com/releases/2021/02/11/security-release-gitlab-13-8-4-released/
https://about.gitlab.com/releases/2021/02/05/gitlab-13-8-3-released/

grammar.ml 42.1 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
open UnparameterizedSyntax
open Syntax
open Positions

(* ------------------------------------------------------------------------ *)
(* Precedence levels for tokens or pseudo-tokens alike. *)

module TokPrecedence = struct

  (* This set records, on a token by token basis, whether the token's
     precedence level is ever useful. This allows emitting warnings
     about useless precedence declarations. *)

  let ever_useful : StringSet.t ref =
    ref StringSet.empty

  let use id =
    ever_useful := StringSet.add id !ever_useful

  (* This function is invoked when someone wants to consult a token's
     precedence level. This does not yet mean that this level is
     useful, though. Indeed, if it is subsequently compared against
     [UndefinedPrecedence], it will not allow solving a conflict. So,
     in addition to the desired precedence level, we return a delayed
     computation which, when evaluated, records that this precedence
     level was useful. *)

  let levelip id properties =
29
    lazy (use id), properties.tk_precedence
30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

  let leveli id = 
    let properties =
      try
	StringMap.find id Front.grammar.tokens
      with Not_found ->
	assert false (* well-formedness check has been performed earlier *)
    in
    levelip id properties    

  (* This function is invoked after the automaton has been constructed.
     It warns about unused precedence levels. *)

  let diagnostics () =
    StringMap.iter (fun id properties ->
      if not (StringSet.mem id !ever_useful) then
46
	match properties.tk_precedence with
47 48 49 50
	| UndefinedPrecedence ->
	    ()
	| PrecedenceLevel (_, _, pos1, pos2) ->
	    Error.grammar_warning (Positions.two pos1 pos2)
51
	      "the precedence level assigned to %s is never useful." id
52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
    ) Front.grammar.tokens

end

(* ------------------------------------------------------------------------ *)
(* Nonterminals. *)

module Nonterminal = struct

  type t = int

  let n2i i = i

  let compare = (-)

  (* Determine how many nonterminals we have and build mappings
     both ways between names and indices. A new nonterminal is
     created for every start symbol. *)

  let new_start_nonterminals =
    StringSet.fold (fun symbol ss -> (symbol ^ "'") :: ss) Front.grammar.start_symbols []

  let original_nonterminals =
75
    nonterminals Front.grammar
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128
  
  let start =
    List.length new_start_nonterminals

  let (n : int), (name : string array), (map : int StringMap.t) =
    Misc.index (new_start_nonterminals @ original_nonterminals)

  let () =
    Error.logG 1 (fun f ->
      Printf.fprintf f
	"Grammar has %d nonterminal symbols, among which %d start symbols.\n"
	(n - start) start
    )

  let is_start nt =
    nt < start

  let print normalize nt =
    if normalize then
      Misc.normalize name.(nt)
    else
      name.(nt)

  let lookup name =
    StringMap.find name map

  let positions nt =
    (StringMap.find (print false nt) Front.grammar.rules).positions

  let iter f =
    Misc.iteri n f

  let fold f accu =
    Misc.foldi n f accu

  let map f =
    Misc.mapi n f

  let iterx f =
    for nt = start to n - 1 do
      f nt
    done

  let foldx f accu =
    Misc.foldij start n f accu

  let ocamltype nt =
    assert (not (is_start nt));
    try
      Some (StringMap.find (print false nt) Front.grammar.types)
    with Not_found ->
      None

129 130 131 132 133 134 135 136
  let ocamltype_of_start_symbol nt =
    match ocamltype nt with
    | Some typ ->
        typ
    | None ->
        (* Every start symbol has a type. *)
        assert false

137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155
  let tabulate f =
    Array.get (Array.init n f)

end

(* Sets and maps over nonterminals, used only below. *)

module NonterminalMap = Patricia.Big

module NonterminalSet = Patricia.Big.Domain

(* ------------------------------------------------------------------------ *)
(* Terminals. *)

module Terminal = struct

  type t = int

  let t2i i = i
156
  let i2t i = i
157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172

  let compare = (-)

  let equal (tok1 : t) (tok2 : t) =
    tok1 = tok2

  (* Determine how many terminals we have and build mappings
     both ways between names and indices. A new terminal "#"
     is created. A new terminal "error" is created. The fact
     that the integer code assigned to the "#" pseudo-terminal
     is the last one is exploited in the table-based back-end.
     (The right-most row of the action table is not created.)

     Pseudo-tokens (used in %prec declarations, but never
     declared using %token) are filtered out. *)

POTTIER Francois's avatar
POTTIER Francois committed
173 174 175
  (* In principle, the number of the [error] token is irrelevant.
     It is currently 0, but we do not rely on that. *)

176
  let (n : int), (name : string array), (map : int StringMap.t) =
177
    let tokens = tokens Front.grammar in
178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198
    match tokens with
    | [] ->
	Error.error [] "no tokens have been declared."
    | _ ->
	Misc.index ("error" :: tokens @ [ "#" ])

  let print tok =
    name.(tok)

  let lookup name =
    StringMap.find name map

  let sharp =
    lookup "#"

  let error =
    lookup "error"

  let pseudo tok =
    (tok = sharp) || (tok = error)

POTTIER Francois's avatar
POTTIER Francois committed
199 200 201
  let real t =
    error <> t && t <> sharp

202 203 204 205
  let token_properties = 
    let not_so_dummy_properties = (* applicable to [error] and [#] *)
      {
	tk_filename      = "__primitives__";
206
	tk_precedence    = UndefinedPrecedence;
207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243
	tk_associativity = UndefinedAssoc;
	tk_ocamltype     = None;
	tk_is_declared   = true;
	tk_position      = Positions.dummy;
      }
    in
    Array.init n (fun tok ->
      try 
	 StringMap.find name.(tok) Front.grammar.tokens 
       with Not_found ->
	 assert (tok = sharp || tok = error);
	 not_so_dummy_properties
    )

  let () =
    Error.logG 1 (fun f ->
      Printf.fprintf f "Grammar has %d terminal symbols.\n" (n - 2)
    )

  let precedence_level tok = 
    TokPrecedence.levelip (print tok) token_properties.(tok)

  let associativity tok =
    token_properties.(tok).tk_associativity

  let ocamltype tok =
    token_properties.(tok).tk_ocamltype

  let iter f =
    Misc.iteri n f

  let fold f accu =
    Misc.foldi n f accu

  let map f =
    Misc.mapi n f

244 245
  let () =
    assert (sharp = n - 1)
246
  let mapx f =
247
    Misc.mapi sharp f
248

POTTIER Francois's avatar
POTTIER Francois committed
249 250 251 252 253 254 255
  let () =
    assert (error = 0)
  let iter_real f =
    for i = 1 to n-2 do
      f i
    done

256
  (* If a token named [EOF] exists, then it is assumed to represent
257
     ocamllex's [eof] pattern. *)
258 259 260 261 262 263 264

  let eof =
    try
      Some (lookup "EOF")
    with Not_found ->
      None

265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284
  (* The sub-module [Word] offers an implementation of words (that is,
     sequences) of terminal symbols. It is used by [LRijkstra]. We
     make it a functor, because it has internal state (a hash table)
     and a side effect (failure if there are more than 256 terminal
     symbols). *)

  module Word (X : sig end) = struct

    (* We could use lists, or perhaps the sequences offered by the module
       [Seq], which support constant time concatenation. However, we need a
       much more compact representation: [LRijkstra] stores tens of millions
       of such words. We use strings, because they are very compact (8 bits
       per symbol), and on top of that, we use a hash-consing facility. In
       practice, hash-consing allows us to save 1000x in space. *)

    (* A drawback of this approach is that it works only if the number of
       terminal symbols is at most 256. For the moment, this is good enough.
       [LRijkstra] already has difficulty at 100 terminal symbols or so. *)

    let () =
285
      assert (n <= 256)
286

287 288
    let (encode : string -> int), (decode : int -> string), verbose =
      Misc.new_encode_decode 1024
289 290

    type word =
291
      int
292 293

    let epsilon =
294
      encode ""
295 296

    let singleton t =
297
      encode (String.make 1 (Char.chr t))
298

299 300 301
    let append i1 i2 =
      let w1 = decode i1
      and w2 = decode i2 in
302
      if String.length w1 = 0 then
303
        i2
304
      else if String.length w2 = 0 then
305
        i1
306
      else
307
        encode (w1 ^ w2)
308

309 310
    let length i =
      String.length (decode i)
311

312 313 314
    let first i z =
      let w = decode i in
      if String.length w > 0 then
315 316 317 318 319 320 321 322 323 324
        Char.code w.[0]
      else
        z

    let rec elements i n w =
      if i = n then
        []
      else
        Char.code w.[i] :: elements (i + 1) n w

325 326
    let elements i =
      let w = decode i in
327 328
      elements 0 (String.length w) w

329 330
    let print i =
      let w = decode i in
331 332 333 334
      Misc.separated_iter_to_string
        (fun c -> print (Char.code c))
        " "
        (fun f -> String.iter f w)
335

POTTIER Francois's avatar
POTTIER Francois committed
336
    (* [Pervasives.compare] implements a lexicographic ordering on strings. *)
337 338
    let compare i1 i2 =
      Pervasives.compare (decode i1) (decode i2)
POTTIER Francois's avatar
POTTIER Francois committed
339

340 341
  end

342 343 344 345 346 347 348 349 350 351
end

(* Sets of terminals are used intensively in the LR(1) construction,
   so it is important that they be as efficient as possible. *)

module TerminalSet = struct

  include CompressedBitSet 

  let print toks =
352
    Misc.separated_iter_to_string Terminal.print " " (fun f -> iter f toks)
353 354 355 356 357 358 359 360

  let universe =
    remove Terminal.sharp (
      remove Terminal.error (
        Terminal.fold add empty
      )
    )

361 362 363 364 365 366 367 368 369 370 371 372
  (* The following definitions are used in the computation of FIRST sets
     below. They are not exported outside of this file. *)

  type property =
    t

  let bottom =
    empty

  let is_maximal _ =
    false

373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462
end

(* Maps over terminals. *)

module TerminalMap = Patricia.Big

(* ------------------------------------------------------------------------ *)
(* Symbols. *)

module Symbol = struct

  type t =
    | N of Nonterminal.t
    | T of Terminal.t

  let compare sym1 sym2 =
    match sym1, sym2 with
    | N nt1, N nt2 ->
	Nonterminal.compare nt1 nt2
    | T tok1, T tok2 ->
	Terminal.compare tok1 tok2
    | N _, T _ ->
	1
    | T _, N _ ->
	-1

  let equal sym1 sym2 =
    compare sym1 sym2 = 0

  let rec lequal syms1 syms2 =
    match syms1, syms2 with
    | [], [] ->
	true
    | sym1 :: syms1, sym2 :: syms2 ->
	equal sym1 sym2 && lequal syms1 syms2
    | _ :: _, []
    | [], _ :: _ ->
	false

  let print = function
    | N nt ->
	Nonterminal.print false nt
    | T tok ->
	Terminal.print tok

  let nonterminal = function
    | T _ ->
	false
    | N _ ->
	true

  (* Printing an array of symbols. [offset] is the start offset -- we
     print everything to its right. [dot] is the dot offset -- we
     print a dot at this offset, if we find it. *)

  let printaod offset dot symbols =
    let buffer = Buffer.create 512 in
    let length = Array.length symbols in
    for i = offset to length do
      if i = dot then
	Buffer.add_string buffer ". ";
      if i < length then begin
	Buffer.add_string buffer (print symbols.(i));
	Buffer.add_char buffer ' '
      end
    done;
    Buffer.contents buffer

  let printao offset symbols =
    printaod offset (-1) symbols

  let printa symbols =
    printao 0 symbols

  let printl symbols =
    printa (Array.of_list symbols)

  let lookup name =
    try
      T (Terminal.lookup name)
    with Not_found ->
      try
	N (Nonterminal.lookup name)
      with Not_found ->
	assert false (* well-formedness check has been performed earlier *)

end

(* Sets of symbols. *)

463 464 465 466 467
module SymbolSet = struct

  include Set.Make(Symbol)

  let print symbols =
468
    Symbol.printl (elements symbols)
469 470 471 472 473 474 475 476 477 478 479 480 481 482

  (* The following definitions are used in the computation of symbolic FOLLOW
     sets below. They are not exported outside of this file. *)

  type property =
    t

  let bottom =
    empty

  let is_maximal _ =
    false

end
483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509

(* Maps over symbols. *)

module SymbolMap = struct

  include Map.Make(Symbol)

  let domain m =
    fold (fun symbol _ accu ->
      symbol :: accu
    ) m []

  let purelynonterminal m =
    fold (fun symbol _ accu ->
      accu && Symbol.nonterminal symbol
    ) m true

end

(* ------------------------------------------------------------------------ *)
(* Productions. *)

module Production = struct

  type index =
      int

510 511 512
  let compare =
    (-)

513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562
  (* Create an array of productions. Record which productions are
     associated with every nonterminal. A new production S' -> S
     is created for every start symbol S. It is known as a
     start production. *)

  let n : int =
    let n = StringMap.fold (fun _ { branches = branches } n ->
      n + List.length branches
    ) Front.grammar.rules 0 in
    Error.logG 1 (fun f -> Printf.fprintf f "Grammar has %d productions.\n" n);
    n + StringSet.cardinal Front.grammar.start_symbols

  let p2i prod =
    prod

  let i2p prod =
    assert (prod >= 0 && prod < n);
    prod

  let table : (Nonterminal.t * Symbol.t array) array =
    Array.make n (-1, [||])

  let identifiers : identifier array array =
    Array.make n [||]

  let actions : action option array =
    Array.make n None

  let ntprods : (int * int) array =
    Array.make Nonterminal.n (-1, -1)

  let positions : Positions.t list array =
    Array.make n []

  let (start : int),
      (startprods : index NonterminalMap.t) =
    StringSet.fold (fun nonterminal (k, startprods) ->
      let nt = Nonterminal.lookup nonterminal
      and nt' = Nonterminal.lookup (nonterminal ^ "'") in
      table.(k) <- (nt', [| Symbol.N nt |]);
      identifiers.(k) <- [| "_1" |];
      ntprods.(nt') <- (k, k+1);
      positions.(k) <- Nonterminal.positions nt;
      k+1,
      NonterminalMap.add nt k startprods
    ) Front.grammar.start_symbols (0, NonterminalMap.empty)

  let prec_decl : symbol located option array = 
    Array.make n None

563 564 565 566 567 568
  let production_level : branch_production_level array = 
    (* The start productions should receive this dummy level, I suppose.
       We use a fresh mark, so a reduce/reduce conflict that involves a
       start production will not be solved. *)
    let dummy = ProductionLevel (Mark.fresh(), 0) in
    Array.make n dummy
569 570 571 572 573 574

  let (_ : int) = StringMap.fold (fun nonterminal { branches = branches } k ->
    let nt = Nonterminal.lookup nonterminal in
    let k' = List.fold_left (fun k branch ->
      let symbols = Array.of_list branch.producers in
      table.(k) <- (nt, Array.map (fun (v, _) -> Symbol.lookup v) symbols);
575
      identifiers.(k) <- Array.map snd symbols;
576
      actions.(k) <- Some branch.action;
577
      production_level.(k) <- branch.branch_production_level;
578
      prec_decl.(k) <- branch.branch_prec_annotation;
579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604
      positions.(k) <- [ branch.branch_position ];
      k+1
    ) k branches in
    ntprods.(nt) <- (k, k');
    k'
  ) Front.grammar.rules start

  (* Iteration over the productions associated with a specific
     nonterminal. *)

  let iternt nt f =
    let k, k' = ntprods.(nt) in
    for prod = k to k' - 1 do
      f prod
    done

  let foldnt (nt : Nonterminal.t) (accu : 'a) (f : index -> 'a -> 'a) : 'a =
    let k, k' = ntprods.(nt) in
    let rec loop accu prod =
      if prod < k' then
	loop (f prod accu) (prod + 1)
      else
	accu
    in
    loop accu k

605 606
  (* This funny variant is lazy. If at some point [f] does not demand its
     second argument, then iteration stops. *)
607
  let foldnt_lazy (nt : Nonterminal.t) (f : index -> (unit -> 'a) -> 'a) (seed : 'a) : 'a =
608 609 610
    let k, k' = ntprods.(nt) in
    let rec loop prod seed =
      if prod < k' then
611
        f prod (fun () -> loop (prod + 1) seed)
612 613 614 615 616
      else
        seed
    in
    loop k seed

617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677
  (* Accessors. *)

  let def prod =
    table.(prod)

  let nt prod =
    let nt, _ = table.(prod) in
    nt

  let rhs prod =
    let _, rhs = table.(prod) in
    rhs

  let length prod =
    Array.length (rhs prod)

  let identifiers prod =
    identifiers.(prod)

  let is_start prod =
    prod < start

  let classify prod =
    if is_start prod then
      match (rhs prod).(0) with
      | Symbol.N nt ->
	  Some nt
      | Symbol.T _ ->
	  assert false
    else
      None

  let action prod =
    match actions.(prod) with
    | Some action ->
	action
    | None ->
	(* Start productions have no action. *)
	assert (is_start prod);
	assert false

  let positions prod =
    positions.(prod)

  let startsymbol2startprod nt =
    try
      NonterminalMap.find nt startprods
    with Not_found ->
      assert false (* [nt] is not a start symbol *)

  (* Iteration. *)

  let iter f =
    Misc.iteri n f

  let fold f accu =
    Misc.foldi n f accu

  let map f =
    Misc.mapi n f

POTTIER Francois's avatar
POTTIER Francois committed
678 679 680
  let amap f =
    Array.init n f

681 682 683 684 685 686 687 688
  let iterx f =
    for prod = start to n - 1 do
      f prod
    done

  let foldx f accu =
    Misc.foldij start n f accu

689 690 691
  let mapx f =
    Misc.mapij start n f

692 693 694 695 696 697 698 699 700 701 702 703 704 705 706
  (* Printing a production. *)

  let print prod =
    assert (not (is_start prod));
    let nt, rhs = table.(prod) in
    Printf.sprintf "%s -> %s" (Nonterminal.print false nt) (Symbol.printao 0 rhs)

  (* Tabulation. *)

  let tabulate f =
    Misc.tabulate n f

  let tabulateb f =
    Misc.tabulateb n f

707 708 709
  (* This array allows recording, for each %prec declaration, whether it is
     ever useful. This allows us to emit a warning about useless %prec
     declarations. *)
710

711 712 713 714 715 716 717 718 719 720
  (* 2015/10/06: We take into account the fact that a %prec declaration can be
     duplicated by inlining or by the expansion of parameterized non-terminal
     symbols. Our table is not indexed by productions, but by positions (of
     %prec declarations in the source). Thus, if a %prec declaration is
     duplicated, at least one of its copies should be found useful for the
     warning to be suppressed. *)

  let ever_useful : (Positions.t, unit) Hashtbl.t =
    (* assuming that generic hashing and equality on positions are OK *)
    Hashtbl.create 16
721 722

  let consult_prec_decl prod =
723 724 725 726 727 728 729 730 731
    let osym = prec_decl.(prod) in
    lazy (
      Option.iter (fun sym ->
        (* Mark this %prec declaration as useful. *)
        let pos = Positions.position sym in
        Hashtbl.add ever_useful pos ()
      ) osym
    ),
    osym
732 733 734

  let diagnostics () =
    iterx (fun prod ->
735 736 737 738 739
      let osym = prec_decl.(prod) in
      Option.iter (fun sym ->
        (* Check whether this %prec declaration was useless. *)
        let pos = Positions.position sym in
        if not (Hashtbl.mem ever_useful pos) then begin
740
          Error.grammar_warning [pos] "this %%prec declaration is never useful.";
741 742 743
          Hashtbl.add ever_useful pos () (* hack: avoid two warnings at the same position *)
        end
      ) osym
744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767
    )

  (* Determining the precedence level of a production. If no %prec
     declaration was explicitly supplied, it is the precedence level
     of the rightmost terminal symbol in the production's right-hand
     side. *)

  type production_level =
    | PNone
    | PRightmostToken of Terminal.t
    | PPrecDecl of symbol

  let rightmost_terminal prod =
    Array.fold_left (fun accu symbol ->
      match symbol with
      | Symbol.T tok ->
	  PRightmostToken tok
      | Symbol.N _ ->
	  accu
    ) PNone (rhs prod)

  let combine e1 e2 =
    lazy (Lazy.force e1; Lazy.force e2)

768
  let precedence prod =
769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805
    let fact1, prec_decl = consult_prec_decl prod in
    let oterminal =
      match prec_decl with
      | None ->
	  rightmost_terminal prod
      | Some { value = terminal } ->
	  PPrecDecl terminal
    in
    match oterminal with
    | PNone ->
	fact1, UndefinedPrecedence
    | PRightmostToken tok ->
	let fact2, level = Terminal.precedence_level tok in
	combine fact1 fact2, level
    | PPrecDecl id ->
	let fact2, level = TokPrecedence.leveli id  in
	combine fact1 fact2, level

end

(* ------------------------------------------------------------------------ *)
(* Maps over productions. *)

module ProductionMap = struct

  include Patricia.Big

  (* Iteration over the start productions only. *)

  let start f =
    Misc.foldi Production.start (fun prod m ->
      add prod (f prod) m
    ) empty

end

(* ------------------------------------------------------------------------ *)
806 807 808
(* If requested, build and print the forward reference graph of the grammar.
   There is an edge of a nonterminal symbol [nt1] to every nonterminal symbol
   [nt2] that occurs in the definition of [nt1]. *)
809 810

let () =
811
  if Settings.graph then begin
812

813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830
    (* Allocate. *)

    let forward : NonterminalSet.t array =
      Array.make Nonterminal.n NonterminalSet.empty
    in

    (* Populate. *)

    Array.iter (fun (nt1, rhs) ->
      Array.iter (function
        | Symbol.T _ ->
            ()
        | Symbol.N nt2 ->
            forward.(nt1) <- NonterminalSet.add nt2 forward.(nt1)
      ) rhs
    ) Production.table;

    (* Print. *)
831 832 833 834 835 836 837 838 839

    let module P = Dot.Print (struct
      type vertex = Nonterminal.t
      let name nt =
	Printf.sprintf "nt%d" nt
      let successors (f : ?style:Dot.style -> label:string -> vertex -> unit) nt =
	NonterminalSet.iter (fun successor ->
	  f ~label:"" successor
	) forward.(nt)
840
      let iter (f : ?shape:Dot.shape -> ?style:Dot.style -> label:string -> vertex -> unit) =
841 842 843 844 845 846 847 848
	Nonterminal.iter (fun nt ->
	  f ~label:(Nonterminal.print false nt) nt
	)
    end) in
    let f = open_out (Settings.base ^ ".dot") in
    P.print f;
    close_out f

849 850
  end

851 852 853 854
(* ------------------------------------------------------------------------ *)
(* Support for analyses of the grammar, expressed as fixed point computations.
   We exploit the generic fixed point algorithm in [Fix]. *)

POTTIER Francois's avatar
POTTIER Francois committed
855 856 857 858 859
(* We perform memoization only at nonterminal symbols. We assume that the
   analysis of a symbol is the analysis of its definition (as opposed to,
   say, a computation that depends on the occurrences of this symbol in
   the grammar). *)

860 861 862 863 864 865 866 867 868 869 870 871 872 873
module GenericAnalysis
  (P : Fix.PROPERTY)
  (S : sig
    open P

    (* An analysis is specified by the following functions. *)

    (* [terminal] maps a terminal symbol to a property. *)
    val terminal: Terminal.t -> property
    
    (* [disjunction] abstracts a binary alternative. That is, when we analyze
       an alternative between several productions, we compute a property for
       each of them independently, then we combine these properties using
       [disjunction]. *)
874
    val disjunction: property -> (unit -> property) -> property
875 876 877 878 879 880 881 882 883

    (* [P.bottom] should be a neutral element for [disjunction]. We use it in
       the analysis of an alternative with zero branches. *)

    (* [conjunction] abstracts a binary sequence. That is, when we analyze a
       sequence, we compute a property for each member independently, then we
       combine these properties using [conjunction]. In general, conjunction
       needs access to the first member of the sequence (a symbol), not just
       to its analysis (a property). *)
884
    val conjunction: Symbol.t -> property -> (unit -> property) -> property
885 886 887 888 889 890 891 892 893 894 895 896

    (* [epsilon] abstracts the empty sequence. It should be a neutral element
       for [conjunction]. *)
    val epsilon: property

  end)
: sig
  open P

  (* The results of the analysis take the following form. *)

  (* To every nonterminal symbol, we associate a property. *)
POTTIER Francois's avatar
POTTIER Francois committed
897 898 899 900
  val nonterminal: Nonterminal.t -> property

  (* To every symbol, we associate a property. *)
  val symbol: Symbol.t -> property
901 902 903 904 905 906 907 908 909 910

  (* To every suffix of every production, we associate a property.
     The offset [i], which determines the beginning of the suffix,
     must be contained between [0] and [n], inclusive, where [n]
     is the length of the production. *)
  val production: Production.index -> int -> property

end = struct
  open P

POTTIER Francois's avatar
POTTIER Francois committed
911 912 913 914 915
  (* The following analysis functions are parameterized over [get], which allows
     making a recursive call to the analysis at a nonterminal symbol. [get] maps
     a nonterminal symbol to a property. *)

  (* Analysis of a symbol. *)
916

POTTIER Francois's avatar
POTTIER Francois committed
917 918 919 920 921 922 923 924 925
  let symbol sym get : property =
    match sym with
    | Symbol.T tok ->
        S.terminal tok
    | Symbol.N nt ->
        (* Recursive call to the analysis, via [get]. *)
        get nt    

  (* Analysis of (a suffix of) a production [prod], starting at index [i]. *)
926

POTTIER Francois's avatar
POTTIER Francois committed
927
  let production prod i get : property =
928 929 930 931 932 933 934 935 936 937
    let rhs = Production.rhs prod in
    let n = Array.length rhs in
    (* Conjunction over all symbols in the right-hand side. This can be viewed
       as a version of [Array.fold_right], which does not necessarily begin at
       index [0]. Note that, because [conjunction] is lazy, it is possible
       to stop early. *)
    let rec loop i =
      if i = n then
        S.epsilon
      else
POTTIER Francois's avatar
POTTIER Francois committed
938 939 940
        let sym = rhs.(i) in
        S.conjunction sym
          (symbol sym get)
941
          (fun () -> loop (i+1))
942 943 944 945 946 947 948
    in
    loop i

  (* The analysis is the least fixed point of the following function, which
     analyzes a nonterminal symbol by looking up and analyzing its definition
     as a disjunction of conjunctions of symbols. *)

POTTIER Francois's avatar
POTTIER Francois committed
949
  let nonterminal nt get : property =
950 951 952 953 954 955 956 957 958 959 960 961
    (* Disjunction over all productions for this nonterminal symbol. *)
    Production.foldnt_lazy nt (fun prod rest ->
      S.disjunction
        (production prod 0 get)
        rest
    ) P.bottom

  (* The least fixed point is taken as follows. Note that it is computed
     on demand, as [lfp] is called by the user. *)

  module F =
    Fix.Make
962
      (Maps.ArrayAsImperativeMaps(Nonterminal))
963 964
      (P)

POTTIER Francois's avatar
POTTIER Francois committed
965 966 967 968
  let nonterminal =
    F.lfp nonterminal

  (* The auxiliary functions can be published too. *)
969

POTTIER Francois's avatar
POTTIER Francois committed
970 971
  let symbol sym =
    symbol sym nonterminal
972

POTTIER Francois's avatar
POTTIER Francois committed
973 974
  let production prod i =
    production prod i nonterminal
975 976 977

end

978 979 980 981 982 983
(* ------------------------------------------------------------------------ *)
(* The computation of FOLLOW sets does not follow the above model. Instead, we
   need to explicitly compute a system of equations over sets of terminal
   symbols (in a first pass), then solve the constraints (in a second
   pass). *)

984 985 986 987
(* The computation of the symbolic FOLLOW sets follows the same pattern, but
   produces sets of symbols, instead of sets of terminals. For this reason,
   we parameterize this little equation solver over a module [P], which we
   later instantiate with [TerminalSet] and [SymbolSet]. *)
988

989 990 991 992
module Solve (P : sig
  include Fix.PROPERTY
  val union: property -> property -> property
end) = struct
993

994
  (* An equation's right-hand side is a set expression. *)
995

996 997 998 999
  type expr =
  | EVar of Nonterminal.t
  | EConstant of P.property
  | EUnion of expr * expr
1000

1001 1002
  (* A system of equations is represented as an array, which maps nonterminal
     symbols to expressions. *)
1003

1004 1005
  type equations =
    expr array
1006

1007
  (* This solver computes the least solution of a set of equations. *)
1008

1009
  let solve (eqs : equations) : Nonterminal.t -> P.property =
1010

1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033
    let rec expr e get =
      match e with
      | EVar nt ->
          get nt
      | EConstant c ->
          c
      | EUnion (e1, e2) ->
          P.union (expr e1 get) (expr e2 get)
    in

    let nonterminal nt get =
      expr eqs.(nt) get
    in

    let module F =
      Fix.Make
        (Maps.ArrayAsImperativeMaps(Nonterminal))
        (P)
    in

    F.lfp nonterminal

end
1034

1035 1036 1037 1038 1039 1040 1041
(* ------------------------------------------------------------------------ *)
(* Compute which nonterminals are nonempty, that is, recognize a
   nonempty language. Also, compute which nonterminals are
   nullable. The two computations are almost identical. The only
   difference is in the base case: a single terminal symbol is not
   nullable, but is nonempty. *)

1042 1043 1044 1045 1046 1047 1048
module NONEMPTY =
  GenericAnalysis
    (Boolean)
    (struct
      (* A terminal symbol is nonempty. *)
      let terminal _ = true
      (* An alternative is nonempty if at least one branch is nonempty. *)
1049
      let disjunction p q = p || q()
1050
      (* A sequence is nonempty if both members are nonempty. *)
1051
      let conjunction _ p q = p && q()
1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063
      (* The sequence epsilon is nonempty. It generates the singleton
         language {epsilon}. *)
      let epsilon = true
     end)

module NULLABLE =
  GenericAnalysis
    (Boolean)
    (struct
      (* A terminal symbol is not nullable. *)
      let terminal _ = false
      (* An alternative is nullable if at least one branch is nullable. *)
1064
      let disjunction p q = p || q()
1065
      (* A sequence is nullable if both members are nullable. *)
1066
      let conjunction _ p q = p && q()
1067 1068 1069
      (* The sequence epsilon is nullable. *)
      let epsilon = true
     end)
1070

1071 1072 1073
(* ------------------------------------------------------------------------ *)
(* Compute FIRST sets. *)

1074 1075 1076 1077 1078 1079 1080
module FIRST =
  GenericAnalysis
    (TerminalSet)
    (struct
      (* A terminal symbol has a singleton FIRST set. *)
      let terminal = TerminalSet.singleton
      (* The FIRST set of an alternative is the union of the FIRST sets. *)
1081
      let disjunction p q = TerminalSet.union p (q())
1082 1083 1084 1085 1086
      (* The FIRST set of a sequence is the union of:
           the FIRST set of the first member, and
           the FIRST set of the second member, if the first member is nullable. *)
      let conjunction symbol p q =
        if NULLABLE.symbol symbol then
1087
          TerminalSet.union p (q())
1088 1089 1090 1091 1092 1093
        else
          p
      (* The FIRST set of the empty sequence is empty. *)
      let epsilon = TerminalSet.empty
     end)

1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104
(* ------------------------------------------------------------------------ *)

let () =
  (* If a start symbol generates the empty language or generates
     the language {epsilon}, report an error. In principle, this
     could be just a warning. However, in [Engine], in the function
     [start], it is convenient to assume that neither of these
     situations can arise. This means that at least one token must
     be read. *)
  StringSet.iter (fun symbol ->
    let nt = Nonterminal.lookup symbol in
1105
    if not (NONEMPTY.nonterminal nt) then
1106 1107
      Error.error
	(Nonterminal.positions nt)
1108
	"%s generates the empty language." (Nonterminal.print false nt);
1109
    if TerminalSet.is_empty (FIRST.nonterminal nt) then
1110 1111
      Error.error
	(Nonterminal.positions nt)
1112
	"%s generates the language {epsilon}." (Nonterminal.print false nt)
1113 1114 1115
  ) Front.grammar.start_symbols;
  (* If a nonterminal symbol generates the empty language, issue a warning. *)
  for nt = Nonterminal.start to Nonterminal.n - 1 do
1116
    if not (NONEMPTY.nonterminal nt) then
1117 1118
      Error.grammar_warning
	(Nonterminal.positions nt)
1119
	"%s generates the empty language." (Nonterminal.print false nt);
1120 1121
  done

1122
(* ------------------------------------------------------------------------ *)
1123 1124 1125 1126
(* For every nonterminal symbol [nt], compute a word of minimal length
   generated by [nt]. This analysis subsumes [NONEMPTY] and [NULLABLE].
   Indeed, [nt] produces a nonempty language if only if the minimal length is
   finite; [nt] is nullable if only if the minimal length is zero. *)
1127

1128 1129 1130 1131
(* This analysis is in principle more costly than the [NONEMPTY] and
   [NULLABLE], so it is performed only on demand. In practice, it seems
   to be very cheap: its cost is not measurable for any of the grammars
   in our benchmark suite. *)
1132 1133 1134 1135

module MINIMAL =
  GenericAnalysis
    (struct
1136 1137 1138 1139 1140
      include CompletedNatWitness
      type property = Terminal.t t
     end)
    (struct
      open CompletedNatWitness
1141
      (* A terminal symbol has length 1. *)
1142
      let terminal = singleton
1143 1144 1145 1146 1147
      (* The length of an alternative is the minimum length of any branch. *)
      let disjunction = min_lazy
      (* The length of a sequence is the sum of the lengths of the members. *)
      let conjunction _ = add_lazy
      (* The epsilon sequence has length 0. *)
1148
      let epsilon = epsilon
1149 1150
     end)

1151 1152 1153 1154 1155
(* ------------------------------------------------------------------------ *)
(* Dump the analysis results. *)

let () =
  Error.logG 2 (fun f ->
1156
    for nt = Nonterminal.start to Nonterminal.n - 1 do
1157 1158
      Printf.fprintf f "nullable(%s) = %b\n"
	(Nonterminal.print false nt)
1159
	(NULLABLE.nonterminal nt)
1160
    done;
1161
    for nt = Nonterminal.start to Nonterminal.n - 1 do
1162 1163
      Printf.fprintf f "first(%s) = %s\n"
	(Nonterminal.print false nt)
1164
	(TerminalSet.print (FIRST.nonterminal nt))
1165 1166 1167 1168
    done;
    for nt = Nonterminal.start to Nonterminal.n - 1 do
      Printf.fprintf f "minimal(%s) = %s\n"
	(Nonterminal.print false nt)
1169
	(CompletedNatWitness.print Terminal.print (MINIMAL.nonterminal nt))
1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180
    done
  )

let () =
  Time.tick "Analysis of the grammar"

(* ------------------------------------------------------------------------ *)
(* Compute FOLLOW sets. Unnecessary for us, but requested by a user. Also,
   this is useful for the SLR(1) test. Thus, we perform this analysis only
   on demand. *)

1181 1182 1183
(* The computation of the symbolic FOLLOW sets follows exactly the same
   pattern. We share code and parameterize this computation over a module [P],
   just like the little equation solver above. *)
1184

1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195
module FOLLOW (P : sig
  include Fix.PROPERTY
  val union: property -> property -> property
  val terminal: Terminal.t -> property
  val first: Production.index -> int -> property
end) = struct

  module S = Solve(P)
  open S

  (* First pass. Build a system of equations. *)
1196

1197
  let follow : equations =
1198
    Array.make Nonterminal.n (EConstant P.bottom)
1199

1200
  (* Iterate over all start symbols. *)
1201 1202 1203 1204 1205 1206 1207 1208 1209 1210
  let () =
    let sharp = EConstant (P.terminal Terminal.sharp) in
    for nt = 0 to Nonterminal.start - 1 do
      assert (Nonterminal.is_start nt);
      (* Add # to FOLLOW(nt). *)
      follow.(nt) <- EUnion (sharp, follow.(nt))
    done
    (* We need to do this explicitly because our start productions are
       of the form S' -> S, not S' -> S #, so # will not automatically
       appear into FOLLOW(S) when the start productions are examined. *)
1211

1212
  (* Iterate over all productions. *)
1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231
  let () =
    Array.iteri (fun prod (nt1, rhs) ->
      (* Iterate over all nonterminal symbols [nt2] in the right-hand side. *)
      Array.iteri (fun i symbol ->
        match symbol with
        | Symbol.T _ ->
            ()
        | Symbol.N nt2 ->
            let nullable = NULLABLE.production prod (i+1)
            and first = P.first prod (i+1) in
            (* The FIRST set of the remainder of the right-hand side
               contributes to the FOLLOW set of [nt2]. *)
            follow.(nt2) <- EUnion (EConstant first, follow.(nt2));
            (* If the remainder of the right-hand side is nullable,
               FOLLOW(nt1) contributes to FOLLOW(nt2). *)
            if nullable then
              follow.(nt2) <- EUnion (EVar nt1, follow.(nt2))
      ) rhs
    ) Production.table
1232

1233
  (* Second pass. Solve the equations (on demand). *)
1234

1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248
  let follow : Nonterminal.t -> P.property =
    solve follow

end

(* Use the above functor to obtain the standard (concrete) FOLLOW sets. *)

let follow : Nonterminal.t -> TerminalSet.t =
  let module F = FOLLOW(struct
    include TerminalSet
    let terminal = singleton
    let first = FIRST.production
  end) in
  F.follow
1249 1250 1251 1252 1253

(* At log level 2, display the FOLLOW sets. *)

let () =
  Error.logG 2 (fun f ->
1254
    for nt = Nonterminal.start to Nonterminal.n - 1 do
1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272
      Printf.fprintf f "follow(%s) = %s\n"
	(Nonterminal.print false nt)
	(TerminalSet.print (follow nt))
    done
  )

(* Compute FOLLOW sets for the terminal symbols as well. Again, unnecessary
   for us, but requested by a user. This is done in a single pass over the
   grammar -- no new fixpoint computation is required. *)

let tfollow : TerminalSet.t array Lazy.t =
  lazy (

    let tfollow =
      Array.make Terminal.n TerminalSet.empty
    in

    (* Iterate over all productions. *)
1273
    Array.iteri (fun prod (nt1, rhs) ->
1274 1275 1276 1277 1278 1279
      (* Iterate over all terminal symbols [t2] in the right-hand side. *)
      Array.iteri (fun i symbol ->
	match symbol with
	| Symbol.N _ ->
	    ()
	| Symbol.T t2 ->
1280 1281
            let nullable = NULLABLE.production prod (i+1)
            and first = FIRST.production prod (i+1) in
1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311
	    (* The FIRST set of the remainder of the right-hand side
	       contributes to the FOLLOW set of [t2]. *)
	    tfollow.(t2) <- TerminalSet.union first tfollow.(t2);
	    (* If the remainder of the right-hand side is nullable,
	       FOLLOW(nt1) contributes to FOLLOW(t2). *)
	    if nullable then
	      tfollow.(t2) <- TerminalSet.union (follow nt1) tfollow.(t2)
      ) rhs
    ) Production.table;

    tfollow

  )

(* Define another accessor. *)

let tfollow t =
  (Lazy.force tfollow).(t)

(* At log level 3, display the FOLLOW sets for terminal symbols. *)

let () =
  Error.logG 3 (fun f ->
    for t = 0 to Terminal.n - 1 do
      Printf.fprintf f "follow(%s) = %s\n"
	(Terminal.print t)
	(TerminalSet.print (tfollow t))
    done
  )

1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359
(* ------------------------------------------------------------------------ *)
(* Compute symbolic FIRST and FOLLOW sets. *)

(* The symbolic FIRST set of the word determined by [prod/i] is defined
   (and computed) as follows. *)

let sfirst prod i =
  let rhs = Production.rhs prod in
  let n = Array.length rhs in
  let rec loop i =
    if i = n then
      (* If the word [prod/i] is empty, the set is empty. *)
      SymbolSet.empty
    else
      let sym = rhs.(i) in
      (* If the word [prod/i] begins with a symbol [sym], then [sym]
         itself is part of the symbolic FIRST set, unconditionally. *)
      SymbolSet.union
        (SymbolSet.singleton sym)
        (* Furthermore, if [sym] is nullable, then the symbolic
           FIRST set of the sub-word [prod/i+1] contributes, too. *)
        (if NULLABLE.symbol sym then loop (i + 1) else SymbolSet.empty)
  in
  loop i

(* The symbolic FOLLOW sets are computed just like the FOLLOW sets,
   except we use a symbolic FIRST set instead of a standard FIRST
   set. *)

let sfollow : Nonterminal.t -> SymbolSet.t =
  let module F = FOLLOW(struct
    include SymbolSet
    let terminal t = SymbolSet.singleton (Symbol.T t)
    let first = sfirst
  end) in
  F.follow

(* At log level 3, display the symbolic FOLLOW sets. *)

let () =
  Error.logG 3 (fun f ->
    for nt = Nonterminal.start to Nonterminal.n - 1 do
      Printf.fprintf f "sfollow(%s) = %s\n"
	(Nonterminal.print false nt)
	(SymbolSet.print (sfollow nt))
    done
  )

1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387
(* ------------------------------------------------------------------------ *)
(* Provide explanations about FIRST sets. *)

(* The idea is to explain why a certain token appears in the FIRST set
   for a certain sequence of symbols. Such an explanation involves
   basic assertions of the form (i) symbol N is nullable and (ii) the
   token appears in the FIRST set for symbol N. We choose to take
   these basic facts for granted, instead of recursively explaining
   them, so as to keep explanations short. *)

(* We first produce an explanation in abstract syntax, then
   convert it to a human-readable string. *)

type explanation =
  | EObvious                                 (* sequence begins with desired token *)
  | EFirst of Terminal.t * Nonterminal.t     (* sequence begins with a nonterminal that produces desired token *)
  | ENullable of Symbol.t list * explanation (* sequence begins with a list of nullable symbols and ... *)

let explain (tok : Terminal.t) (rhs : Symbol.t array) (i : int) =
  let length = Array.length rhs in
  let rec loop i =
    assert (i < length);
    let symbol = rhs.(i) in
    match symbol with
    | Symbol.T tok' ->
	assert (Terminal.equal tok tok');
	EObvious
    | Symbol.N nt ->
1388
	if TerminalSet.mem tok (FIRST.nonterminal nt) then
1389 1390
	  EFirst (tok, nt)
	else begin
1391
	  assert (NULLABLE.nonterminal nt);
1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419
	  match loop (i + 1) with
	  | ENullable (symbols, e) ->
	      ENullable (symbol :: symbols, e)
	  | e ->
	      ENullable ([ symbol ], e)
	end
  in
  loop i

let rec convert = function
  | EObvious ->
      ""
  | EFirst (tok, nt) ->
      Printf.sprintf "%s can begin with %s"
	(Nonterminal.print false nt)
	(Terminal.print tok)
  | ENullable (symbols, e) ->
      let e = convert e in
      Printf.sprintf "%scan vanish%s%s"
	(Symbol.printl symbols)
	(if e = "" then "" else " and ")
	e

(* ------------------------------------------------------------------------ *)
(* Package the analysis results. *)

module Analysis = struct

1420
  let nullable = NULLABLE.nonterminal
1421

1422
  let first = FIRST.nonterminal
POTTIER Francois's avatar
POTTIER Francois committed
1423

1424 1425
  (* An initial definition of [nullable_first_prod]. *)

1426
  let nullable_first_prod prod i =
1427 1428
    NULLABLE.production prod i,
    FIRST.production prod i
1429

1430 1431 1432 1433 1434 1435 1436 1437 1438 1439
  (* A memoised version, so as to avoid recomputing along a production's
     right-hand side. *)

  let nullable_first_prod =
    Misc.tabulate Production.n (fun prod ->
      Misc.tabulate (Production.length prod + 1) (fun i ->
        nullable_first_prod prod i
      )
    )

1440
  let first_prod_lookahead prod i z =
1441 1442
    let nullable, first = nullable_first_prod prod i in
    if nullable then
1443 1444 1445 1446
      TerminalSet.add z first
    else
      first

1447 1448 1449 1450 1451
  let explain_first_rhs (tok : Terminal.t) (rhs : Symbol.t array) (i : int) =
    convert (explain tok rhs i)

  let follow = follow

POTTIER Francois's avatar
POTTIER Francois committed
1452
  let minimal_symbol = MINIMAL.symbol
POTTIER Francois's avatar
POTTIER Francois committed
1453 1454
  let minimal_prod = MINIMAL.production

1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485
end

(* ------------------------------------------------------------------------ *)
(* Conflict resolution via precedences. *)

module Precedence = struct

  type choice =
    | ChooseShift
    | ChooseReduce
    | ChooseNeither
    | DontKnow

  type order = Lt | Gt | Eq | Ic

  let precedence_order p1 p2 = 
    match p1, p2 with
      |	UndefinedPrecedence, _
      | _, UndefinedPrecedence -> 
	  Ic
      | PrecedenceLevel (m1, l1, _, _), PrecedenceLevel (m2, l2, _, _) ->
	  if not (Mark.same m1 m2) then
	    Ic
	  else
	    if l1 > l2 then 
	      Gt 
	    else if l1 < l2 then 
	      Lt
	    else 
	      Eq

1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498
  let production_order p1 p2 =
    match p1, p2 with
      | ProductionLevel (m1, l1), ProductionLevel (m2, l2) ->
	  if not (Mark.same m1 m2) then
	    Ic
	  else
	    if l1 > l2 then 
	      Gt 
	    else if l1 < l2 then 
	      Lt
	    else 
	      Eq

1499 1500
  let shift_reduce tok prod =
    let fact1, tokp  = Terminal.precedence_level tok
1501
    and fact2, prodp = Production.precedence prod in
1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539
    match precedence_order tokp prodp with
   
      (* Our information is inconclusive. Drop [fact1] and [fact2],
	 that is, do not record that this information was useful. *)

    | Ic ->
	DontKnow

      (* Our information is useful. Record that fact by evaluating
	 [fact1] and [fact2]. *)

    | (Eq | Lt | Gt) as c ->
	Lazy.force fact1;
	Lazy.force fact2;
	match c with

	| Ic ->
	    assert false (* already dispatched *)

	| Eq -> 
	    begin
	      match Terminal.associativity tok with
	      | LeftAssoc  -> ChooseReduce
	      | RightAssoc -> ChooseShift
	      | NonAssoc   -> ChooseNeither
	      | _          -> assert false
			      (* If [tok]'s precedence level is defined, then
				 its associativity must be defined as well. *)
	    end

	| Lt ->
	    ChooseReduce

	| Gt ->