MAJ terminée. Nous sommes passés en version 14.6.2 . Pour consulter les "releases notes" associées c'est ici :

https://about.gitlab.com/releases/2022/01/11/security-release-gitlab-14-6-2-released/
https://about.gitlab.com/releases/2022/01/04/gitlab-14-6-1-released/

IncrementalEngine.ml 19.3 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
(******************************************************************************)
(*                                                                            *)
(*                                   Menhir                                   *)
(*                                                                            *)
(*                       François Pottier, Inria Paris                        *)
(*              Yann Régis-Gianas, PPS, Université Paris Diderot              *)
(*                                                                            *)
(*  Copyright Inria. All rights reserved. This file is distributed under the  *)
(*  terms of the GNU Library General Public License version 2, with a         *)
(*  special exception on linking, as described in the file LICENSE.           *)
(*                                                                            *)
(******************************************************************************)

14
15
type position = Lexing.position

16
17
open General

18
19
20
21
22
23
24
25
26
(* This signature describes the incremental LR engine. *)

(* In this mode, the user controls the lexer, and the parser suspends
   itself when it needs to read a new token. *)

module type INCREMENTAL_ENGINE = sig

  type token

27
28
29
30
31
32
  (* A value of type [production] is (an index for) a production. The start
     productions (which do not exist in an \mly file, but are constructed by
     Menhir internally) are not part of this type. *)

  type production

33
34
  (* The type ['a checkpoint] represents an intermediate or final state of the
     parser. An intermediate checkpoint is a suspension: it records the parser's
35
36
37
38
     current state, and allows parsing to be resumed. The parameter ['a] is
     the type of the semantic value that will eventually be produced if the
     parser succeeds. *)

39
  (* [Accepted] and [Rejected] are final checkpoints. [Accepted] carries a
40
41
     semantic value. *)

42
  (* [InputNeeded] is an intermediate checkpoint. It means that the parser wishes
43
44
     to read one token before continuing. *)

45
  (* [Shifting] is an intermediate checkpoint. It means that the parser is taking
46
47
48
49
50
     a shift transition. It exposes the state of the parser before and after
     the transition. The Boolean parameter tells whether the parser intends to
     request a new token after this transition. (It always does, except when
     it is about to accept.) *)

51
  (* [AboutToReduce] is an intermediate checkpoint. It means that the parser is
52
53
     about to perform a reduction step. It exposes the parser's current
     state as well as the production that is about to be reduced. *)
54

55
  (* [HandlingError] is an intermediate checkpoint. It means that the parser has
56
     detected an error and is currently handling it, in several steps. *)
57

58
59
60
61
62
63
64
65
66
67
68
69
70
  (* A value of type ['a env] represents a configuration of the automaton:
     current state, stack, lookahead token, etc. The parameter ['a] is the
     type of the semantic value that will eventually be produced if the parser
     succeeds. *)

  (* In normal operation, the parser works with checkpoints: see the functions
     [offer] and [resume]. However, it is also possible to work directly with
     environments (see the functions [pop], [force_reduction], and [feed]) and
     to reconstruct a checkpoint out of an environment (see [input_needed]).
     This is considered advanced functionality; its purpose is to allow error
     recovery strategies to be programmed by the user. *)

  type 'a env
71

72
  type 'a checkpoint = private
73
74
75
76
    | InputNeeded of 'a env
    | Shifting of 'a env * 'a env * bool
    | AboutToReduce of 'a env * production
    | HandlingError of 'a env
77
78
79
80
    | Accepted of 'a
    | Rejected

  (* [offer] allows the user to resume the parser after it has suspended
81
82
     itself with a checkpoint of the form [InputNeeded env]. [offer] expects the
     old checkpoint as well as a new token and produces a new checkpoint. It does not
83
     raise any exception. *)
84
85

  val offer:
86
    'a checkpoint ->
87
    token * position * position ->
88
    'a checkpoint
89

90
  (* [resume] allows the user to resume the parser after it has suspended
91
92
93
     itself with a checkpoint of the form [AboutToReduce (env, prod)] or
     [HandlingError env]. [resume] expects the old checkpoint and produces a new
     checkpoint. It does not raise any exception. *)
94

95
  val resume:
96
97
    'a checkpoint ->
    'a checkpoint
98

99
100
101
102
  (* A token supplier is a function of no arguments which delivers a new token
     (together with its start and end positions) every time it is called. *)

  type supplier =
103
    unit -> token * position * position
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119

  (* A pair of a lexer and a lexing buffer can be easily turned into a supplier. *)

  val lexer_lexbuf_to_supplier:
    (Lexing.lexbuf -> token) ->
    Lexing.lexbuf ->
    supplier

  (* The functions [offer] and [resume] are sufficient to write a parser loop.
     One can imagine many variations (which is why we expose these functions
     in the first place!). Here, we expose a few variations of the main loop,
     ready for use. *)

  (* [loop supplier checkpoint] begins parsing from [checkpoint], reading
     tokens from [supplier]. It continues parsing until it reaches a
     checkpoint of the form [Accepted v] or [Rejected]. In the former case, it
POTTIER Francois's avatar
POTTIER Francois committed
120
     returns [v]. In the latter case, it raises the exception [Error]. *)
121
122
123
124
125
126
127

  val loop: supplier -> 'a checkpoint -> 'a

  (* [loop_handle succeed fail supplier checkpoint] begins parsing from
     [checkpoint], reading tokens from [supplier]. It continues parsing until
     it reaches a checkpoint of the form [Accepted v] or [HandlingError env]
     (or [Rejected], but that should not happen, as [HandlingError _] will be
POTTIER Francois's avatar
POTTIER Francois committed
128
129
     observed first). In the former case, it calls [succeed v]. In the latter
     case, it calls [fail] with this checkpoint. It cannot raise [Error].
130
131
132
133

     This means that Menhir's traditional error-handling procedure (which pops
     the stack until a state that can act on the [error] token is found) does
     not get a chance to run. Instead, the user can implement her own error
POTTIER Francois's avatar
POTTIER Francois committed
134
     handling code, in the [fail] continuation. *)
135
136
137
138
139

  val loop_handle:
    ('a -> 'answer) ->
    ('a checkpoint -> 'answer) ->
    supplier -> 'a checkpoint -> 'answer
140

POTTIER Francois's avatar
POTTIER Francois committed
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
  (* [loop_handle_undo] is analogous to [loop_handle], except it passes a pair
     of checkpoints to the failure continuation.

     The first (and oldest) checkpoint is the last [InputNeeded] checkpoint that
     was encountered before the error was detected. The second (and newest)
     checkpoint is where the error was detected, as in [loop_handle]. Going back
     to the first checkpoint can be thought of as undoing any reductions that
     were performed after seeing the problematic token. (These reductions must
     be default reductions or spurious reductions.)

     [loop_handle_undo] must initially be applied to an [InputNeeded] checkpoint.
     The parser's initial checkpoints satisfy this constraint. *)

  val loop_handle_undo:
    ('a -> 'answer) ->
    ('a checkpoint -> 'a checkpoint -> 'answer) ->
    supplier -> 'a checkpoint -> 'answer

159
160
161
162
163
164
165
  (* [shifts checkpoint] assumes that [checkpoint] has been obtained by
     submitting a token to the parser. It runs the parser from [checkpoint],
     through an arbitrary number of reductions, until the parser either
     accepts this token (i.e., shifts) or rejects it (i.e., signals an error).
     If the parser decides to shift, then [Some env] is returned, where [env]
     is the parser's state just before shifting. Otherwise, [None] is
     returned. *)
POTTIER Francois's avatar
POTTIER Francois committed
166
167
168
169

  (* It is desirable that the semantic actions be side-effect free, or that
     their side-effects be harmless (replayable). *)

170
  val shifts: 'a checkpoint -> 'a env option
POTTIER Francois's avatar
POTTIER Francois committed
171

172
173
  (* The function [acceptable] allows testing, after an error has been
     detected, which tokens would have been accepted at this point. It is
POTTIER Francois's avatar
POTTIER Francois committed
174
175
     implemented using [shifts]. Its argument should be an [InputNeeded]
     checkpoint. *)
POTTIER Francois's avatar
POTTIER Francois committed
176
177
178
179
180
181
182
183
184
185
186
187

  (* For completeness, one must undo any spurious reductions before carrying out
     this test -- that is, one must apply [acceptable] to the FIRST checkpoint
     that is passed by [loop_handle_undo] to its failure continuation. *)

  (* This test causes some semantic actions to be run! The semantic actions
     should be side-effect free, or their side-effects should be harmless. *)

  (* The position [pos] is used as the start and end positions of the
     hypothetical token, and may be picked up by the semantic actions. We
     suggest using the position where the error was detected. *)

188
  val acceptable: 'a checkpoint -> token -> position -> bool
POTTIER Francois's avatar
POTTIER Francois committed
189

190
191
192
193
194
  (* [pop env] returns a new environment, where the parser's top stack cell
     has been popped off. (If the stack is empty, [None] is returned.) This
     amounts to pretending that the (terminal or nonterminal) symbol that
     corresponds to this stack cell has not been read. *)

195
  val pop: 'a env -> 'a env option
196

POTTIER Francois's avatar
POTTIER Francois committed
197
198
199
200
201
202
  (* [force_reduction prod env] should be called only if in the state [env]
     the parser is capable of reducing the production [prod]. If this
     condition is satisfied, then this production is reduced, which means that
     its semantic action is executed (this can have side effects!) and the
     automaton makes a goto (nonterminal) transition. If this condition is not
     satisfied, [Invalid_argument _] is raised. *)
203

204
  val force_reduction: production -> 'a env -> 'a env
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219

  (* [input_needed env] returns [InputNeeded env]. That is, out of an [env]
     that might have been obtained via a series of calls to the functions
     [pop], [force_reduction], [feed], etc., it produces a checkpoint, which
     can be used to resume normal parsing, by supplying this checkpoint as an
     argument to [offer]. *)

  (* This function should be used with some care. It could "mess up the
     lookahead" in the sense that it allows parsing to resume in an arbitrary
     state [s] with an arbitrary lookahead symbol [t], even though Menhir's
     reachability analysis (menhir --list-errors) might well think that it is
     impossible to reach this particular configuration. If one is using
     Menhir's new error reporting facility, this could cause the parser to
     reach an error state for which no error message has been prepared. *)

220
  val input_needed: 'a env -> 'a checkpoint
221

222
223
224
225
226
227
  (* The abstract type ['a lr1state] describes the non-initial states of the
     LR(1) automaton. The index ['a] represents the type of the semantic value
     associated with this state's incoming symbol. *)

  type 'a lr1state

228
229
230
231
  (* The states of the LR(1) automaton are numbered (from 0 and up). *)

  val number: _ lr1state -> int

232
233
234
235
236
237
238
  (* Productions are numbered. *)

  (* [find_production i] requires the index [i] to be valid. Use with care. *)

  val production_index: production -> int
  val find_production: int -> production

239
240
241
  (* An element is a pair of a non-initial state [s] and a semantic value [v]
     associated with the incoming symbol of this state. The idea is, the value
     [v] was pushed onto the stack just before the state [s] was entered. Thus,
242
     for some type ['a], the state [s] has type ['a lr1state] and the value [v]
243
244
245
     has type ['a]. In other words, the type [element] is an existential type. *)

  type element =
246
    | Element: 'a lr1state * 'a * position * position -> element
247
248

  (* The parser's stack is (or, more precisely, can be viewed as) a stream of
POTTIER Francois's avatar
POTTIER Francois committed
249
     elements. The type [stream] is defined by the module [General]. *)
250

251
252
253
  (* As of 2017/03/31, the types [stream] and [stack] and the function [stack]
     are DEPRECATED. They might be removed in the future. An alternative way
     of inspecting the stack is via the functions [top] and [pop]. *)
254
255

  type stack = (* DEPRECATED *)
256
257
    element stream

258
259
260
261
  (* This is the parser's stack, a stream of elements. This stream is empty if
     the parser is in an initial state; otherwise, it is non-empty.  The LR(1)
     automaton's current state is the one found in the top element of the
     stack. *)
262

263
264
  val stack: 'a env -> stack (* DEPRECATED *)

POTTIER Francois's avatar
POTTIER Francois committed
265
266
267
268
  (* [top env] returns the parser's top stack element. The state contained in
     this stack element is the current state of the automaton. If the stack is
     empty, [None] is returned. In that case, the current state of the
     automaton must be an initial state. *)
269
270

  val top: 'a env -> element option
271

POTTIER Francois's avatar
POTTIER Francois committed
272
273
  (* [pop_many i env] pops [i] cells off the automaton's stack. This is done
     via [i] successive invocations of [pop]. Thus, [pop_many 1] is [pop]. The
274
275
     index [i] must be nonnegative. The time complexity is O(i). *)

276
  val pop_many: int -> 'a env -> 'a env option
277
278
279
280
281
282
283
284

  (* [get i env] returns the parser's [i]-th stack cell. The index [i] is
     0-based: thus, [get 0] is [top]. If [i] is greater than or equal to the
     number of elements in the stack, [None] is returned. The time complexity
     is O(i). *)

  val get: int -> 'a env -> element option

285
286
287
288
289
290
291
  (* [current_state_number env] returns (the integer number of) the automaton's
     current state. This works even if the automaton's stack is empty, in which
     case the current state is an initial state. This number can be used as an
     argument to a [message] function that was generated by [menhir
     --compile-errors]. *)

  val current_state_number: 'a env -> int
POTTIER Francois's avatar
POTTIER Francois committed
292

293
  (* [equal env1 env2] tells whether the parser configurations [env1] and
294
295
296
297
298
299
300
     [env2] are equal in the sense that the automaton's current state is the
     same in [env1] and [env2] and the stack is *physically* the same in
     [env1] and [env2]. If [equal env1 env2] is [true], then the list of stack
     elements, as observed via [pop] and [top], must be the same in [env1] and
     [env2]. Also, if [equal env1 env2], then the checkpoints [input_needed
     env1] and [input_needed env2] are equivalent. The function [equal] has
     time complexity O(1). *)
301
302
303

  val equal: 'a env -> 'a env -> bool

304
305
306
  (* These are the start and end positions of the current lookahead token. If
     invoked in an initial state, this function returns a pair of twice the
     initial position. *)
307

308
  val positions: 'a env -> position * position
309

310
311
312
313
  (* When applied to an environment taken from a checkpoint of the form
     [AboutToReduce (env, prod)], the function [env_has_default_reduction]
     tells whether the reduction that is about to take place is a default
     reduction. *)
314

315
  val env_has_default_reduction: 'a env -> bool
316

317
318
319
320
321
  (* [state_has_default_reduction s] tells whether the state [s] has a default
     reduction. This includes the case where [s] is an accepting state. *)

  val state_has_default_reduction: _ lr1state -> bool

322
end
323

324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
(* This signature is a fragment of the inspection API that is made available
   to the user when [--inspection] is used. This fragment contains type
   definitions for symbols. *)

module type SYMBOLS = sig

  (* The type ['a terminal] represents a terminal symbol. The type ['a
     nonterminal] represents a nonterminal symbol. In both cases, the index
     ['a] represents the type of the semantic values associated with this
     symbol. The concrete definitions of these types are generated. *)

  type 'a terminal
  type 'a nonterminal

  (* The type ['a symbol] represents a terminal or nonterminal symbol. It is
     the disjoint union of the types ['a terminal] and ['a nonterminal]. *)

  type 'a symbol =
    | T : 'a terminal -> 'a symbol
    | N : 'a nonterminal -> 'a symbol

  (* The type [xsymbol] is an existentially quantified version of the type
     ['a symbol]. This type is useful in situations where the index ['a]
     is not statically known. *)

POTTIER Francois's avatar
POTTIER Francois committed
349
  type xsymbol =
350
351
352
353
    | X : 'a symbol -> xsymbol

end

354
355
(* This signature describes the inspection API that is made available to the
   user when [--inspection] is used. *)
356
357
358

module type INSPECTION = sig

359
360
361
362
  (* The types of symbols are described above. *)

  include SYMBOLS

363
364
  (* The type ['a lr1state] is meant to be the same as in [INCREMENTAL_ENGINE]. *)

365
  type 'a lr1state
366

367
368
369
370
  (* The type [production] is meant to be the same as in [INCREMENTAL_ENGINE].
     It represents a production of the grammar. A production can be examined
     via the functions [lhs] and [rhs] below. *)

371
372
  type production

373
374
375
376
  (* An LR(0) item is a pair of a production [prod] and a valid index [i] into
     this production. That is, if the length of [rhs prod] is [n], then [i] is
     comprised between 0 and [n], inclusive. *)

377
  type item =
378
379
      production * int

380
381
382
383
384
385
386
387
  (* Ordering functions. *)

  val compare_terminals: _ terminal -> _ terminal -> int
  val compare_nonterminals: _ nonterminal -> _ nonterminal -> int
  val compare_symbols: xsymbol -> xsymbol -> int
  val compare_productions: production -> production -> int
  val compare_items: item -> item -> int

388
389
390
391
392
393
  (* [incoming_symbol s] is the incoming symbol of the state [s], that is,
     the symbol that the parser must recognize before (has recognized when)
     it enters the state [s]. This function gives access to the semantic
     value [v] stored in a stack element [Element (s, v, _, _)]. Indeed,
     by case analysis on the symbol [incoming_symbol s], one discovers the
     type ['a] of the value [v]. *)
394

POTTIER Francois's avatar
POTTIER Francois committed
395
  val incoming_symbol: 'a lr1state -> 'a symbol
396

POTTIER Francois's avatar
POTTIER Francois committed
397
398
399
400
401
402
  (* [items s] is the set of the LR(0) items in the LR(0) core of the LR(1)
     state [s]. This set is not epsilon-closed. This set is presented as a
     list, in an arbitrary order. *)

  val items: _ lr1state -> item list

403
404
405
  (* [lhs prod] is the left-hand side of the production [prod]. This is
     always a non-terminal symbol. *)

406
407
  val lhs: production -> xsymbol

408
409
410
  (* [rhs prod] is the right-hand side of the production [prod]. This is
     a (possibly empty) sequence of (terminal or nonterminal) symbols. *)

411
412
  val rhs: production -> xsymbol list

413
414
415
416
  (* [nullable nt] tells whether the non-terminal symbol [nt] is nullable.
     That is, it is true if and only if this symbol produces the empty
     word [epsilon]. *)

417
  val nullable: _ nonterminal -> bool
418

419
420
421
422
  (* [first nt t] tells whether the FIRST set of the nonterminal symbol [nt]
     contains the terminal symbol [t]. That is, it is true if and only if
     [nt] produces a word that begins with [t]. *)

423
424
425
426
427
428
  val first: _ nonterminal -> _ terminal -> bool

  (* [xfirst] is analogous to [first], but expects a first argument of type
     [xsymbol] instead of [_ terminal]. *)

  val xfirst: xsymbol -> _ terminal -> bool
429

430
431
432
433
434
435
436
  (* [foreach_terminal] enumerates the terminal symbols, including [error].
     [foreach_terminal_but_error] enumerates the terminal symbols, excluding
     [error]. *)

  val foreach_terminal:           (xsymbol -> 'a -> 'a) -> 'a -> 'a
  val foreach_terminal_but_error: (xsymbol -> 'a -> 'a) -> 'a -> 'a

437
438
  (* The type [env] is meant to be the same as in [INCREMENTAL_ENGINE]. *)

439
  type 'a env
440
441
442
443
444
445
446
447
448

  (* [feed symbol startp semv endp env] forces the parser to consume the
     (terminal or nonterminal) symbol [symbol], accompanied with the semantic
     value [semv] and with the positions [startp] and [endp]. Thus, the
     automaton makes a transition, and reaches a new state. The stack grows by
     one cell. This operation is permitted only if the current state (as
     determined by [env]) has an outgoing transition labeled with [symbol].
     Otherwise, [Invalid_argument _] is raised. *)

449
  val feed: 'a symbol -> position -> 'a -> position -> 'b env -> 'b env
450

451
452
end

453
454
455
456
457
458
459
460
461
(* This signature combines the incremental API and the inspection API. *)

module type EVERYTHING = sig

  include INCREMENTAL_ENGINE

  include INSPECTION
    with type 'a lr1state := 'a lr1state
    with type production := production
462
    with type 'a env := 'a env
463
464

end