parse.py 119 KB
Newer Older
1
# parse.py - parser combinators for DHParser
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
#
# Copyright 2016  by Eckhart Arnold (arnold@badw.de)
#                 Bavarian Academy of Sciences an Humanities (badw.de)
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.  See the License for the specific language governing
# permissions and limitations under the License.
Eckhart Arnold's avatar
Eckhart Arnold committed
17

18
19

"""
20
Module ``parse`` contains the python classes and functions for
21
22
DHParser's packrat-parser. It's central class is the
``Grammar``-class, which is the base class for any concrete
23
24
25
26
27
28
29
30
31
Grammar. Grammar-objects are callable and parsing is done by
calling a Grammar-object with a source text as argument.

The different parsing functions are callable descendants of class
``Parser``. Usually, they are organized in a tree and defined
within the namespace of a grammar-class. See ``ebnf.EBNFGrammar``
for an example.
"""

32

33
from collections import defaultdict
34
import copy
35
from typing import Callable, cast, List, Tuple, Set, Container, Dict, \
36
    DefaultDict, Union, Optional, Any
37

eckhart's avatar
eckhart committed
38
from DHParser.configuration import get_config_value
39
from DHParser.error import Error, linebreaks, line_col
40
from DHParser.log import HistoryRecord
41
from DHParser.preprocess import BEGIN_TOKEN, END_TOKEN, RX_TOKEN_NAME
42
from DHParser.stringview import StringView, EMPTY_STRING_VIEW
43
from DHParser.syntaxtree import Node, FrozenNode, RootNode, WHITESPACE_PTYPE, \
44
    TOKEN_PTYPE, ZOMBIE_TAG, EMPTY_NODE, ResultType
45
from DHParser.toolkit import sane_parser_name, escape_control_characters, re, cython, \
46
    RX_NEVER_MATCH, RxPatternType
47

48

49
__all__ = ('ParserError',
eckhart's avatar
eckhart committed
50
51
52
           'ApplyFunc',
           'FlagFunc',
           'ParseFunc',
53
           'Parser',
54
           'UnknownParserError',
55
56
           'GrammarErrorType',
           'GrammarError',
57
58
           'Grammar',
           'PreprocessorToken',
59
           'Token',
60
           'DropToken',
61
           'RegExp',
62
63
           'RE',
           'TKN',
64
           'Whitespace',
65
           'DropRegExp',
66
           'mixin_comment',
Eckhart Arnold's avatar
Eckhart Arnold committed
67
           'mixin_noempty',
68
           'MetaParser',
eckhart's avatar
eckhart committed
69
70
           'UnaryParser',
           'NaryParser',
71
           'Drop',
72
73
74
75
76
77
78
79
80
           'Synonym',
           'Option',
           'ZeroOrMore',
           'OneOrMore',
           'Series',
           'Alternative',
           'AllOf',
           'SomeOf',
           'Unordered',
eckhart's avatar
eckhart committed
81
           'Required',
82
83
84
85
86
87
88
89
90
91
           'Lookahead',
           'NegativeLookahead',
           'Lookbehind',
           'NegativeLookbehind',
           'last_value',
           'counterpart',
           'accumulate',
           'Capture',
           'Retrieve',
           'Pop',
92
           'Forward')
93
94
95
96


########################################################################
#
97
# ParserError class
98
99
100
101
#
########################################################################


Eckhart Arnold's avatar
Eckhart Arnold committed
102
103
104
class ParserError(Exception):
    """
    A `ParserError` is thrown for those parser errors that allow the
105
    controlled re-entrance of the parsing process after the error occurred.
Eckhart Arnold's avatar
Eckhart Arnold committed
106
    If a reentry-rule has been configured for the parser where the error
107
    occurred, the parser guard can resume the parsing process.
Eckhart Arnold's avatar
Eckhart Arnold committed
108
109

    Currently, the only case when a `ParserError` is thrown (and not some
110
111
    different kind of error like `UnknownParserError`) is when a `Series`-
    or `AllOf`-parser detects a missing mandatory element.
Eckhart Arnold's avatar
Eckhart Arnold committed
112
    """
113
114
115
116
    def __init__(self, node: Node, rest: StringView, error: Optional[Error], first_throw: bool):
        self.node = node   # type: Node
        self.rest = rest   # type: StringView
        self.error = error # type: Optional[Error]
117
        self.first_throw = first_throw  # type: bool
Eckhart Arnold's avatar
Eckhart Arnold committed
118

119
    def __str__(self):
120
        return "%i: %s    %s" % (self.node.pos, str(self.rest[:25]), repr(self.node))
121

Eckhart Arnold's avatar
Eckhart Arnold committed
122

123
ResumeList = List[RxPatternType]  # list of regular expressiones
Eckhart Arnold's avatar
Eckhart Arnold committed
124
125


eckhart's avatar
eckhart committed
126
@cython.locals(upper_limit=cython.int, closest_match=cython.int, pos=cython.int)
127
128
129
def reentry_point(rest: StringView,
                  rules: ResumeList,
                  comment_regex,
130
                  search_window: int = -1) -> int:
Eckhart Arnold's avatar
Eckhart Arnold committed
131
132
    """
    Finds the point where parsing should resume after a ParserError has been caught.
133
    The algorithm makes sure that this reentry-point does not lie inside a comment.
134
135
136
    The re-entry point is always the point after the end of the match of the regular
    expression defining the re-entry point. (Use look ahead, if you wand to define
    the re-entry point by what follows rather than by what text precedes the point.)
Eckhart Arnold's avatar
Eckhart Arnold committed
137
138
    Args:
        rest:  The rest of the parsed text or, in other words, the point where
139
140
141
142
            a ParserError was thrown.
        rules: A list of regular expressions. The rest of the text is searched for
            each of these. The closest match is the point where parsing will be
            resumed.
143
        comment_regex: A regular expression object that matches comments.
144
145
        search_window: The maximum size of the search window for finding the
            reentry-point. A value smaller or equal zero means that
Eckhart Arnold's avatar
Eckhart Arnold committed
146
    Returns:
147
148
        The integer index of the closest reentry point or -1 if no reentry-point
        was found.
Eckhart Arnold's avatar
Eckhart Arnold committed
149
    """
150
    upper_limit = len(rest) + 1
151
    closest_match = upper_limit
152
153
    comments = None  # typ: Optional[Iterator]

eckhart's avatar
eckhart committed
154
    @cython.locals(a=cython.int, b=cython.int)
155
156
157
158
159
160
161
162
163
164
165
    def next_comment() -> Tuple[int, int]:
        nonlocal rest, comments
        if comments:
            try:
                m = next(comments)
                a, b = m.span()
                return rest.index(a), rest.index(b)
            except StopIteration:
                comments = None
        return -1, -2

166
167
    # def str_search(s, start: int = 0) -> Tuple[int, int]:
    #     nonlocal rest
168
    #     return rest.find(s, start, start + search_window), len(s)
169

eckhart's avatar
eckhart committed
170
    @cython.locals(start=cython.int, end=cython.int)
171
172
    def rx_search(rx, start: int = 0) -> Tuple[int, int]:
        nonlocal rest
173
        m = rest.search(rx, start, start + search_window)
174
        if m:
175
176
            begin, end = m.span()
            return rest.index(begin), end - begin
177
178
        return -1, 0

eckhart's avatar
eckhart committed
179
    @cython.locals(a=cython.int, b=cython.int, k=cython.int, length=cython.int)
180
181
182
183
184
    def entry_point(search_func, search_rule) -> int:
        a, b = next_comment()
        k, length = search_func(search_rule)
        while a < b <= k:
            a, b = next_comment()
185
186
187
        # find next as long as start or end point of resume regex are inside a comment
        while (a < k < b) or (a < k + length < b):
            k, length = search_func(search_rule, b)
188
189
            while a < b <= k:
                a, b = next_comment()
190
        return k + length if k >= 0 else upper_limit
191

192
    # find closest match
Eckhart Arnold's avatar
Eckhart Arnold committed
193
    for rule in rules:
194
        comments = rest.finditer(comment_regex)
195
196
197
        assert not isinstance(rule, str), \
            'Strings not allowed as search rules, use a regular expression instead.'
        pos = entry_point(rx_search, rule)
198
        closest_match = min(pos, closest_match)
199

200
    # in case no rule matched return -1
201
202
203
    if closest_match == upper_limit:
        closest_match = -1
    return closest_match
Eckhart Arnold's avatar
Eckhart Arnold committed
204
205


206
207
208
209
210
211
212
########################################################################
#
# Parser base class
#
########################################################################


eckhart's avatar
eckhart committed
213
214
ApplyFunc = Callable[['Parser'], None]
FlagFunc = Callable[[ApplyFunc, Set[ApplyFunc]], bool]
215
ParseFunc = Callable[['Parser', StringView], Tuple[Optional[Node], StringView]]
eckhart's avatar
eckhart committed
216
217


218
219
220
221
def copy_parser_attrs(src: 'Parser', duplicate: 'Parser'):
    """Duplicates all parser attributes from source to dest."""
    duplicate.pname = src.pname
    duplicate.anonymous = src.anonymous
Eckhart Arnold's avatar
Eckhart Arnold committed
222
    duplicate.drop_content = src.drop_content
223
224
225
    duplicate.tag_name = src.tag_name


226
class Parser:
227
228
229
230
231
232
233
234
235
236
237
238
239
240
    """
    (Abstract) Base class for Parser combinator parsers. Any parser
    object that is actually used for parsing (i.e. no mock parsers)
    should should be derived from this class.

    Since parsers can contain other parsers (see classes UnaryOperator
    and NaryOperator) they form a cyclical directed graph. A root
    parser is a parser from which all other parsers can be reached.
    Usually, there is one root parser which serves as the starting
    point of the parsing process. When speaking of "the root parser"
    it is this root parser object that is meant.

    There are two different types of parsers:

di68kap's avatar
di68kap committed
241
    1. *Named parsers* for which a name is set in field `parser.pname`.
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
       The results produced by these parsers can later be retrieved in
       the AST by the parser name.

    2. *Anonymous parsers* where the name-field just contains the empty
       string. AST-transformation of Anonymous parsers can be hooked
       only to their class name, and not to the individual parser.

    Parser objects are callable and parsing is done by calling a parser
    object with the text to parse.

    If the parser matches it returns a tuple consisting of a node
    representing the root of the concrete syntax tree resulting from the
    match as well as the substring `text[i:]` where i is the length of
    matched text (which can be zero in the case of parsers like
    `ZeroOrMore` or `Option`). If `i > 0` then the parser has "moved
    forward".

    If the parser does not match it returns `(None, text). **Note** that
    this is not the same as an empty match `("", text)`. Any empty match
    can for example be returned by the `ZeroOrMore`-parser in case the
    contained parser is repeated zero times.

    Attributes and Properties:
265

266
267
        pname:  The parser's name or a (possibly empty) alias name in case
                of an anonymous parser.
268

269
270
271
272
273
        anonymous: A property indicating that the parser remains anynomous
                anonymous with respect to the nodes it returns. For performance
                reasons this is implemented as an object variable rather
                than a property. This property must always be equal to
                `self.tag_name[0] == ":"`.
274

275
276
277
278
        drop_content: A property (for performance reasons implemented as
                simple field) that, if set, induces the parser not to return
                the parsed content or sub-tree if it has matched but the
                dummy `EMPTY_NODE`. In effect the parsed content will be
279
280
281
                dropped from the concrete syntax tree already. Only
                anonymous (or pseudo-anonymous) parsers are allowed to
                drop content.
282

283
        tag_name: The tag_name for the nodes that are created by
284
285
                the parser. If the parser is named, this is the same as
                `pname`, otherwise it is the name of the parser's type.
286

287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
        visited:  Mapping of places this parser has already been to
                during the current parsing process onto the results the
                parser returned at the respective place. This dictionary
                is used to implement memoizing.

        recursion_counter:  Mapping of places to how often the parser
                has already been called recursively at this place. This
                is needed to implement left recursion. The number of
                calls becomes irrelevant once a resault has been memoized.

        cycle_detection:  The apply()-method uses this variable to make
                sure that one and the same function will not be applied
                (recursively) a second time, if it has already been
                applied to this parser.

302
303
304
305
        proxied: The original `_parse()`-method is stored here, if a
                proxy (e.g. a tracing debugger) is installed via the
                `set_proxy()`-method.

306
        _grammar:  A reference to the Grammar object to which the parser
307
308
309
                is attached.
    """

310
    def __init__(self) -> None:
311
        # assert isinstance(name, str), str(name)
312
        self.pname = ''               # type: str
313
        self.anonymous = True         # type: bool
314
        self.drop_content = False     # type: bool
315
316
        self.tag_name = self.ptype    # type: str
        self.cycle_detection = set()  # type: Set[ApplyFunc]
317
318
319
        # this indirection is required for Cython-compatibility
        self.__parse = self._parse    # type: ParseMethod
        # self.proxied = None           # type: Optional[ParseMethod]
320
321
322
323
        try:
            self._grammar = GRAMMAR_PLACEHOLDER  # type: Grammar
        except NameError:
            pass
324
325
326
        self.reset()

    def __deepcopy__(self, memo):
327
        """        Deepcopy method of the parser. Upon instantiation of a Grammar-
328
        object, parsers will be deep-copied to the Grammar object. If a
329
        derived parser-class changes the signature of the `__init__`-constructor,
330
331
332
        `__deepcopy__`-method must be replaced (i.e. overridden without
        calling the same method from the superclass) by the derived class.
        """
333
        duplicate = self.__class__()
334
        copy_parser_attrs(self, duplicate)
335
        return duplicate
336

337
    def __repr__(self):
di68kap's avatar
di68kap committed
338
        return self.pname + self.ptype
339
340

    def __str__(self):
di68kap's avatar
di68kap committed
341
        return self.pname + (' = ' if self.pname else '') + repr(self)
342

343
344
345
346
347
348
    @property
    def ptype(self) -> str:
        """Returns a type name for the parser. By default this is the name of
        the parser class with an added leading colon ':'. """
        return ':' + self.__class__.__name__

349
350
351
    @property
    def repr(self) -> str:
        """Returns the parser's name if it has a name and self.__repr___() otherwise."""
di68kap's avatar
di68kap committed
352
        return self.pname if self.pname else self.__repr__()
353

354
355
356
357
    def reset(self):
        """Initializes or resets any parser variables. If overwritten,
        the `reset()`-method of the parent class must be called from the
        `reset()`-method of the derived class."""
358
        self.visited = dict()  # type: Dict[int, Tuple[Optional[Node], StringView]]
eckhart's avatar
eckhart committed
359
        self.recursion_counter = defaultdict(int)  # type: DefaultDict[int, int]
360

361
    # TODO: Outsource this to trace.py !!!
362
363
364
    def _add_resume_notice(self, rest: StringView, err_node: Node) -> None:
        """Adds a resume notice to the error node with information about
        the reentry point and the parser."""
di68kap's avatar
di68kap committed
365
        if not self._grammar.resume_notices__ or self == self._grammar.start_parser__:
366
            return
367
        call_stack = self._grammar.call_stack__
368
        if len(call_stack) >= 2:
369
370
371
            i, N = -2, -len(call_stack)
            while i >= N and call_stack[i][0][0:1] in (':', '/', '"', "'", "`"):
                i -= 1
372
373
            if i >= N and i != -2:
                parent_info = "{}->{}".format(call_stack[i][0], call_stack[-2][0])
374
            else:
375
                parent_info = call_stack[-2][0]
376
377
        else:
            parent_info = "?"
di68kap's avatar
di68kap committed
378
379
        notice = Error('Resuming from parser {} with parser {} at point: {}'
                       .format(self.pname or self.ptype, parent_info, repr(rest[:10])),
380
                       self._grammar.document_length__ - len(rest), Error.RESUME_NOTICE)
381
        self._grammar.tree__.add_error(err_node, notice)
382

eckhart's avatar
eckhart committed
383
    @cython.locals(location=cython.int, gap=cython.int, i=cython.int)
384
385
386
    def __call__(self: 'Parser', text: StringView) -> Tuple[Optional[Node], StringView]:
        """Applies the parser to the given text. This is a wrapper method that adds
        the business intelligence that is common to all parsers. The actual parsing is
387
388
        done in the overridden method `_parse()`. This wrapper-method can be thought of
        as a "parser guard", because it guards the parsing process.
389
        """
390
391
392
393
394
395
396
397
398
        def get_error_node_id(error_node: Node, root_node: RootNode) -> int:
            if error_node:
                error_node_id = id(error_node)
                while error_node_id not in grammar.tree__.error_nodes and error_node.children:
                    error_node = error_node.result[-1]
                    error_node_id = id(error_node)
            else:
                error_node_id = 0

399
        grammar = self._grammar
di68kap's avatar
di68kap committed
400
        location = grammar.document_length__ - text._len  # faster then len(text)?
401
402

        try:
403
404
            # rollback variable changing operation if parser backtracks
            # to a position before the variable changing operation occurred
405
406
407
            if grammar.last_rb__loc__ >= location:
                grammar.rollback_to__(location)

408
            # if location has already been visited by the current parser, return saved result
409
410
            visited = self.visited  # using local variable for better performance
            if location in visited:
411
                # no history recording in case of memoized results
412
                return visited[location]
413
414

            # break left recursion at the maximum allowed depth
415
416
417
            left_recursion_depth__ = grammar.left_recursion_depth__
            if left_recursion_depth__:
                if self.recursion_counter[location] > left_recursion_depth__:
418
419
420
421
                    grammar.recursion_locations__.add(location)
                    return None, text
                self.recursion_counter[location] += 1

422
            # write current step to call stack, if history tracking is configured
423
424
            history_tracking__ = grammar.history_tracking__
            if history_tracking__:
di68kap's avatar
di68kap committed
425
                grammar.call_stack__.append(
426
                    ((self.repr if self.tag_name in (':RegExp', ':Token', ':DropToken')
427
                      else (self.pname or self.tag_name)), location))
428
429
                grammar.moving_forward__ = True

430
            # finally, the actual parser call!
431
            try:
432
                node, rest = self.__parse(text)
433
            except ParserError as pe:
434
                # catching up with parsing after an error occurred
435
                gap = len(text) - len(pe.rest)
di68kap's avatar
di68kap committed
436
                rules = grammar.resume_rules__.get(self.pname, [])
437
                rest = pe.rest[len(pe.node):]
438
439
                i = reentry_point(rest, rules, grammar.comment_rx__,
                                  grammar.reentry_search_window__)
440
                if i >= 0 or self == grammar.start_parser__:
441
                    assert pe.node.children or (not pe.node.result)
442
                    # apply reentry-rule or catch error at root-parser
di68kap's avatar
di68kap committed
443
444
                    # if i < 0:
                    #     i = 1
445
446
                    try:
                        zombie = pe.node[ZOMBIE_TAG]
447
                    except (KeyError, ValueError):
448
449
450
451
452
453
454
455
                        zombie = None
                    if zombie and not zombie.result:
                        zombie.result = rest[:i]
                        tail = tuple()
                    else:
                        nd = Node(ZOMBIE_TAG, rest[:i]).with_pos(location)
                        nd.attr['err'] = pe.error.message
                        tail = (nd,)
456
                    rest = rest[i:]
457
458
                    if pe.first_throw:
                        node = pe.node
459
                        node.result = node.children + tail
460
                    else:
461
462
                        node = Node(
                            self.tag_name,
di68kap's avatar
di68kap committed
463
464
                            (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) + tail) \
                            .with_pos(location)
465
                    # self._add_resume_notice(rest, node)
466
                elif pe.first_throw:
eckhart's avatar
eckhart committed
467
                    # TODO: Will this option be needed, if history tracking is deferred to module "trace"?
468
                    if history_tracking__:  grammar.call_stack__.pop()
469
                    raise ParserError(pe.node, pe.rest, pe.error, first_throw=False)
470
                elif grammar.tree__.errors[-1].code == Error.MANDATORY_CONTINUATION_AT_EOF:
471
                    node = Node(self.tag_name, pe.node).with_pos(location)  # try to create tree as faithful as possible
472
                else:
473
474
                    result = (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) if gap \
                        else pe.node  # type: ResultType
475
                    if history_tracking__:  grammar.call_stack__.pop()
476
477
                    raise ParserError(Node(self.tag_name, result).with_pos(location),
                                      text, pe.error, first_throw=False)
478
                self._add_resume_notice(rest, node)
479
                grammar.most_recent_error__ = pe.error  # needed for history tracking
480

481
            if left_recursion_depth__:
482
483
484
485
486
487
                self.recursion_counter[location] -= 1
                # don't clear recursion_locations__ !!!

            if node is None:
                # retrieve an earlier match result (from left recursion) if it exists
                if location in grammar.recursion_locations__:
488
489
                    if location in visited:
                        node, rest = visited[location]
490
                        if location != grammar.last_recursion_location__:
491
492
493
                            grammar.tree__.add_error(
                                node, Error("Left recursion encountered. "
                                            "Refactor grammar to avoid slow parsing.",
494
495
                                            node.pos if node else location,
                                            Error.LEFT_RECURSION_WARNING))
496
                            error_id = id(node)
497
                            grammar.last_recursion_location__ = location
498
499
500
501
                    # don't overwrite any positive match (i.e. node not None) in the cache
                    # and don't add empty entries for parsers returning from left recursive calls!
                elif grammar.memoization__:
                    # otherwise also cache None-results
502
                    visited[location] = (None, rest)
503
            else:
504
                # assert node._pos < 0 or node == EMPTY_NODE
505
                # if node._pos != EMPTY_NODE:
506
                node._pos = location
507
508
                # assert node._pos >= 0 or node == EMPTY_NODE, \
                #     str("%i < %i" % (grammar.document_length__, location))
509
510
511
512
513
514
515
                if (grammar.last_rb__loc__ < location
                        and (grammar.memoization__ or location in grammar.recursion_locations__)):
                    # - variable manipulating parsers will not be entered into the cache,
                    #   because caching would interfere with changes of variable state
                    # - in case of left recursion, the first recursive step that
                    #   matches will store its result in the cache
                    # TODO: need a unit-test concerning interference of variable manipulation and left recursion algorithm?
516
                    visited[location] = (node, rest)
517
518
519

            # Mind that memoized parser calls will not appear in the history record!
            # Does this make sense? Or should it be changed?
520
            if history_tracking__:
521
                # don't track returning parsers except in case an error has occurred
522
                if grammar.moving_forward__:
523
                    record = HistoryRecord(grammar.call_stack__, node, text,
di68kap's avatar
di68kap committed
524
                                           grammar.line_col__(text))
525
                    grammar.history__.append(record)
526
                elif grammar.most_recent_error__:
527
528
529
                    # error_nid = id(node)  # type: int
                    # if error_nid in grammar.tree__.error_nodes:
                    record = HistoryRecord(grammar.call_stack__, node, text,
di68kap's avatar
di68kap committed
530
                                           grammar.line_col__(text),
531
532
                                           [grammar.most_recent_error__])
                    grammar.most_recent_error__ = None
533
                    grammar.history__.append(record)
534
535
536
537
                grammar.moving_forward__ = False
                grammar.call_stack__.pop()

        except RecursionError:
538
            node = Node(ZOMBIE_TAG, str(text[:min(10, max(1, text.find("\n")))]) + " ...")
539
540
541
542
543
544
            node._pos = location
            grammar.tree__.new_error(node, "maximum recursion depth of parser reached; "
                                           "potentially due to too many errors!")
            rest = EMPTY_STRING_VIEW

        return node, rest
545
546
547
548
549
550
551
552
553
554
555
556

    def __add__(self, other: 'Parser') -> 'Series':
        """The + operator generates a series-parser that applies two
        parsers in sequence."""
        return Series(self, other)

    def __or__(self, other: 'Parser') -> 'Alternative':
        """The | operator generates an alternative parser that applies
        the first parser and, if that does not match, the second parser.
        """
        return Alternative(self, other)

557
558
559
560
561
562
    def _parse(self, text: StringView) -> Tuple[Optional[Node], StringView]:
        """Applies the parser to the given `text` and returns a node with
        the results or None as well as the text at the position right behind
        the matching string."""
        raise NotImplementedError

563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
    def set_proxy(self, proxy: Optional[ParseFunc]):
        """Sets a proxy that replaces the _parse()-method. The original
        parse-method is copied to the `proxied`-filed of the Parser object and
        can be called by the proxy. Call `set_proxy` with `None` to remove
        a previously set proxy. Typical use case is the installation of a
        tracing debugger. See module `trace`.
        """
        if proxy is None:
            self.__parse = self._parse
        else:
            if type(proxy) != type(self._parse):
                # assume that proxy is a function
                proxy = proxy.__get__(self, type(self))
            else:
                # if proxy is a method it must be a method od self
                assert proxy.__self__ == self
            self.__parse = proxy

581
    @property
eckhart's avatar
eckhart committed
582
    def grammar(self) -> 'Grammar':
583
584
585
586
587
        try:
            if self._grammar != GRAMMAR_PLACEHOLDER:
                return self._grammar
            else:
                raise AssertionError('Grammar has not yet been set!')
588
589
        except (AttributeError, NameError):
            raise AttributeError('Parser placeholder does not have a grammar!')
590
591
592

    @grammar.setter
    def grammar(self, grammar: 'Grammar'):
593
594
595
596
597
598
599
600
601
        try:
            if self._grammar == GRAMMAR_PLACEHOLDER:
                self._grammar = grammar
                # self._grammar_assigned_notifier()
            elif self._grammar != grammar:
                  raise AssertionError("Parser has already been assigned"
                                       "to a different Grammar object!")
        except AttributeError:
            pass  # ignore setting of grammar attribute for placeholder parser
602
603
        except NameError:  # Cython: No access to GRAMMA_PLACEHOLDER, yet :-(
            self._grammar = grammar
604

605
606
607
608
609
610
    def sub_parsers(self) -> List['Parser']:
        """Returns the list of sub-parsers if there are any.
        Overridden by Unary, Nary and Forward.
        """
        return []

eckhart's avatar
eckhart committed
611
    def _apply(self, func: ApplyFunc, flip: FlagFunc) -> bool:
612
613
        """
        Applies function `func(parser)` recursively to this parser and all
eckhart's avatar
eckhart committed
614
615
616
617
618
619
620
621
622
        descendant parsers, if any exist.

        In order to break cycles, function `flip` is called, which should
        return `True`, if this parser has already been visited. If not, it
        flips the cycle detection flag and returns `False`.

        This is a protected function and should not called from outside
        class Parser or any of its descendants. The entry point for external
        calls is the method `apply()` without underscore!
623
        """
eckhart's avatar
eckhart committed
624
        if flip(func, self.cycle_detection):
625
626
627
            return False
        else:
            func(self)
628
629
            for parser in self.sub_parsers():
                parser._apply(func, flip)
630
631
            return True

eckhart's avatar
eckhart committed
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
    def apply(self, func: ApplyFunc):
        """
        Applies function `func(parser)` recursively to this parser and all
        descendant parsers, if any exist. Traversal is pre-order.
        """
        def positive_flip(f: ApplyFunc, flagged: Set[Callable]) -> bool:
            """Returns True, if function `f` has already been applied to this
            parser and sets the flag accordingly. Interprets `f in flagged == True`
            as meaning that `f` has already been applied."""
            if f in flagged:
                return True
            else:
                flagged.add(f)
                return False

        def negative_flip(f: ApplyFunc, flagged: Set[Callable]) -> bool:
            """Returns True, if function `f` has already been applied to this
            parser and sets the flag accordingly. Interprets `f in flagged == False`
            as meaning that `f` has already been applied."""
            if f not in flagged:
                return True
            else:
                flagged.remove(f)
                return False

        if func in self.cycle_detection:
            self._apply(func, negative_flip)
        else:
            self._apply(func, positive_flip)

662

eckhart's avatar
eckhart committed
663
664
def Drop(parser: Parser) -> Parser:
    """Returns the parser with the `parser.drop_content`-property set to `True`."""
Eckhart Arnold's avatar
Eckhart Arnold committed
665
    assert parser.anonymous, "Parser must be anonymous to be allowed to drop ist content."
eckhart's avatar
eckhart committed
666
667
668
    if isinstance(parser, Forward):
        cast(Forward, parser).parser.drop_content = True
    parser.drop_content = True
Eckhart Arnold's avatar
Eckhart Arnold committed
669
    return parser
eckhart's avatar
eckhart committed
670
671


672
PARSER_PLACEHOLDER = Parser()
673
674
675
676
677
678
679
680


########################################################################
#
# Grammar class, central administration of all parser of a grammar
#
########################################################################

681
682
def mixin_comment(whitespace: str, comment: str) -> str:
    """
683
    Returns a regular expression pattern that merges comment and whitespace
684
    regexps. Thus comments can occur wherever whitespace is allowed
685
686
687
688
689
690
    and will be skipped just as implicit whitespace.

    Note, that because this works on the level of regular expressions,
    nesting comments is not possible. It also makes it much harder to
    use directives inside comments (which isn't recommended, anyway).
    """
691
692
693
    if comment:
        return '(?:' + whitespace + '(?:' + comment + whitespace + ')*)'
    return whitespace
694
695


Eckhart Arnold's avatar
Eckhart Arnold committed
696
697
def mixin_noempty(whitespace: str) -> str:
    r"""
698
699
700
701
702
703
704
705
706
707
708
709
710
711
    Returns a regular expression pattern that matches only if the regular
    expression pattern `whitespace` matches AND if the match is not empty.

    If `whitespace` already matches the empty string '', then it will be
    returned unaltered.

    WARNING: `non_empty_ws` does not work regular expressions the matched
    strings of which can be followed by a symbol that can also occur at
    the start of the regular expression.

    In particular, it does not work for fixed size regular expressions,
    that ist / / or /   / or /\t/ won't work, but / */ or /\s*/ or /\s+/
    do work. There is no test for this. Fixed sizes regular expressions
    run through `non_empty_ws` will not match at any more if they are applied
Eckhart Arnold's avatar
Eckhart Arnold committed
712
713
714
715
716
    to the beginning or the middle of a sequence of whitespaces!

    In order to be safe, you whitespace regular expressions should follow
    the rule: "Whitespace cannot be followed by whitespace" or "Either
    grab it all or leave it all".
717
718
719
720
721
722
723
724
725
726

    :param whitespace: a regular expression pattern
    :return: new regular expression pattern that does not match the empty
        string '' any more.
    """
    if re.match(whitespace, ''):
        return r'(?:(?=(.|\n))' + whitespace + r'(?!\1))'
    return whitespace


727
class UnknownParserError(KeyError):
eckhart's avatar
eckhart committed
728
    """UnknownParserError is raised if a Grammar object is called with a
729
    parser that does not exist or if in the course of parsing a parser
eckhart's avatar
eckhart committed
730
    is referred to that does not exist."""
731
732


733
GrammarErrorType = Tuple[str, Parser, Error]      # TODO: replace with a named tuple?
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750


class GrammarError(Exception):
    """GrammarError will be raised if static analysis reveals errors
    in the grammar.
    """
    def __init__(self, static_analysis_result: List[GrammarErrorType]):
        assert static_analysis_result  # must not be empty
        self.errors = static_analysis_result

    def __str__(self):
        if len(self.errors) == 1:
            return str(self.errors[0][2])
        return '\n' + '\n'.join(("%i. " % (i + 1) + str(err_tuple[2]))
                                for i, err_tuple in enumerate(self.errors))


751
752
753
754
755
756
757
758
759
760
761
762
763
class Grammar:
    r"""
    Class Grammar directs the parsing process and stores global state
    information of the parsers, i.e. state information that is shared
    accross parsers.

    Grammars are basically collections of parser objects, which are
    connected to an instance object of class Grammar. There exist two
    ways of connecting parsers to grammar objects: Either by passing
    the root parser object to the constructor of a Grammar object
    ("direct instantiation"), or by assigning the root parser to the
    class variable "root__" of a descendant class of class Grammar.

eckhart's avatar
eckhart committed
764
    Example for direct instantiation of a grammar::
765

766
        >>> number = RE(r'\d+') + RE(r'\.') + RE(r'\d+') | RE(r'\d+')
767
768
769
770
771
772
773
774
775
776
777
778
779
780
        >>> number_parser = Grammar(number)
        >>> number_parser("3.1416").content
        '3.1416'

    Collecting the parsers that define a grammar in a descendant class of
    class Grammar and assigning the named parsers to class variables
    rather than global variables has several advantages:

    1. It keeps the namespace clean.

    2. The parser names of named parsers do not need to be passed to the
       constructor of the Parser object explicitly, but it suffices to
       assign them to class variables, which results in better
       readability of the Python code.
781
       See classmethod `Grammar._assign_parser_names__()`
782
783

    3. The parsers in the class do not necessarily need to be connected
784
785
       to one single root parser, which is helpful for testing and when
       building up a parser gradually from several components.
786
787
788
789
790
791
792

    As a consequence, though, it is highly recommended that a Grammar
    class should not define any other variables or methods with names
    that are legal parser names. A name ending with a double
    underscore '__' is *not* a legal parser name and can safely be
    used.

793
    Example::
794
795
796
797
798
799
800
801
802

        class Arithmetic(Grammar):
            # special fields for implicit whitespace and comment configuration
            COMMENT__ = r'#.*(?:\n|$)'  # Python style comments
            wspR__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)

            # parsers
            expression = Forward()
            INTEGER = RE('\\d+')
803
804
805
            factor = INTEGER | TKN("(") + expression + TKN(")")
            term = factor + ZeroOrMore((TKN("*") | TKN("/")) + factor)
            expression.set(term + ZeroOrMore((TKN("+") | TKN("-")) + term))
806
807
808
809
            root__ = expression

    Upon instantiation the parser objects are deep-copied to the
    Grammar object and assigned to object variables of the same name.
810
811
812
813
814
    For any parser that is directly assigned to a class variable the
    field `parser.pname` contains the variable name after instantiation
    of the Grammar class. The parser will never the less remain anonymous
    with respect to the tag names of the nodes it generates, if its name
    is matched by the `anonymous__` regular expression.
815
    If one and the same parser is assigned to several class variables
816
    such as, for example, the parser `expression` in the example above,
817
    which is also assigned to `root__`, the first name sticks.
818
819
820
821
822
823
824
825
826
827
828
829

    Grammar objects are callable. Calling a grammar object with a UTF-8
    encoded document, initiates the parsing of the document with the
    root parser. The return value is the concrete syntax tree. Grammar
    objects can be reused (i.e. called again) after parsing. Thus, it
    is not necessary to instantiate more than one Grammar object per
    thread.

    Grammar classes contain a few special class fields for implicit
    whitespace and comments that should be overwritten, if the defaults
    (no comments, horizontal right aligned whitespace) don't fit:

830
    Class Attributes:
831
832
833
834
        root__:  The root parser of the grammar. Theoretically, all parsers of the
                 grammar should be reachable by the root parser. However, for testing
                 of yet incomplete grammars class Grammar does not assume that this
                 is the case.
835

836
837
838
        resume_rules__: A mapping of parser names to a list of regular expressions
                that act as rules to find the reentry point if a ParserError was
                thrown during the execution of the parser with the respective name.
Eckhart Arnold's avatar
Eckhart Arnold committed
839

840
841
842
843
844
        anonymous__: A regular expression to identify names of parsers that are
                assigned to class fields but shall never the less yield anonymous
                nodes (i.e. nodes the tag name of which starts with a colon ":"
                followed by the parser's class name). The default is to treat all
                parsers starting with an underscore as anonymous in addition to those
845
846
                parsers that are not directly assigned to a class field.

eckhart's avatar
eckhart committed
847
        parser_initialization__:  Before the grammar class (!) has been initialized,
848
                 which happens upon the first time it is instantiated (see
849
                 `:func:_assign_parser_names()` for an explanation), this class
850
851
                 field contains a value other than "done". A value of "done" indicates
                 that the class has already been initialized.
852

853
854
855
856
857
858
859
        static_analysis_pending__: True as long as no static analysis (see the method
                with the same name for more information) has been done to check
                parser tree for correctness. Static analysis
                is done at instantiation and the flag is then set to false, but it
                can also be carried out once the class has been generated
                (by DHParser.ebnf.EBNFCompiler) and then be set to false in the
                definition of the grammar class already.
860

eckhart's avatar
eckhart committed
861
862
863
864
        python__src__:  For the purpose of debugging and inspection, this field can
                 take the python src of the concrete grammar class
                 (see `dsl.grammar_provider`).

865
    Instance Attributes:
866
867
        all_parsers__:  A set of all parsers connected to this grammar object

868
869
        comment_rx__:  The compiled regular expression for comments. If no
                comments have been defined, it defaults to RX_NEVER_MATCH
870
871
                This instance-attribute will only be defined if a class-attribute
                with the same name does not already exist!
872

eckhart's avatar
eckhart committed
873
874
875
876
        start_parser__:  During parsing, the parser with which the parsing process
                was started (see method `__call__`) or `None` if no parsing process
                is running.

877
878
879
880
881
882
883
        _dirty_flag__:  A flag indicating that the Grammar has been called at
                least once so that the parsing-variables need to be reset
                when it is called again.

        document__:  the text that has most recently been parsed or that is
                currently being parsed.

eckhart's avatar
eckhart committed
884
885
        document_length__:  the length of the document.

886
887
        document_lbreaks__ (property):  list of linebreaks within the document,
                starting with -1 and ending with EOF. This helps generating line
888
                and column number for history recording and will only be
889
                initialized if :attr:`history_tracking__` is true.
890

891
892
893
894
895
        tree__: The root-node of the parsing tree. This variable is available
               for error-reporting already during parsing  via
               ``self.grammar.tree__.add_error``, but it references the full
               parsing tree only after parsing has been finished.

896
        _reversed__:  the same text in reverse order - needed by the `Lookbehind`-
897
898
899
                parsers.

        variables__:  A mapping for variable names to a stack of their respective
900
901
                string values - needed by the :class:`Capture`-, :class:`Retrieve`-
                and :class:`Pop`-parsers.
902
903

        rollback__:  A list of tuples (location, rollback-function) that are
904
905
906
907
                deposited by the :class:`Capture`- and :class:`Pop`-parsers.
                If the parsing process reaches a dead end then all
                rollback-functions up to the point to which it retreats will be
                called and the state of the variable stack restored accordingly.
908
909
910

        last_rb__loc__:  The last, i.e. most advanced location in the text
                where a variable changing operation occurred. If the parser
911
912
                backtracks to a location at or before last_rb__loc__ (i.e.
                location <= last_rb__loc__) then a rollback of all variable
913
914
                changing operations is necessary that occurred after the
                location to which the parser backtracks. This is done by
915
                calling method :func:`rollback_to__(location)`.
916

di68kap's avatar
di68kap committed
917
918
919
        call_stack__:  A stack of the tag names and locations of all parsers
                in the call chain to the currently processed parser during
                parsing. The call stack can be thought of as a breadcrumb trail.
920
                This is required for recording the parser history (for debugging)
921
922
923
                and, eventually, i.e. one day in the future, for tracing through
                the parsing process.

924
925
926
927
        history__:  A list of history records. A history record is appended to
                the list each time a parser either matches, fails or if a
                parser-error occurs. See class `log.HistoryRecord`. History
                records store copies of the current call stack.
928
929
930
931

        moving_forward__: This flag indicates that the parsing process is currently
                moving forward . It is needed to reduce noise in history recording
                and should not be considered as having a valid value if history
932
                recording is turned off! (See :func:`Parser.__call__`)
933
934
935
936

        recursion_locations__:  Stores the locations where left recursion was
                detected. Needed to provide minimal memoization for the left
                recursion detection algorithm, but, strictly speaking, superfluous
937
938
939
940
941
                if full memoization is enabled. (See :func:`Parser.__call__()`)

        last_recursion_location__:  Last location where left recursion was
                detected. This is used to avoid reduplicating warning messages
                about left recursion.
942

943
944
945
        most_recent_error__: The most recent parser error that has occurred
                or `None`. This can be read by tracers. See module `trace`

946
947
948
949
950
        memoization__:  Turns full memoization on or off. Turning memoization off
                results in less memory usage and sometimes reduced parsing time.
                In some situations it may drastically increase parsing time, so
                it is safer to leave it on. (Default: on)

951
952
953
954
        # Configuration parameters. These values of theses parameters are copied
                from the global configuration in the constructor of the Grammar
                object. (see mpodule `configuration.py`)

955
956
957
        flatten_tree__:  If True (default), anonymous nodes will be flattened
                during parsing already. This greatly reduces the concrete syntax
                tree and simplifies and speeds up abstract syntax tree generation.
958
                Default is on.
959
960
961

        left_recursion_depth__: the maximum allowed depth for left-recursion.
                A depth of zero means that no left recursion handling will
962
                take place. Default is 5.
963
964
965

        max_parser_dropouts__: Maximum allowed number of retries after errors
                where the parser would exit before the complete document has
966
967
                been parsed. Default is 1, as usually the retry-attemts lead
                to a proliferation of senseless error messages.
968
969
970

        reentry_search_window__: The number of following characters that the
                parser considers when searching a reentry point when a syntax error
971
972
973
974
975
976
977
978
979
                has been encountered. Default is 10.000 characters.

        history_tracking__:  A flag indicating that the parsing history shall
                be tracked. Default is off.

        resume_notices__: When resuming after an error a notice message is added
               in addition to the error message to report where, and, if history
               tracking is turned on, with which parser the parsing process
               will be resumed. Default is off.
980
    """
eckhart's avatar
eckhart committed
981
    python_src__ = ''  # type: str
982
    root__ = PARSER_PLACEHOLDER  # type: Parser
983
    # root__ must be overwritten with the root-parser by grammar subclass
eckhart's avatar
eckhart committed
984
    parser_initialization__ = ["pending"]  # type: List[str]
eckhart's avatar
eckhart committed
985
    resume_rules__ = dict()  # type: Dict[str, ResumeList]
986
    anonymous__ = RX_NEVER_MATCH  # type: RxPatternType
987
    # some default values
eckhart's avatar
eckhart committed
988
989
    COMMENT__ = r''  # type: str  # r'#.*(?:\n|$)'
    WSP_RE__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)  # type: str
990
    static_analysis_pending__ = [True]  # type: List[bool]
991
992
993
994
995


    @classmethod
    def _assign_parser_names__(cls):
        """
di68kap's avatar
di68kap committed
996
        Initializes the `parser.pname` fields of those
997
        Parser objects that are directly assigned to a class field with
998
        the field's name, e.g.::
999

1000
            class Grammar(Grammar):