parse.py 125 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
eckhart's avatar
eckhart committed
35
from typing import Callable, cast, List, Tuple, Set, Dict, \
36
    DefaultDict, Sequence, Union, Optional, Any
37

eckhart's avatar
eckhart committed
38
from DHParser.configuration import get_config_value
39
from DHParser.error import Error
eckhart's avatar
eckhart committed
40
from DHParser.log import CallItem, HistoryRecord
41
from DHParser.preprocess import BEGIN_TOKEN, END_TOKEN, RX_TOKEN_NAME
42
from DHParser.stringview import StringView, EMPTY_STRING_VIEW
eckhart's avatar
eckhart committed
43
from DHParser.syntaxtree import ChildrenType, Node, 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
    abbreviate_middle, RX_NEVER_MATCH, RxPatternType, linebreaks, line_col
47

48
__all__ = ('ParserError',
eckhart's avatar
eckhart committed
49
50
51
           'ApplyFunc',
           'FlagFunc',
           'ParseFunc',
52
           'Parser',
53
           'UnknownParserError',
54
55
           'GrammarErrorType',
           'GrammarError',
56
57
           'Grammar',
           'PreprocessorToken',
58
           'Token',
59
           'DropToken',
60
           'RegExp',
61
62
           'RE',
           'TKN',
63
           'Whitespace',
64
           'DropRegExp',
65
           'mixin_comment',
di68kap's avatar
di68kap committed
66
           'mixin_nonempty',
67
           'MetaParser',
eckhart's avatar
eckhart committed
68
69
           'UnaryParser',
           'NaryParser',
70
           'Drop',
71
72
73
74
           'Synonym',
           'Option',
           'ZeroOrMore',
           'OneOrMore',
75
           'NO_MANDATORY',
Eckhart Arnold's avatar
Eckhart Arnold committed
76
           'MandatoryNary',
77
78
79
80
81
           'Series',
           'Alternative',
           'AllOf',
           'SomeOf',
           'Unordered',
82
           'INFINITE',
83
           'Interleave',
eckhart's avatar
eckhart committed
84
           'Required',
85
86
87
88
89
           'Lookahead',
           'NegativeLookahead',
           'Lookbehind',
           'NegativeLookbehind',
           'last_value',
90
91
           'optional_last_value',
           'matching_bracket',
92
93
94
           'Capture',
           'Retrieve',
           'Pop',
95
           'Forward')
96
97
98
99


########################################################################
#
100
# ParserError class
101
102
103
104
#
########################################################################


Eckhart Arnold's avatar
Eckhart Arnold committed
105
106
107
class ParserError(Exception):
    """
    A `ParserError` is thrown for those parser errors that allow the
108
    controlled re-entrance of the parsing process after the error occurred.
Eckhart Arnold's avatar
Eckhart Arnold committed
109
    If a reentry-rule has been configured for the parser where the error
110
    occurred, the parser guard can resume the parsing process.
Eckhart Arnold's avatar
Eckhart Arnold committed
111
112

    Currently, the only case when a `ParserError` is thrown (and not some
113
114
    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
115
    """
eckhart's avatar
eckhart committed
116
    def __init__(self, node: Node, rest: StringView, error: Error, first_throw: bool):
eckhart's avatar
eckhart committed
117
        assert node is not None
eckhart's avatar
eckhart committed
118
119
120
        self.node = node    # type: Node
        self.rest = rest    # type: StringView
        self.error = error  # type: Error
121
        self.first_throw = first_throw  # type: bool
eckhart's avatar
eckhart committed
122
        self.frozen_callstack = tuple()  # type: Tuple[CallItem, ...]  # tag_name, location
Eckhart Arnold's avatar
Eckhart Arnold committed
123

124
    def __str__(self):
125
        return "%i: %s    %s" % (self.node.pos, str(self.rest[:25]), repr(self.node))
126

Eckhart Arnold's avatar
Eckhart Arnold committed
127

128
ResumeList = List[RxPatternType]  # list of regular expressiones
Eckhart Arnold's avatar
Eckhart Arnold committed
129
130


eckhart's avatar
eckhart committed
131
@cython.locals(upper_limit=cython.int, closest_match=cython.int, pos=cython.int)
132
133
134
def reentry_point(rest: StringView,
                  rules: ResumeList,
                  comment_regex,
135
                  search_window: int = -1) -> int:
Eckhart Arnold's avatar
Eckhart Arnold committed
136
137
    """
    Finds the point where parsing should resume after a ParserError has been caught.
138
    The algorithm makes sure that this reentry-point does not lie inside a comment.
139
140
141
    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
142
143
    Args:
        rest:  The rest of the parsed text or, in other words, the point where
144
145
146
147
            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.
148
        comment_regex: A regular expression object that matches comments.
149
150
        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
151
    Returns:
152
153
        The integer index of the closest reentry point or -1 if no reentry-point
        was found.
Eckhart Arnold's avatar
Eckhart Arnold committed
154
    """
155
    upper_limit = len(rest) + 1
156
    closest_match = upper_limit
157
158
    comments = None  # typ: Optional[Iterator]

eckhart's avatar
eckhart committed
159
    @cython.locals(a=cython.int, b=cython.int)
160
161
162
163
164
165
166
167
168
169
170
    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

171
172
    # def str_search(s, start: int = 0) -> Tuple[int, int]:
    #     nonlocal rest
173
    #     return rest.find(s, start, start + search_window), len(s)
174

eckhart's avatar
eckhart committed
175
    @cython.locals(start=cython.int, end=cython.int)
176
177
    def rx_search(rx, start: int = 0) -> Tuple[int, int]:
        nonlocal rest
178
        m = rest.search(rx, start, start + search_window)
179
        if m:
180
181
            begin, end = m.span()
            return rest.index(begin), end - begin
182
183
        return -1, 0

eckhart's avatar
eckhart committed
184
    @cython.locals(a=cython.int, b=cython.int, k=cython.int, length=cython.int)
185
186
187
188
189
    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()
190
191
192
        # 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)
193
194
            while a < b <= k:
                a, b = next_comment()
195
        return k + length if k >= 0 else upper_limit
196

197
    # find closest match
Eckhart Arnold's avatar
Eckhart Arnold committed
198
    for rule in rules:
199
        comments = rest.finditer(comment_regex)
200
201
202
        assert not isinstance(rule, str), \
            'Strings not allowed as search rules, use a regular expression instead.'
        pos = entry_point(rx_search, rule)
203
        closest_match = min(pos, closest_match)
204

205
    # in case no rule matched return -1
206
207
208
    if closest_match == upper_limit:
        closest_match = -1
    return closest_match
Eckhart Arnold's avatar
Eckhart Arnold committed
209
210


211
212
213
214
215
216
217
########################################################################
#
# Parser base class
#
########################################################################


218
ApplyFunc = Callable[['Parser'], Optional[bool]]  # A return value of True stops any further application
eckhart's avatar
eckhart committed
219
FlagFunc = Callable[[ApplyFunc, Set[ApplyFunc]], bool]
eckhart's avatar
eckhart committed
220
ParseFunc = Callable[[StringView], Tuple[Optional[Node], StringView]]
eckhart's avatar
eckhart committed
221

222
223
224
225
226
# The global flag STATIC_ANALYSIS_PENGING signals the constructors
# of Parser-classes not to raise exceptions for errors that will
# be reported more preciseley in the static analysis
STATIC_ANALYSIS_PENDING = False

eckhart's avatar
eckhart committed
227

228
class Parser:
229
230
231
232
233
234
235
236
237
238
239
240
241
242
    """
    (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
243
    1. *Named parsers* for which a name is set in field `parser.pname`.
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
       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:
267

268
269
        pname:  The parser's name or a (possibly empty) alias name in case
                of an anonymous parser.
270

271
272
273
274
275
        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] == ":"`.
276

277
278
279
280
        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
281
282
283
                dropped from the concrete syntax tree already. Only
                anonymous (or pseudo-anonymous) parsers are allowed to
                drop content.
284

285
        tag_name: The tag_name for the nodes that are created by
286
287
                the parser. If the parser is named, this is the same as
                `pname`, otherwise it is the name of the parser's type.
288

289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
        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.

304
305
306
307
        proxied: The original `_parse()`-method is stored here, if a
                proxy (e.g. a tracing debugger) is installed via the
                `set_proxy()`-method.

308
        _grammar:  A reference to the Grammar object to which the parser
309
310
311
                is attached.
    """

312
    def __init__(self) -> None:
313
        # assert isinstance(name, str), str(name)
314
        self.pname = ''               # type: str
315
        self.anonymous = True         # type: bool
316
        self.drop_content = False     # type: bool
317
318
        self.tag_name = self.ptype    # type: str
        self.cycle_detection = set()  # type: Set[ApplyFunc]
319
        # this indirection is required for Cython-compatibility
Eckhart Arnold's avatar
Eckhart Arnold committed
320
        self._parse_proxy = self._parse    # type: ParseFunc
eckhart's avatar
eckhart committed
321
        # self.proxied = None           # type: Optional[ParseFunc]
322
323
324
325
        try:
            self._grammar = GRAMMAR_PLACEHOLDER  # type: Grammar
        except NameError:
            pass
326
327
328
        self.reset()

    def __deepcopy__(self, memo):
329
        """Deepcopy method of the parser. Upon instantiation of a Grammar-
330
        object, parsers will be deep-copied to the Grammar object. If a
331
        derived parser-class changes the signature of the `__init__`-constructor,
332
333
334
        `__deepcopy__`-method must be replaced (i.e. overridden without
        calling the same method from the superclass) by the derived class.
        """
335
        duplicate = self.__class__()
336
        copy_parser_base_attrs(self, duplicate)
337
        return duplicate
338

339
    def __repr__(self):
di68kap's avatar
di68kap committed
340
        return self.pname + self.ptype
341
342

    def __str__(self):
di68kap's avatar
di68kap committed
343
        return self.pname + (' = ' if self.pname else '') + repr(self)
344

345
346
347
348
349
350
    @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__

351
352
353
    @property
    def repr(self) -> str:
        """Returns the parser's name if it has a name and self.__repr___() otherwise."""
di68kap's avatar
di68kap committed
354
        return self.pname if self.pname else self.__repr__()
355

356
357
358
359
    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."""
360
        self.visited = dict()  # type: Dict[int, Tuple[Optional[Node], StringView]]
eckhart's avatar
eckhart committed
361
        self.recursion_counter = defaultdict(int)  # type: DefaultDict[int, int]
362

eckhart's avatar
eckhart committed
363
    @cython.locals(location=cython.int, gap=cython.int, i=cython.int)
364
365
366
    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
367
368
        done in the overridden method `_parse()`. This wrapper-method can be thought of
        as a "parser guard", because it guards the parsing process.
369
        """
eckhart's avatar
eckhart committed
370
371
372
373
374
375
376
377
        # 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
378

379
        grammar = self._grammar
di68kap's avatar
di68kap committed
380
        location = grammar.document_length__ - text._len  # faster then len(text)?
381
382

        try:
383
384
            # rollback variable changing operation if parser backtracks
            # to a position before the variable changing operation occurred
385
            if grammar.last_rb__loc__ > location:
386
387
                grammar.rollback_to__(location)

388
            # if location has already been visited by the current parser, return saved result
389
390
            visited = self.visited  # using local variable for better performance
            if location in visited:
391
                # no history recording in case of memoized results
392
                return visited[location]
393
394

            # break left recursion at the maximum allowed depth
395
396
397
            left_recursion_depth__ = grammar.left_recursion_depth__
            if left_recursion_depth__:
                if self.recursion_counter[location] > left_recursion_depth__:
398
399
400
401
                    grammar.recursion_locations__.add(location)
                    return None, text
                self.recursion_counter[location] += 1

402
            # finally, the actual parser call!
403
            try:
Eckhart Arnold's avatar
Eckhart Arnold committed
404
                node, rest = self._parse_proxy(text)
405
            except ParserError as pe:
406
                # catching up with parsing after an error occurred
407
                gap = len(text) - len(pe.rest)
di68kap's avatar
di68kap committed
408
                rules = grammar.resume_rules__.get(self.pname, [])
409
                rest = pe.rest[len(pe.node):]
410
411
                i = reentry_point(rest, rules, grammar.comment_rx__,
                                  grammar.reentry_search_window__)
412
                if i >= 0 or self == grammar.start_parser__:
413
                    assert pe.node.children or (not pe.node.result)
414
                    # apply reentry-rule or catch error at root-parser
eckhart's avatar
eckhart committed
415
                    if i < 0:  i = 0
416
                    try:
417
                        zombie = pe.node.pick_child(ZOMBIE_TAG)  # type: Optional[Node]
418
                    except (KeyError, ValueError):
419
420
421
                        zombie = None
                    if zombie and not zombie.result:
                        zombie.result = rest[:i]
eckhart's avatar
eckhart committed
422
                        tail = tuple()  # type: ChildrenType
423
424
                    else:
                        nd = Node(ZOMBIE_TAG, rest[:i]).with_pos(location)
eckhart's avatar
eckhart committed
425
                        # nd.attr['err'] = pe.error.message
426
                        tail = (nd,)
427
                    rest = rest[i:]
428
429
                    if pe.first_throw:
                        node = pe.node
430
                        node.result = node.children + tail
431
                    else:
432
433
                        node = Node(
                            self.tag_name,
di68kap's avatar
di68kap committed
434
435
                            (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) + tail) \
                            .with_pos(location)
436
                elif pe.first_throw:
eckhart's avatar
eckhart committed
437
                    # TODO: Is this case still needed with module "trace"?
438
                    raise ParserError(pe.node, pe.rest, pe.error, first_throw=False)
439
                elif grammar.tree__.errors[-1].code == Error.MANDATORY_CONTINUATION_AT_EOF:
eckhart's avatar
eckhart committed
440
441
                    # try to create tree as faithful as possible
                    node = Node(self.tag_name, pe.node).with_pos(location)
442
                else:
443
444
                    result = (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) if gap \
                        else pe.node  # type: ResultType
445
446
                    raise ParserError(Node(self.tag_name, result).with_pos(location),
                                      text, pe.error, first_throw=False)
447

448
            if left_recursion_depth__:
449
450
451
452
453
454
                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__:
455
456
                    if location in visited:
                        node, rest = visited[location]
457
                        if location != grammar.last_recursion_location__:
458
459
460
                            grammar.tree__.add_error(
                                node, Error("Left recursion encountered. "
                                            "Refactor grammar to avoid slow parsing.",
461
462
                                            node.pos if node else location,
                                            Error.LEFT_RECURSION_WARNING))
eckhart's avatar
eckhart committed
463
                            # error_id = id(node)
464
                            grammar.last_recursion_location__ = location
465
466
467
468
                    # 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
469
                    visited[location] = (None, rest)
470
            else:
471
                # assert node._pos < 0 or node == EMPTY_NODE
472
                # if node._pos != EMPTY_NODE:
473
                node._pos = location
474
475
                # assert node._pos >= 0 or node == EMPTY_NODE, \
                #     str("%i < %i" % (grammar.document_length__, location))
476
477
478
479
480
481
                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
eckhart's avatar
eckhart committed
482
483
                    # TODO: need a unit-test concerning interference of variable manipulation
                    #       and left recursion algorithm?
484
                    visited[location] = (node, rest)
485
486

        except RecursionError:
487
            node = Node(ZOMBIE_TAG, str(text[:min(10, max(1, text.find("\n")))]) + " ...")
488
489
490
491
492
493
            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
494
495
496
497

    def __add__(self, other: 'Parser') -> 'Series':
        """The + operator generates a series-parser that applies two
        parsers in sequence."""
di68kap's avatar
di68kap committed
498
499
        if isinstance(other, Series):
            return cast('Series', other).__radd__(self)
500
501
502
503
504
505
        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.
        """
di68kap's avatar
di68kap committed
506
507
        if isinstance(other, Alternative):
            return cast('Alternative', other).__ror__(self)
508
509
        return Alternative(self, other)

di68kap's avatar
di68kap committed
510
511
512
513
514
515
516
517
518
    def __mul__(self, other: 'Parser') -> 'Alternative':
        """The * operator generates an interleave parser that applies
        the first parser and the second parser in any possible order
        until both match.
        """
        if isinstance(other, Interleave):
            return cast(Interleave, other).__rmul__(self)
        return Interleave(self, other)

519
520
521
522
523
524
    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

525
526
527
528
529
530
531
532
    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:
Eckhart Arnold's avatar
Eckhart Arnold committed
533
            self._parse_proxy = self._parse
534
        else:
eckhart's avatar
eckhart committed
535
536
            if not isinstance(proxy, type(self._parse)):
                # assume that proxy is a function and bind it to self
537
538
                proxy = proxy.__get__(self, type(self))
            else:
eckhart's avatar
eckhart committed
539
                # if proxy is a method it must be a method of self
540
                assert proxy.__self__ == self
Eckhart Arnold's avatar
Eckhart Arnold committed
541
            self._parse_proxy = cast(ParseFunc, proxy)
542

543
    @property
eckhart's avatar
eckhart committed
544
    def grammar(self) -> 'Grammar':
545
546
547
548
549
        try:
            if self._grammar != GRAMMAR_PLACEHOLDER:
                return self._grammar
            else:
                raise AssertionError('Grammar has not yet been set!')
550
551
        except (AttributeError, NameError):
            raise AttributeError('Parser placeholder does not have a grammar!')
552
553
554

    @grammar.setter
    def grammar(self, grammar: 'Grammar'):
555
556
557
558
559
        try:
            if self._grammar == GRAMMAR_PLACEHOLDER:
                self._grammar = grammar
                # self._grammar_assigned_notifier()
            elif self._grammar != grammar:
eckhart's avatar
eckhart committed
560
561
                raise AssertionError("Parser has already been assigned"
                                     "to a different Grammar object!")
562
563
        except AttributeError:
            pass  # ignore setting of grammar attribute for placeholder parser
564
565
        except NameError:  # Cython: No access to GRAMMA_PLACEHOLDER, yet :-(
            self._grammar = grammar
566

eckhart's avatar
eckhart committed
567
    def sub_parsers(self) -> Tuple['Parser', ...]:
568
569
570
        """Returns the list of sub-parsers if there are any.
        Overridden by Unary, Nary and Forward.
        """
eckhart's avatar
eckhart committed
571
        return tuple()
572

573
    def _apply(self, func: ApplyFunc, flag_cycle: FlagFunc) -> bool:
574
575
        """
        Applies function `func(parser)` recursively to this parser and all
576
577
        descendant parsers as long as `func()` returns `None` or `False`.
        Otherwise stops the further application of `func` and returns `True`.
eckhart's avatar
eckhart committed
578
579
580
581
582
583
584
585

        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!
586
        """
587
588
589
590
591
592
593
594
595
        if not flag_cycle(func, self.cycle_detection):
            if func(self):
                return True
            else:
                for parser in self.sub_parsers():
                    if parser._apply(func, flag_cycle):
                        return True
                return False
        return False
596

597
    def apply(self, func: ApplyFunc) -> bool:
eckhart's avatar
eckhart committed
598
599
        """
        Applies function `func(parser)` recursively to this parser and all
600
601
602
603
604
605
606
607
608
609
610
611
612
613
        descendant parsers as long as `func()` returns `None` or `False`.
        Traversal is pre-order. Stops the further application of `func` and
        returns `True` once `func` has returned `True`.

        If `func` has been applied to all descendant parsers without issuing
        a stop signal by returning `True`, `False` is returned.

        This use of the return value allows to use the `apply`-method both
        to issue tests on all descendant parsers (including self) which may be
        decided already after some parsers have been visited without any need
        to visit further parsers. At the same time `apply` can be used to simply
        `apply` a procedure to all descendant parsers (including self) without
        worrying about forgetting the return value of procedure, because a
        return value of `None` means "carry on".
eckhart's avatar
eckhart committed
614
        """
Eckhart Arnold's avatar
Eckhart Arnold committed
615
        def positive_flip(f: Callable[['Parser'], None], flagged: Set[Callable]) -> bool:
eckhart's avatar
eckhart committed
616
617
618
619
620
621
622
623
624
            """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

Eckhart Arnold's avatar
Eckhart Arnold committed
625
        def negative_flip(f: Callable[['Parser'], None], flagged: Set[Callable]) -> bool:
eckhart's avatar
eckhart committed
626
627
628
629
630
631
632
633
634
635
            """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:
636
            return self._apply(func, negative_flip)
eckhart's avatar
eckhart committed
637
        else:
638
639
640
641
642
643
            return self._apply(func, positive_flip)

    def static_analysis(self) -> Optional[List['GrammarErrorType']]:
        """Analyses the parser for logical errors after the grammar has been
        instantiated."""
        return None
eckhart's avatar
eckhart committed
644

645

646
647
def copy_parser_base_attrs(src: Parser, duplicate: Parser):
    """Duplicates all attributes of the Parser-class from source to dest."""
Eckhart Arnold's avatar
Eckhart Arnold committed
648
649
650
651
652
653
    duplicate.pname = src.pname
    duplicate.anonymous = src.anonymous
    duplicate.drop_content = src.drop_content
    duplicate.tag_name = src.tag_name


eckhart's avatar
eckhart committed
654
655
def Drop(parser: Parser) -> Parser:
    """Returns the parser with the `parser.drop_content`-property set to `True`."""
Eckhart Arnold's avatar
Eckhart Arnold committed
656
    assert parser.anonymous, "Parser must be anonymous to be allowed to drop ist content."
eckhart's avatar
eckhart committed
657
658
659
    if isinstance(parser, Forward):
        cast(Forward, parser).parser.drop_content = True
    parser.drop_content = True
Eckhart Arnold's avatar
Eckhart Arnold committed
660
    return parser
eckhart's avatar
eckhart committed
661
662


663
PARSER_PLACEHOLDER = Parser()
664
665


eckhart's avatar
eckhart committed
666
667
668
669
670
def is_parser_placeholder(parser: Optional[Parser]) -> bool:
    """Returns True, if `parser` is `None` or merely a placeholder for a parser."""
    return not parser or parser.ptype == ":Parser"


671
672
673
674
675
676
########################################################################
#
# Grammar class, central administration of all parser of a grammar
#
########################################################################

677
678
def mixin_comment(whitespace: str, comment: str) -> str:
    """
679
    Returns a regular expression pattern that merges comment and whitespace
680
    regexps. Thus comments can occur wherever whitespace is allowed
681
682
683
684
685
686
    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).
    """
687
688
689
    if comment:
        return '(?:' + whitespace + '(?:' + comment + whitespace + ')*)'
    return whitespace
690
691


di68kap's avatar
di68kap committed
692
def mixin_nonempty(whitespace: str) -> str:
Eckhart Arnold's avatar
Eckhart Arnold committed
693
    r"""
694
695
696
    Returns a regular expression pattern that matches only if the regular
    expression pattern `whitespace` matches AND if the match is not empty.

di68kap's avatar
di68kap committed
697
698
    If `whitespace`  does not match the empty string '', anyway,
    then it will be returned unaltered.
699
700
701
702
703
704
705
706
707

    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
708
709
710
711
712
    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".
713
714
715
716
717
718
719
720
721
722

    :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


723
class UnknownParserError(KeyError):
eckhart's avatar
eckhart committed
724
    """UnknownParserError is raised if a Grammar object is called with a
725
    parser that does not exist or if in the course of parsing a parser
eckhart's avatar
eckhart committed
726
    is referred to that does not exist."""
727
728


729
GrammarErrorType = Tuple[str, Parser, Error]      # TODO: replace with a named tuple?
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746


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))


747
748
749
750
751
752
753
754
755
756
757
758
759
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
760
    Example for direct instantiation of a grammar::
761

762
        >>> number = RE(r'\d+') + RE(r'\.') + RE(r'\d+') | RE(r'\d+')
763
764
765
766
767
768
769
770
771
772
773
774
775
776
        >>> 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.
777
       See classmethod `Grammar._assign_parser_names__()`
778
779

    3. The parsers in the class do not necessarily need to be connected
780
781
       to one single root parser, which is helpful for testing and when
       building up a parser gradually from several components.
782
783
784
785
786
787
788

    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.

789
    Example::
790
791
792
793
794
795
796
797
798

        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+')
799
800
801
            factor = INTEGER | TKN("(") + expression + TKN(")")
            term = factor + ZeroOrMore((TKN("*") | TKN("/")) + factor)
            expression.set(term + ZeroOrMore((TKN("+") | TKN("-")) + term))
802
803
804
805
            root__ = expression

    Upon instantiation the parser objects are deep-copied to the
    Grammar object and assigned to object variables of the same name.
806
807
808
809
810
    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.
811
    If one and the same parser is assigned to several class variables
812
    such as, for example, the parser `expression` in the example above,
813
    which is also assigned to `root__`, the first name sticks.
814
815
816
817
818
819
820
821
822
823
824
825

    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:

826
    Class Attributes:
827
828
829
830
        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.
831

832
833
834
        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
835

836
837
838
839
840
        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
841
842
                parsers that are not directly assigned to a class field.

eckhart's avatar
eckhart committed
843
        parser_initialization__:  Before the grammar class (!) has been initialized,
844
                 which happens upon the first time it is instantiated (see
845
                 `:func:_assign_parser_names()` for an explanation), this class
846
847
                 field contains a value other than "done". A value of "done" indicates
                 that the class has already been initialized.
848

849
850
851
852
853
854
855
        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.
856

eckhart's avatar
eckhart committed
857
858
859
860
        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`).

861
    Instance Attributes:
862
863
        all_parsers__:  A set of all parsers connected to this grammar object

864
865
        comment_rx__:  The compiled regular expression for comments. If no
                comments have been defined, it defaults to RX_NEVER_MATCH
866
867
                This instance-attribute will only be defined if a class-attribute
                with the same name does not already exist!
868

eckhart's avatar
eckhart committed
869
870
871
872
        start_parser__:  During parsing, the parser with which the parsing process
                was started (see method `__call__`) or `None` if no parsing process
                is running.

873
874
875
876
877
878
879
        _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
880
881
        document_length__:  the length of the document.

882
883
        document_lbreaks__ (property):  list of linebreaks within the document,
                starting with -1 and ending with EOF. This helps generating line
884
                and column number for history recording and will only be
885
                initialized if :attr:`history_tracking__` is true.
886

887
888
889
890
891
        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.

892
        _reversed__:  the same text in reverse order - needed by the `Lookbehind`-
893
894
895
                parsers.

        variables__:  A mapping for variable names to a stack of their respective
896
897
                string values - needed by the :class:`Capture`-, :class:`Retrieve`-
                and :class:`Pop`-parsers.
898
899

        rollback__:  A list of tuples (location, rollback-function) that are
900
901
902
903
                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.
904
905
906

        last_rb__loc__:  The last, i.e. most advanced location in the text
                where a variable changing operation occurred. If the parser
907
908
                backtracks to a location at or before last_rb__loc__ (i.e.
                location <= last_rb__loc__) then a rollback of all variable
909
910
                changing operations is necessary that occurred after the
                location to which the parser backtracks. This is done by
911
                calling method :func:`rollback_to__(location)`.
912

913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
        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
                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.

        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)


        # tracing and debugging support

        # These parameters are needed by the debugging functions in module
        # `trace.py`. They should not be manipulated by the users of class
        #  Grammar directly.

        history_tracking__:  A flag indicating that the parsing history is
                being tracked. This flag should not be manipulated by the
                user. Use `trace.set_tracer(grammar, trace.trace_history)` to
                turn (full) history tracking on and
                `trace.set_tracer(grammar, None)` to turn it off. Default is off.

        resume_notices__: A flag indicating that resume messages are generated
                in addition to the error messages, in case the parser was able
                to resume after an error. Use `trace.resume_notices(grammar)` to
                turn resume messages on and `trace.set_tracer(grammar, None)`
                to turn resume messages (as well as history recording) off.
                Default is off.

di68kap's avatar
di68kap committed
947
948
949
        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.
950
                This is required for recording the parser history (for debugging)
951
952
953
                and, eventually, i.e. one day in the future, for tracing through
                the parsing process.

954
955
956
957
        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.
958
959
960
961

        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
962
                recording is turned off! (See :func:`Parser.__call__`)
963

964
965
966
        most_recent_error__: The most recent parser error that has occurred
                or `None`. This can be read by tracers. See module `trace`

967

968
969
970
971
        # Configuration parameters.

        # These values of theses parameters are copied from the global configuration
        # in the constructor of the Grammar object. (see mpodule `configuration.py`)
972

973
974
975
        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.
976
                Default is on.
977
978
979

        left_recursion_depth__: the maximum allowed depth for left-recursion.
                A depth of zero means that no left recursion handling will
980
                take place. Default is 5.
981
982
983

        max_parser_dropouts__: Maximum allowed number of retries after errors
                where the parser would exit before the complete document has
984
985
                been parsed. Default is 1, as usually the retry-attemts lead
                to a proliferation of senseless error messages.
986
987
988

        reentry_search_window__: The number of following characters that the
                parser considers when searching a reentry point when a syntax error
989
                has been encountered. Default is 10.000 characters.
990
    """
eckhart's avatar
eckhart committed
991
    python_src__ = ''  # type: str
992
    root__ = PARSER_PLACEHOLDER  # type: Parser
993
    # root__ must be overwritten with the root-parser by grammar subclass
eckhart's avatar
eckhart committed
994
    parser_initialization__ = ["pending"]  # type: List[str]
eckhart's avatar
eckhart committed
995
    resume_rules__ = dict()  # type: Dict[str, ResumeList]
996
    anonymous__ = RX_NEVER_MATCH  # type: RxPatternType
997
    # some default values
eckhart's avatar
eckhart committed
998
999
    COMMENT__ = r''  # type: str  # r'#.*(?:\n|$)'
    WSP_RE__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)  # type: str
1000
    static_analysis_pending__ = [True]  # type: List[bool]