2.12.2021, 9:00 - 11:00: Due to updates GitLab may be unavailable for some minutes between 09:00 and 11:00.

parser.py 75.1 KB
Newer Older
1
"""parsers.py - parser combinators for 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
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46

Module ``parsers.py`` contains a number of classes that together
make up parser combinators for left-recursive grammers. For each
element of the extended Backus-Naur-Form as well as for a regular
expression token a class is defined. The set of classes can be used to
define a parser for (ambiguous) left-recursive grammers.


References and Acknowledgements:

Dominikus Herzberg: Objekt-orientierte Parser-Kombinatoren in Python,
Blog-Post, September, 18th 2008 on denkspuren. gedanken, ideen,
anregungen und links rund um informatik-themen, URL:
http://denkspuren.blogspot.de/2008/09/objekt-orientierte-parser-kombinatoren.html

Dominikus Herzberg: Eine einfache Grammatik für LaTeX, Blog-Post,
September, 18th 2008 on denkspuren. gedanken, ideen, anregungen und
links rund um informatik-themen, URL:
http://denkspuren.blogspot.de/2008/09/eine-einfache-grammatik-fr-latex.html

Dominikus Herzberg: Uniform Syntax, Blog-Post, February, 27th 2007 on
denkspuren. gedanken, ideen, anregungen und links rund um
informatik-themen, URL:
http://denkspuren.blogspot.de/2007/02/uniform-syntax.html

Richard A. Frost, Rahmatullah Hafiz and Paul Callaghan: Parser
Combinators for Ambiguous Left-Recursive Grammars, in: P. Hudak and
D.S. Warren (Eds.): PADL 2008, LNCS 4902, pp. 167–181, Springer-Verlag
Berlin Heidelberg 2008.

47
48
49
50
Elizabeth Scott and Adrian Johnstone, GLL Parsing,
in: Electronic Notes in Theoretical Computer Science 253 (2010) 177–189,
http://dotat.at/tmp/gll.pdf

Eckhart Arnold's avatar
Eckhart Arnold committed
51
52
Juancarlo Añez: grako, a PEG parser generator in Python,
https://bitbucket.org/apalala/grako
53
54
55

Vegard Øye: General Parser Combinators in Racket, 2012,
https://epsil.github.io/gll/
56
57
"""

58

Eckhart Arnold's avatar
Eckhart Arnold committed
59
import abc
60
import copy
61
import os
Eckhart Arnold's avatar
Eckhart Arnold committed
62
63
from functools import partial

64
65
66
67
try:
    import regex as re
except ImportError:
    import re
68
try:
69
    from typing import Any, Callable, cast, Dict, Iterator, List, Set, Tuple, Union, Optional
70
71
72
73
    # try:
    #     from typing import Collection
    # except ImportError:
    #     pass
74
except ImportError:
75
    from .typing34 import Any, Callable, cast, Dict, Iterator, List, Set, Tuple, Union, Optional
76

77
from DHParser.toolkit import is_logging, log_dir, logfile_basename, escape_re, sane_parser_name
Eckhart Arnold's avatar
Eckhart Arnold committed
78
79
from DHParser.syntaxtree import WHITESPACE_PTYPE, TOKEN_PTYPE, ZOMBIE_PARSER, ParserBase, \
    Node, TransformationFunc
80
from DHParser.toolkit import load_if_file, error_messages, line_col
Eckhart Arnold's avatar
Eckhart Arnold committed
81

82
__all__ = ('PreprocessorFunc',
83
           'HistoryRecord',
Eckhart Arnold's avatar
Eckhart Arnold committed
84
           'Parser',
85
           'Grammar',
86
87
88
           'RX_PREPROCESSOR_TOKEN',
           'BEGIN_TOKEN',
           'END_TOKEN',
Eckhart Arnold's avatar
Eckhart Arnold committed
89
           'make_token',
90
91
           'nil_preprocessor',
           'PreprocessorToken',
Eckhart Arnold's avatar
Eckhart Arnold committed
92
93
94
95
           'RegExp',
           'RE',
           'Token',
           'mixin_comment',
96
97
98
           # 'UnaryOperator',
           # 'NaryOperator',
           'Synonym',
Eckhart Arnold's avatar
Eckhart Arnold committed
99
100
101
           'Optional',
           'ZeroOrMore',
           'OneOrMore',
102
           'Series',
Eckhart Arnold's avatar
Eckhart Arnold committed
103
104
105
106
107
108
109
           'Alternative',
           'FlowOperator',
           'Required',
           'Lookahead',
           'NegativeLookahead',
           'Lookbehind',
           'NegativeLookbehind',
110
111
112
           'last_value',
           'counterpart',
           'accumulate',
Eckhart Arnold's avatar
Eckhart Arnold committed
113
114
115
116
           'Capture',
           'Retrieve',
           'Pop',
           'Forward',
117
           'Compiler',
118
           'compile_source')
Eckhart Arnold's avatar
Eckhart Arnold committed
119

120

121

122
123
124
125
126
127
128
########################################################################
#
# Grammar and parsing infrastructure
#
########################################################################


129
PreprocessorFunc = Union[Callable[[str], str], partial]
130
131


132
133
134
LEFT_RECURSION_DEPTH = 8  # type: int
# because of python's recursion depth limit, this value ought not to be
# set too high. PyPy allows higher values than CPython
Eckhart Arnold's avatar
Eckhart Arnold committed
135
MAX_DROPOUTS = 3  # type: int
136
# stop trying to recover parsing after so many errors
137

138

139
140
141
142
143
144
145
146
147
148
149
150
151
class HistoryRecord:
    """
    Stores debugging information about one completed step in the
    parsing history. 

    A parsing step is "completed" when the last one of a nested
    sequence of parser-calls returns. The call stack including
    the last parser call will be frozen in the ``HistoryRecord``-
    object. In addition a reference to the generated leaf node
    (if any) will be stored and the result status of the last
    parser call, which ist either MATCH, FAIL (i.e. no match)
    or ERROR.
    """
152
    __slots__ = ('call_stack', 'node', 'remaining', 'line_col')
153
154
155
156
157

    MATCH = "MATCH"
    ERROR = "ERROR"
    FAIL = "FAIL"

158
    def __init__(self, call_stack: List['Parser'], node: Node, remaining: int) -> None:
159
160
161
        # copy call stack, dropping uninformative Forward-Parsers
        self.call_stack = [p for p in call_stack if p.ptype != ":Forward"]
        # type: List['Parser']
162
163
        self.node = node                # type: Node
        self.remaining = remaining      # type: int
164
165
166
167
168
169
        document = call_stack[-1].grammar.document__ if call_stack else ''
        self.line_col = line_col(document, len(document) - remaining)  # type: Tuple[int, int]

    def __str__(self):
        return 'line %i, column %i:  %s  "%s"' % \
               (self.line_col[0], self.line_col[1], self.stack, str(self.node))
170

171
    def err_msg(self) -> str:
172
173
        return self.ERROR + ": " + "; ".join(self.node._errors).replace('\n', '\\')

174
    @property
175
    def stack(self) -> str:
176
        return "->".join((p.repr if p.ptype == ':RegExp' else p.name or p.ptype)
177
                         for p in self.call_stack)
178
179

    @property
180
    def status(self) -> str:
181
182
        return self.FAIL if self.node is None else \
            self.err_msg() if self.node._errors else self.MATCH
183
184

    @property
185
186
187
    def extent(self) -> slice:
        return (slice(-self.remaining - self.node.len, -self.remaining) if self.node
                else slice(-self.remaining, None))
188

189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
    @staticmethod
    def last_match(history: List['HistoryRecord']) -> Optional['HistoryRecord']:
        """
        Returns the last match from the parsing-history.
        Args:
            history:  the parsing-history as a list of HistoryRecord objects

        Returns:
            the history record of the last match or none if either history is
            empty or no parser could match
        """
        for record in reversed(history):
            if record.status == HistoryRecord.MATCH:
                return record
        return None

    @staticmethod
    def most_advanced_match(history: List['HistoryRecord']) -> Optional['HistoryRecord']:
        """
        Returns the closest-to-the-end-match from the parsing-history.
        Args:
            history:  the parsing-history as a list of HistoryRecord objects

        Returns:
            the history record of the closest-to-the-end-match or none if either history is
            empty or no parser could match
        """
        remaining = -1
        result = None
        for record in history:
            if (record.status == HistoryRecord.MATCH and
                    (record.remaining < remaining or remaining < 0)):
                result = record
                remaining = record.remaining
        return result


226
def add_parser_guard(parser_func):
227
228
229
230
231
    """
    Add a wrapper function to a parser functions (i.e. Parser.__call__ method)
    that takes care of memoizing, left recursion and optionally tracing
    (aka "history tracking") of parser calls. Returns the wrapped call.
    """
232
    def guarded_call(parser: 'Parser', text: str) -> Tuple[Node, str]:
233
234
235
236
237
238
        def memoized(parser, location):
            node = parser.visited[location]
            rlen = location - (0 if node is None else node.len)
            rest = grammar.document__[-rlen:] if rlen else ''
            return node, rest

239
        try:
240
            location = len(text)    # mind that location is always the distance to the end
241
242
            grammar = parser.grammar  # grammar may be 'None' for unconnected parsers!

243
244
            if grammar.last_rb__loc__ <= location:
                grammar.rollback_to__(location)
245

246
247
248
            # if location has already been visited by the current parser,
            # return saved result
            if location in parser.visited:
249
                return memoized(parser, location)
250

251
252
            # break left recursion at the maximum allowed depth
            if parser.recursion_counter.setdefault(location, 0) > LEFT_RECURSION_DEPTH:
253
                grammar.recursion_locations__.add(location)
254
255
                return None, text

Eckhart Arnold's avatar
Eckhart Arnold committed
256
257
            if grammar.history_tracking__:
                grammar.call_stack__.append(parser)
258
                grammar.moving_forward__ = True
Eckhart Arnold's avatar
Eckhart Arnold committed
259

260
261
262
263
264
            parser.recursion_counter[location] += 1

            # run original __call__ method
            node, rest = parser_func(parser, text)

265
            if node is None:
266
                # retrieve an earlier match result (from left recursion) if it exists
267
268
269
270
271
272
                if location in grammar.recursion_locations__:
                    if location in parser.visited:
                        node, rest = memoized(parser, location)
                    # 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__:
273
                    # otherwise also cache None-results
274
                    parser.visited[location] = None
275
276
277
278
279
280
281
            elif ((grammar.memoization__ or location in grammar.recursion_locations__)
                  and grammar.last_rb__loc__ > location):
                # - 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
                parser.visited[location] = node
282
283
284

            parser.recursion_counter[location] -= 1

285
            if grammar.history_tracking__:
286
                # don't track returning parsers except in case an error has occurred
287
                remaining = len(rest)
288
                if grammar.moving_forward__ or (node and node._errors):
289
                    record = HistoryRecord(grammar.call_stack__, node, remaining)
290
                    grammar.history__.append(record)
291
                    # print(record.stack, record.status, rest[:20].replace('\n', '|'))
292
                grammar.moving_forward__ = False
293
                grammar.call_stack__.pop()
294

295
296
297
298
299
300
301
302
303
304
305
        except RecursionError:
            node = Node(None, text[:min(10, max(1, text.find("\n")))] + " ...")
            node.add_error("maximum recursion depth of parser reached; "
                           "potentially due to too many errors!")
            rest = ''

        return node, rest

    return guarded_call


Eckhart Arnold's avatar
Eckhart Arnold committed
306
class ParserMetaClass(abc.ABCMeta):
307
308
309
310
311
    """
    ParserMetaClass adds a wrapper to the __call__ method of parser
    objects during initialization that takes care of memoizing,
    left recursion and tracing.
    """
312
    def __init__(cls, name, bases, attrs):
313
314
        guarded_parser_call = add_parser_guard(cls.__call__)
        # The following check is necessary for classes that don't override
315
316
317
318
319
320
321
        # the __call__() method, because in these cases the non-overridden
        # __call__()-method would be substituted a second time!
        if cls.__call__.__code__ != guarded_parser_call.__code__:
            cls.__call__ = guarded_parser_call
        super(ParserMetaClass, cls).__init__(name, bases, attrs)


Eckhart Arnold's avatar
Eckhart Arnold committed
322
class Parser(ParserBase, metaclass=ParserMetaClass):
323
324
325
326
    """
    (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.
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343

    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:

    1. *Named parsers* for which a name is set in field parser.name.
       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.
Eckhart Arnold's avatar
Eckhart Arnold committed
344
345

    Parser objects are callable and parsing is done by calling a parser
Eckhart Arnold's avatar
Eckhart Arnold committed
346
347
348
349
350
351
352
353
354
355
356
357
358
    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 `Optional`). 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.
359
360

    Attributes:
361
362
        visited:  Mapping of places this parser has already been to
                during the current parsing process onto the node the
363
364
365
366
367
368
369
370
                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.

371
        cycle_detection:  The apply()-method uses this variable to make
372
373
374
                sure that one and the same function will not be applied
                (recursively) a second time, if it has already been
                applied to this parser.
375
376
377

        grammar:  A reference to the Grammar object to which the parser
                is attached.
378
379
    """

380
381
    ApplyFunc = Callable[['Parser'], None]

382
383
    def __init__(self, name: str = '') -> None:
        # assert isinstance(name, str), str(name)
Eckhart Arnold's avatar
Eckhart Arnold committed
384
        super(Parser, self).__init__(name)
385
        self._grammar = None  # type: 'Grammar'
386
387
        self.reset()

Eckhart Arnold's avatar
Eckhart Arnold committed
388
    def __deepcopy__(self, memo):
Eckhart Arnold's avatar
Eckhart Arnold committed
389
390
391
392
393
394
        """Deepcopy method of the parser. Upon instantiation of a Grammar-
        object, parsers will be deep-copied to the Grammar object. If a
        derived parser-class changes the signature of the constructor,
        `__deepcopy__`-method must be replaced (i.e. overridden without
        calling the same method from the superclass) by the derived class.
        """
395
396
        return self.__class__(self.name)

397
    def reset(self):
Eckhart Arnold's avatar
Eckhart Arnold committed
398
399
400
        """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."""
401
        self.visited = dict()            # type: Dict[int, Node]
402
        self.recursion_counter = dict()  # type: Dict[int, int]
403
        self.cycle_detection = set()     # type: Set[Callable]
404
        return self
405

406
    def __call__(self, text: str) -> Tuple[Node, str]:
Eckhart Arnold's avatar
Eckhart Arnold committed
407
408
409
        """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."""
410
411
        return None, text  # default behaviour: don't match

412
    def __add__(self, other: 'Parser') -> 'Series':
413
414
        """The + operator generates a series-parser that applies two
        parsers in sequence."""
415
        return Series(self, other)
416

417
    def __or__(self, other: 'Parser') -> 'Alternative':
418
419
420
        """The | operator generates an alternative parser that applies
        the first parser and, if that does not match, the second parser.
        """
421
422
        return Alternative(self, other)

423
    @property
424
    def grammar(self) -> 'Grammar':
425
426
427
        return self._grammar

    @grammar.setter
428
    def grammar(self, grammar: 'Grammar'):
Eckhart Arnold's avatar
Eckhart Arnold committed
429
430
431
432
433
434
        if self._grammar is None:
            self._grammar = grammar
            self._grammar_assigned_notifier()
        else:
            assert self._grammar == grammar, \
                "Parser has already been assigned to a different Grammar object!"
435
436

    def _grammar_assigned_notifier(self):
437
438
        """A function that notifies the parser object that it has been
        assigned to a grammar."""
439
440
        pass

441
    def apply(self, func: ApplyFunc):
442
443
        """
        Applies function `func(parser)` recursively to this parser and all
Eckhart Arnold's avatar
Eckhart Arnold committed
444
        descendant parsers if any exist. The same function can never
445
446
447
448
449
450
451
452
453
454
        be applied twice between calls of the ``reset()``-method!
        """
        if func in self.cycle_detection:
            return False
        else:
            self.cycle_detection.add(func)
            func(self)
            return True


455
def mixin_comment(whitespace: str, comment: str) -> str:
456
457
    """
    Returns a regular expression that merges comment and whitespace
458
459
460
461
462
463
464
465
466
467
468
    regexps. Thus comments cann occur whereever whitespace is allowed
    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).
    """
    wspc = '(?:' + whitespace + '(?:' + comment + whitespace + ')*)'
    return wspc


469
class Grammar:
470
    """
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
    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.

    Example for direct instantian of a grammar:

        >>> number = RE('\d+') + RE('\.') + RE('\d+') | RE('\d+')
        >>> number_parser = Grammar(number)
Eckhart Arnold's avatar
Eckhart Arnold committed
486
        >>> number_parser("3.1416").content()
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
        '3.1416'

    Collecting the parsers that define a grammar in a descentand 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.

    3. The parsers in class do not necessarily need to be connected to one
       single root parser, which is helpful for testing and building up a
       parser successively of several components.

    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.
508
509

    Example:
510

511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
        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+')
            factor = INTEGER | Token("(") + expression + Token(")")
            term = factor + ZeroOrMore((Token("*") | Token("/")) + factor)
            expression.set(term + ZeroOrMore((Token("+") | Token("-")) + term))
            root__ = expression

    Upon instantiation the parser objects are deep-copied to the
    Grammar object and assigned to object variables of the same name.
    Any parser that is directly assigned to a class variable is a
    'named' parser and its field `parser.name` contains the variable
    name after instantiation of the Grammar class. All other parsers,
529
530
531
    i.e. parsers that are defined within a `named` parser, remain
    "anonymous parsers" where `parser.name` is the empty string, unless
    a name has been passed explicitly upon instantiation.
532
533
534
535
536
537
538
539
540
541
542
    If one and the same parser is assigned to several class variables
    such as, for example the parser `expression` in the example above,
    the first name sticks.

    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.

543
    Grammar classes contain a few special class fields for implicit
544
545
    whitespace and comments that should be overwritten, if the defaults
    (no comments, horizontal right aligned whitespace) don't fit:
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
    COMMENT__:  regular expression string for matching comments
    WSP__:   regular expression for whitespace and comments
    wspL__:  regular expression string for left aligned whitespace,
             which either equals WSP__ or is empty.
    wspR__:  regular expression string for right aligned whitespace,
             which either equals WSP__ or is empty.
    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.
    parser_initializiation__:  Before the parser class (!) has been initialized,
             which happens upon the first time it is instantiated (see doctring for
             method `_assign_parser_names()` for an explanation), this class
             field contains a value other than "done". A value of "done" indicates
             that the class has already been initialized.

    Attributes:
        all_parsers__:  A set of all parsers connected to this grammar object

565
        hostory_tracking__:  A flag indicating that the parsing history shall
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
                be tracked

        wsp_left_parser__:  A parser for the default left-adjacent-whitespace
                or the zombie-parser (see `syntaxtree.ZOMBIE_PARSER`) if the
                default is empty. The default whitespace will be used by parsers
                `Token` and, if no other parsers are passed to its constructor,
                by parser `RE'.
        wsp_right_parser__: The same for the default right-adjacent-whitespace.
                Both wsp_left_parser__ and wsp_right_parser__ merely serve the
                purpose to avoid having to specify the default whitespace
                explicitly every time an `RE`-parser-object is created.

        _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.
        _reversed__:  the same text in reverse order - needed by the `Lookbehind'-
                parsers.
        variables__:  A mapping for variable names to a stack of their respective
                string values - needed by the `Capture`-, `Retrieve`- and `Pop`-
                parsers.
        rollback__:  A list of tuples (location, rollback-function) that are
                deposited by the `Capture`- and `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.
594
595
596
597
598
599
600
601
        last_rb__loc__:  The last, i.e. most advanced location in the text
                where a variable changing operation occurred. If the parser
                backtracks to a location at or before `last_rb__loc__` (which,
                since locations are counted from the reverse, means:
                `location >= last_rb__loc__`) then a rollback of all variable
                changing operations is necessary that occurred after the
                location to which the parser backtracks. This is done by
                calling method `.rollback_to__(location)`.
602
603
604
605
606
607
608
        call_stack__:  A stack of all parsers that have been called. This
                is required for recording the parser history (for debugging)
                and, eventually, i.e. one day in the future, for tracing through
                the parsing process.
        history__:  A list of parser-call-stacks. A parser-call-stack is
                appended to the list each time a parser either matches, fails
                or if a parser-error occurs.
609
610
611
612
613
614
615
616
617
618
        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
                recording is turned off! (See `add_parser_guard` and its local
                function `guarded_call`)
        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 `add_parser_guard` and its
                local function `guarded_call`)
619
620
621
622
        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.
623
    """
624
625
    root__ = None  # type: Union[Parser, None]
    # root__ must be overwritten with the root-parser by grammar subclass
Eckhart Arnold's avatar
Eckhart Arnold committed
626
    parser_initialization__ = "pending"  # type: str
627
628
629
630
631
    # some default values
    COMMENT__ = r''  # r'#.*(?:\n|$)'
    WSP__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)
    wspL__ = ''
    wspR__ = WSP__
632

633

634
    @classmethod
635
    def _assign_parser_names__(cls):
636
637
        """
        Initializes the `parser.name` fields of those
638
639
        Parser objects that are directly assigned to a class field with
        the field's name, e.g.
640
            class Grammar(Grammar):
641
642
643
                ...
                symbol = RE('(?!\\d)\\w+')
        After the call of this method symbol.name == "symbol"
644
645
646
647
        holds. Names assigned via the ``name``-parameter of the
        constructor will not be overwritten. Parser names starting or
        ending with a double underscore like ``root__`` will be
        ignored. See ``toolkit.sane_parser_name()``
648
649
650
651

        This is done only once, upon the first instantiation of the
        grammar class!

652
653
654
655
656
        Attention: If there exists more than one reference to the same
        parser, only the first one will be chosen for python versions 
        greater or equal 3.6.  For python version <= 3.5 an arbitrarily
        selected reference will be chosen. See PEP 520
        (www.python.org/dev/peps/pep-0520/) for an explanation of why. 
657
        """
658
659
660
661
662
663
664
665
666
        if cls.parser_initialization__ != "done":
            cdict = cls.__dict__
            for entry, parser in cdict.items():
                if isinstance(parser, Parser) and sane_parser_name(entry):
                    if not parser.name:
                        parser.name = entry
                    if (isinstance(parser, Forward) and (not parser.parser.name)):
                        parser.parser.name = entry
            cls.parser_initialization__ = "done"
667

668

Eckhart Arnold's avatar
Eckhart Arnold committed
669
670
671
    def __init__(self, root: Parser=None) -> None:
        # if not hasattr(self.__class__, 'parser_initialization__'):
        #     self.__class__.parser_initialization__ = "pending"
672
673
674
675
        # if not hasattr(self.__class__, 'wspL__'):
        #     self.wspL__ = ''
        # if not hasattr(self.__class__, 'wspR__'):
        #     self.wspR__ = ''
676
        self.all_parsers__ = set()  # type: Set[Parser]
677
678
        self._dirty_flag__ = False  # type: bool
        self.history_tracking__ = False  # type: bool
679
        self.memoization__ = True  # type: bool
680
        self._reset__()
681

Eckhart Arnold's avatar
Eckhart Arnold committed
682
        # prepare parsers in the class, first
683
        self._assign_parser_names__()
684

Eckhart Arnold's avatar
Eckhart Arnold committed
685
686
687
688
        # then deep-copy the parser tree from class to instance;
        # parsers not connected to the root object will be copied later
        # on demand (see Grammar.__getitem__()). Usually, the need to
        # do so only arises during testing.
Eckhart Arnold's avatar
Eckhart Arnold committed
689
        self.root__ = copy.deepcopy(root) if root else copy.deepcopy(self.__class__.root__)
690

691
        if self.wspL__:
Eckhart Arnold's avatar
Eckhart Arnold committed
692
            self.wsp_left_parser__ = Whitespace(self.wspL__)  # type: ParserBase
693
            self.wsp_left_parser__.grammar = self
694
            self.all_parsers__.add(self.wsp_left_parser__)  # don't you forget about me...
695
696
697
        else:
            self.wsp_left_parser__ = ZOMBIE_PARSER
        if self.wspR__:
Eckhart Arnold's avatar
Eckhart Arnold committed
698
            self.wsp_right_parser__ = Whitespace(self.wspR__)  # type: ParserBase
699
            self.wsp_right_parser__.grammar = self
700
            self.all_parsers__.add(self.wsp_right_parser__)  # don't you forget about me...
701
702
        else:
            self.wsp_right_parser__ = ZOMBIE_PARSER
703
        self.root__.apply(self._add_parser__)
704

705

706
    def __getitem__(self, key):
707
708
709
        try:
            return self.__dict__[key]
        except KeyError:
710
711
            parser_template = getattr(self, key, None)
            if parser_template:
Eckhart Arnold's avatar
Eckhart Arnold committed
712
                # add parser to grammar object on the fly...
713
                parser = copy.deepcopy(parser_template)
714
                parser.apply(self._add_parser__)
715
                # assert self[key] == parser
Eckhart Arnold's avatar
Eckhart Arnold committed
716
                return self[key]
717
            raise KeyError('Unknown parser "%s" !' % key)
718

719

720
    def _reset__(self):
721
        self.document__ = ""          # type: str
Eckhart Arnold's avatar
Eckhart Arnold committed
722
        self._reversed__ = ""         # type: str
723
        # variables stored and recalled by Capture and Retrieve parsers
724
725
        self.variables__ = dict()     # type: Dict[str, List[str]]
        self.rollback__ = []          # type: List[Tuple[int, Callable]]
726
        self.last_rb__loc__ = -1  # type: int
727
        # support for call stack tracing
728
        self.call_stack__ = []        # type: List[Parser]
729
        # snapshots of call stacks
730
        self.history__ = []           # type: List[HistoryRecord]
731
        # also needed for call stack tracing
732
733
        self.moving_forward__ = False  # type: bool
        self.recursion_locations__ = set()  # type: Set[int]
734

735

Eckhart Arnold's avatar
Eckhart Arnold committed
736
737
738
739
740
741
742
    @property
    def reversed__(self) -> str:
        if not self._reversed__:
            self._reversed__ = self.document__[::-1]
        return self._reversed__


743
    def _add_parser__(self, parser: Parser) -> None:
744
745
        """
        Adds the particular copy of the parser object to this
746
        particular instance of Grammar.
747
        """
748
        if parser.name:
Eckhart Arnold's avatar
Eckhart Arnold committed
749
750
751
            # prevent overwriting instance variables or parsers of a different class
            assert parser.name not in self.__dict__ or \
                   isinstance(self.__dict__[parser.name], parser.__class__), \
752
753
                ('Cannot add parser "%s" because a field with the same name '
                 'already exists in grammar object!' % parser.name)
754
            setattr(self, parser.name, parser)
755
        self.all_parsers__.add(parser)
756
757
        parser.grammar = self

758

Eckhart Arnold's avatar
Eckhart Arnold committed
759
    def __call__(self, document: str, start_parser="root__") -> Node:
760
761
        """
        Parses a document with with parser-combinators.
762
763
764

        Args:
            document (str): The source text to be parsed.
765
766
767
            start_parser (str): The name of the parser with which to
                start. This is useful for testing particular parsers
                (i.e. particular parts of the EBNF-Grammar.)
768
769
770
        Returns:
            Node: The root node ot the parse tree.
        """
771
        # assert isinstance(document, str), type(document)
772
773
        if self.root__ is None:
            raise NotImplementedError()
774
        if self._dirty_flag__:
775
            self._reset__()
776
            for parser in self.all_parsers__:
777
778
                parser.reset()
        else:
779
            self._dirty_flag__ = True
780
781
        self.history_tracking__ = is_logging()
        self.document__ = document
782
        self.last_rb__loc__ = len(document) + 1  # rollback location
Eckhart Arnold's avatar
Eckhart Arnold committed
783
        parser = self[start_parser] if isinstance(start_parser, str) else start_parser
784
785
        assert parser.grammar == self, "Cannot run parsers from a different grammar object!" \
                                       " %s vs. %s" % (str(self), str(parser.grammar))
786
        stitches = []  # type: List[Node]
787
        rest = document
788
789
        if not rest:
            result, ignore = parser(rest)
di68kap's avatar
di68kap committed
790
791
792
            if result is None:
                result = Node(None, '')
                result.add_error('Parser "%s" did not match empty document.' % str(parser))
793
794
795
796
797
798
        while rest and len(stitches) < MAX_DROPOUTS:
            result, rest = parser(rest)
            if rest:
                fwd = rest.find("\n") + 1 or len(rest)
                skip, rest = rest[:fwd], rest[fwd:]
                if result is None:
799
800
801
802
                    error_msg = 'Parser did not match! Invalid source file?' \
                                '\n    Most advanced: %s\n    Last match:    %s;' % \
                                (str(HistoryRecord.most_advanced_match(self.history__)),
                                 str(HistoryRecord.last_match(self.history__)))
803
804
805
                else:
                    stitches.append(result)
                    error_msg = "Parser stopped before end" + \
806
807
                                (("! trying to recover" +
                                  (" but stopping history recording at this point."
808
                                   if self.history_tracking__ else "..."))
809
810
811
812
                                 if len(stitches) < MAX_DROPOUTS
                                 else " too often! Terminating parser.")
                stitches.append(Node(None, skip))
                stitches[-1].add_error(error_msg)
813
                if self.history_tracking__:
814
815
816
817
                    # some parsers may have matched and left history records with nodes != None.
                    # Because these are not connected to the stiched root node, their pos
                    # properties will not be initialized by setting the root node's pos property
                    # to zero. Therefore, their pos properties need to be initialized here
818
                    for record in self.history__:
819
820
                        if record.node and record.node._pos < 0:
                            record.node.pos = 0
821
822
823
                    record = HistoryRecord(self.call_stack__.copy(), stitches[-1], len(rest))
                    self.history__.append(record)
                    self.history_tracking__ = False
824
825
826
827
        if stitches:
            if rest:
                stitches.append(Node(None, rest))
            result = Node(None, tuple(stitches))
828
        if any(self.variables__.values()):
Eckhart Arnold's avatar
Eckhart Arnold committed
829
830
831
832
833
834
835
836
837
838
839
            error_str = "Capture-retrieve-stack not empty after end of parsing: " + \
                            str(self.variables__)
            if result.children:
                # add another child node at the end to ensure that the position
                # of the error will be the end of the text. Otherwise, the error
                # message above ("...after end of parsing") would appear illogical.
                error_node = Node(ZOMBIE_PARSER, '')
                error_node.add_error(error_str)
                result.result = result.children + (error_node,)
            else:
                result.add_error(error_str)
840
841
842
        result.pos = 0  # calculate all positions
        return result

843

844
    def push_rollback__(self, location, func):
845
846
        """
        Adds a rollback function that either removes or re-adds
847
848
849
850
        values on the variable stack (`self.variables`) that have been
        added (or removed) by Capture or Pop Parsers, the results of
        which have been dismissed.
        """
851
        self.rollback__.append((location, func))
852
        # print("push:  line %i, col %i" % line_col(self.document__, len(self.document__) - location))
853
854
        self.last_rb__loc__ = location

855

856
    def rollback_to__(self, location):
857
858
        """
        Rolls back the variable stacks (`self.variables`) to its
859
860
        state at an earlier location in the parsed document.
        """
861
        # print("rollback:  line %i, col %i" % line_col(self.document__, len(self.document__) - location))
862
863
        while self.rollback__ and self.rollback__[-1][0] <= location:
            loc, rollback_func = self.rollback__.pop()
864
865
866
867
            # assert not loc > self.last_rb__loc__, \
            #     "Rollback confusion: line %i, col %i < line %i, col %i" % \
            #     (*line_col(self.document__, len(self.document__) - loc),
            #      *line_col(self.document__, len(self.document__) - self.last_rb__loc__))
868
            rollback_func()
869
            # print("rb to:  line %i, col %i" % line_col(self.document__, len(self.document__) - loc))
870
871
872
        self.last_rb__loc__ == self.rollback__[-1][0] if self.rollback__ \
            else (len(self.document__) + 1)

873

874
    def log_parsing_history__(self, log_file_name: str = '') -> None:
875
876
        """
        Writes a log of the parsing history of the most recently parsed
877
878
879
        document. 
        """
        def prepare_line(record):
880
            excerpt = self.document__.__getitem__(record.extent)[:25].replace('\n', '\\n')
881
            excerpt = "'%s'" % excerpt if len(excerpt) < 25 else "'%s...'" % excerpt
882
            return record.stack, record.status, excerpt
883
884

        def write_log(history, log_name):
Eckhart Arnold's avatar
Eckhart Arnold committed
885
            path = os.path.join(log_dir(), log_name + "_parser.log")
Eckhart Arnold's avatar
Eckhart Arnold committed
886
887
888
            if os.path.exists(path):
                os.remove(path)
                print('WARNING: Log-file "%s" already existed and was deleted.' % path)
889
890
891
892
            if history:
                with open(path, "w", encoding="utf-8") as f:
                    f.write("\n".join(history))

893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
        if is_logging():
            assert self.history__, \
                "Parser did not yet run or logging was turned off when running parser!"
            if not log_file_name:
                name = self.__class__.__name__
                log_file_name = name[:-7] if name.lower().endswith('grammar') else name
            full_history, match_history, errors_only = [], [], []
            for record in self.history__:
                line = ";  ".join(prepare_line(record))
                full_history.append(line)
                if record.node and record.node.parser.ptype != WHITESPACE_PTYPE:
                    match_history.append(line)
                    if record.node.error_flag:
                        errors_only.append(line)
            write_log(full_history, log_file_name + '_full')
            write_log(match_history, log_file_name + '_match')
            write_log(errors_only, log_file_name + '_errors')
910
911


Eckhart Arnold's avatar
Eckhart Arnold committed
912
def dsl_error_msg(parser: Parser, error_str: str) -> str:
913
914
    """
    Returns an error message for errors in the parser configuration,
915
916
917
    e.g. errors that result in infinite loops.

    Args:
Eckhart Arnold's avatar
Eckhart Arnold committed
918
        parser (Parser):  The parser where the error was noticed. Note
919
            that this is not necessarily the parser that caused the
920
            error but only where the error became apparent.
921
922
923
924
925
        error_str (str):  A short string describing the error.
    Returns:  
        str: An error message including the call stack if history 
        tacking has been turned in the grammar object.
    """
926
    msg = ["DSL parser specification error:", error_str, 'Caught by parser "%s".' % str(parser)]
927
928
    if parser.grammar.history__:
        msg.extend(["\nCall stack:", parser.grammar.history__[-1].stack])
929
930
931
932
933
    else:
        msg.extend(["\nEnable history tracking in Grammar object to display call stack."])
    return " ".join(msg)


934

935
936
937
938
939
940
941
########################################################################
#
# Token and Regular Expression parser classes (i.e. leaf classes)
#
########################################################################


942
943
944
RX_PREPROCESSOR_TOKEN = re.compile('\w+')
BEGIN_TOKEN = '\x1b'
END_TOKEN = '\x1c'
945
946


947
def make_token(token: str, argument: str = '') -> str:
948
949
    """
    Turns the ``token`` and ``argument`` into a special token that
950
    will be caught by the `PreprocessorToken`-parser.
951

952
953
    This function is a support function that should be used by
    preprocessors to inject preprocessor tokens into the source text.
954
    """
955
956
957
    assert RX_PREPROCESSOR_TOKEN.match(token)
    assert argument.find(BEGIN_TOKEN) < 0
    assert argument.find(END_TOKEN) < 0
958

959
    return BEGIN_TOKEN + token + argument + END_TOKEN
960
961


962
def nil_preprocessor(text: str) -> str:
Eckhart Arnold's avatar
Eckhart Arnold committed
963
    return text
964
965


966
class PreprocessorToken(Parser):
967
    """
968
    Parses tokens that have been inserted by a preprocessor.
969
    
970
    Preprocessors can generate Tokens with the ``make_token``-function.
971
    These tokens start and end with magic characters that can only be
972
973
974
    matched by the PreprocessorToken Parser. Such tokens can be used to
    insert BEGIN - END delimiters at the beginning or ending of a
    quoted block, for example.
975
    """
976

977
978
979
980
    def __init__(self, token: str) -> None:
        assert token and token.isupper()
        assert RX_PREPROCESSOR_TOKEN.match(token)
        super(PreprocessorToken, self).__init__(token)
981

982
    def __call__(self, text: str) -> Tuple[Node, str]:
983
984
        if text[0:1] == BEGIN_TOKEN:
            end = text.find(END_TOKEN, 1)
985
986
            if end < 0:
                node = Node(self, '').add_error(
987
988
                    'END_TOKEN delimiter missing from preprocessor token. '
                    '(Most likely due to a preprocessor bug!)')  # type: Node
989
990
991
                return node, text[1:]
            elif end == 0:
                node = Node(self, '').add_error(
992
993
                    'Preprocessor-token cannot have zero length. '
                    '(Most likely due to a preprocessor bug!)')
994
                return node, text[2:]
995
            elif text.find(BEGIN_TOKEN, 1, end) >= 0:
996
997
                node = Node(self, text[len(self.name) + 1:end])
                node.add_error(
998
999
1000
                    'Preprocessor-tokens must not be nested or contain '
                    'BEGIN_TOKEN delimiter as part of their argument. '
                    '(Most likely due to a preprocessor bug!)')
1001
1002
1003
1004
1005
1006
1007
1008
                return node, text[end:]
            if text[1:len(self.name) + 1] == self.name:
                return Node(self, text[len(self.name) + 1:end]), \
                       text[end + 1:]
        return None, text


class RegExp(Parser):
Eckhart Arnold's avatar
Eckhart Arnold committed
1009
    """Regular expression parser.
1010
1011
1012
1013
1014
    
    The RegExp-parser parses text that matches a regular expression.
    RegExp can also be considered as the "atomic parser", because all
    other parsers delegate part of the parsing job to other parsers,
    but do not match text directly.
Eckhart Arnold's avatar
Eckhart Arnold committed
1015
1016
1017
1018
1019
1020
1021
1022

    Example:
    >>> word = RegExp(r'\w+')
    >>> Grammar(word)("Haus").content()
    'Haus'

    EBNF-Notation:  `/ ... /`
    EBNF-Example:   `word = /\w+/`
1023
    """
1024
1025

    def __init__(self, regexp, name: str = '') -> None:
1026
        super(RegExp, self).__init__(name)
1027
1028
1029
        self.regexp = re.compile(regexp) if isinstance(regexp, str) else regexp

    def __deepcopy__(self, memo):
Eckhart Arnold's avatar
Eckhart Arnold committed
1030
        # `regex` supports deep copies, but not `re`
1031
        try:
Eckhart Arnold's avatar
Eckhart Arnold committed
1032
            regexp = copy.deepcopy(self.regexp, memo)
1033
1034
        except TypeError:
            regexp = self.regexp.pattern
1035
        return RegExp(regexp, self.name)
1036

1037
    def __call__(self, text: str) -> Tuple[Node, str]:
1038
        match = text[0:1] != BEGIN_TOKEN and self.regexp.match(text)  # ESC starts a preprocessor token.
1039
1040
1041
1042
1043
        if match:
            end = match.end()
            return Node(self, text[:end]), text[end:]
        return None, text

1044
    def __repr__(self):
1045
        return '/%s/' % self.regexp.pattern
1046

1047

1048
1049
class Whitespace(RegExp):
    assert WHITESPACE_PTYPE == ":Whitespace"
1050
1051


1052
class RE(Parser):
1053
1054
    """
    Regular Expressions with optional leading or trailing whitespace.
1055
1056
    
    The RE-parser parses pieces of text that match a given regular
Eckhart Arnold's avatar
Eckhart Arnold committed
1057
    expression. Other than the ``RegExp``-Parser it can also skip
1058
1059
    "implicit whitespace" before or after the matched text.
    
Eckhart Arnold's avatar
Eckhart Arnold committed
1060
1061
1062
1063
1064
    The whitespace is in turn defined by a regular expression. It should
    be made sure that this expression also matches the empty string,
    e.g. use r'\s*' or r'[\t ]+', but not r'\s+'. If the respective
    parameters in the constructor are set to ``None`` the default
    whitespace expression from the Grammar object will be used.
Eckhart Arnold's avatar
Eckhart Arnold committed
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079

    Example (allowing whitespace on the right hand side, but not on
    the left hand side of a regular expression):
    >>> word = RE(r'\w+', wR=r'\s*')
    >>> parser = Grammar(word)
    >>> result = parser('Haus ')
    >>> result.content()
    'Haus '
    >>> result.structure()
    '(:RE (:RegExp "Haus") (:Whitespace " "))'
    >>> parser(' Haus').content()
    ' <<< Error on " Haus" | Parser did not match! Invalid source file? >>> '

    EBNF-Notation:  `/ ... /~`  or  `~/ ... /`  or  `~/ ... /~`
    EBNF-Example:   `word = /\w+/~`
1080
    """
1081
    def __init__(self, regexp, wL=None, wR=None, name=''):
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
        """Constructor for class RE.
                
        Args:
            regexp (str or regex object):  The regular expression to be
                used for parsing. 
            wL (str or regexp):  Left whitespace regular expression, 
                i.e. either ``None``, the empty string or a regular
                expression (e.g. "\s*") that defines whitespace. An 
                empty string means no whitespace will be skipped,
                ``None`` means that the default whitespace will be 
                used.
            wR (str or regexp):  Right whitespace regular expression.
                See above.
            name:  The optional name of the parser.
        """
1097
        super(RE, self).__init__(name)
1098
1099
        self.wL = wL
        self.wR = wR
1100
1101
        self.wspLeft = Whitespace(wL) if wL else ZOMBIE_PARSER
        self.wspRight = Whitespace(wR) if wR else ZOMBIE_PARSER
1102
1103
        self.main = RegExp(regexp)

Eckhart Arnold's avatar
Eckhart Arnold committed
1104
1105
1106
1107
1108
    def __deepcopy__(self, memo={}):
        try:
            regexp = copy.deepcopy(self.main.regexp, memo)
        except TypeError:
            regexp = self.main.regexp.pattern
1109
        return self.__class__(regexp, self.wL, self.wR, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
1110