parser.py 81.3 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, \
78
    StringView, EMPTY_STRING_VIEW
79
80
from DHParser.syntaxtree import Node, TransformationFunc, ParserBase, WHITESPACE_PTYPE, TOKEN_PTYPE, \
    ZOMBIE_PARSER
81
from DHParser.error import Error, is_error, has_errors, linebreaks, line_col
82
from DHParser.toolkit import load_if_file
Eckhart Arnold's avatar
Eckhart Arnold committed
83

84
__all__ = ('PreprocessorFunc',
85
           'HistoryRecord',
Eckhart Arnold's avatar
Eckhart Arnold committed
86
           'Parser',
87
           'Grammar',
88
89
90
           'RX_PREPROCESSOR_TOKEN',
           'BEGIN_TOKEN',
           'END_TOKEN',
Eckhart Arnold's avatar
Eckhart Arnold committed
91
           'make_token',
92
93
           'nil_preprocessor',
           'PreprocessorToken',
Eckhart Arnold's avatar
Eckhart Arnold committed
94
95
96
97
           'RegExp',
           'RE',
           'Token',
           'mixin_comment',
98
99
100
           # 'UnaryOperator',
           # 'NaryOperator',
           'Synonym',
101
           'Option',
Eckhart Arnold's avatar
Eckhart Arnold committed
102
103
           'ZeroOrMore',
           'OneOrMore',
104
           'Series',
Eckhart Arnold's avatar
Eckhart Arnold committed
105
106
107
108
109
110
111
           'Alternative',
           'FlowOperator',
           'Required',
           'Lookahead',
           'NegativeLookahead',
           'Lookbehind',
           'NegativeLookbehind',
112
113
114
           'last_value',
           'counterpart',
           'accumulate',
Eckhart Arnold's avatar
Eckhart Arnold committed
115
116
117
118
           'Capture',
           'Retrieve',
           'Pop',
           'Forward',
119
           'Compiler',
120
           'compile_source')
Eckhart Arnold's avatar
Eckhart Arnold committed
121

122

123

124
125
126
127
128
129
130
########################################################################
#
# Grammar and parsing infrastructure
#
########################################################################


131
PreprocessorFunc = Union[Callable[[str], str], partial]
132
133


134
135
136
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
137
MAX_DROPOUTS = 3  # type: int
138
# stop trying to recover parsing after so many errors
139

140

141
142
143
144
145
146
147
148
149
150
151
152
153
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.
    """
154
    __slots__ = ('call_stack', 'node', 'remaining', 'line_col')
155
156
157
158
159

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

160
    def __init__(self, call_stack: List['Parser'], node: Node, remaining: int) -> None:
161
        # copy call stack, dropping uninformative Forward-Parsers
Eckhart Arnold's avatar
Eckhart Arnold committed
162
        self.call_stack = [p for p in call_stack if p.ptype != ":Forward"]  # type: List['Parser']
163
164
        self.node = node                # type: Node
        self.remaining = remaining      # type: int
165
166
        self.line_col = (1, 1)          # type: Tuple[int, int]
        if call_stack:
167
168
169
170
            grammar = call_stack[-1].grammar
            document = grammar.document__
            lbreaks = grammar.document_lbreaks__
            self.line_col = line_col(lbreaks, len(document) - remaining)
171
172
173
174

    def __str__(self):
        return 'line %i, column %i:  %s  "%s"' % \
               (self.line_col[0], self.line_col[1], self.stack, str(self.node))
175

176
    def err_msg(self) -> str:
177
        return self.ERROR + ": " + "; ".join(str(e) for e in self.node._errors).replace('\n', '\\')
178

179
    @property
180
    def stack(self) -> str:
181
        return "->".join((p.repr if p.ptype == ':RegExp' else p.name or p.ptype)
182
                         for p in self.call_stack)
183
184

    @property
185
    def status(self) -> str:
186
        return self.FAIL if self.node is None else \
187
            self.err_msg() if has_errors(self.node._errors) else self.MATCH
188
189

    @property
190
    def extent(self) -> slice:
191
        return (slice(-self.remaining - len(self.node), -self.remaining) if self.node
192
                else slice(-self.remaining, None))
193

194
    @staticmethod
Eckhart Arnold's avatar
Eckhart Arnold committed
195
    def last_match(history: List['HistoryRecord']) -> Union['HistoryRecord', None]:
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
        """
        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
Eckhart Arnold's avatar
Eckhart Arnold committed
211
    def most_advanced_match(history: List['HistoryRecord']) -> Union['HistoryRecord', None]:
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
        """
        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


231
def add_parser_guard(parser_func):
232
233
234
235
236
    """
    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.
    """
237
    def guarded_call(parser: 'Parser', text: StringView) -> Tuple[Node, StringView]:
di68kap's avatar
di68kap committed
238
239
240
241
242
243
244
245
246
247
248
        # 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 EMPTY_STRING_VIEW
        #     return node, rest
        #     # NOTE: An older and simpler implementation of memoization
        #     # relied on `parser.visited[location] == node, rest`. Although,
        #     # rest is really just a substring of one and the same document,
        #     # this resulted in an explosion of memory usage. Seems that
        #     # `rext = text[i:]` really copies the sub-string. See:
        #     # https://mail.python.org/pipermail/python-dev/2008-May/079699.html
249

250
        try:
251
            location = len(text)    # mind that location is always the distance to the end
252
253
            grammar = parser.grammar  # grammar may be 'None' for unconnected parsers!

254
255
            if grammar.last_rb__loc__ <= location:
                grammar.rollback_to__(location)
256

257
258
259
            # if location has already been visited by the current parser,
            # return saved result
            if location in parser.visited:
di68kap's avatar
di68kap committed
260
                return parser.visited[location]
261

Eckhart Arnold's avatar
Eckhart Arnold committed
262
263
            if grammar.history_tracking__:
                grammar.call_stack__.append(parser)
264
                grammar.moving_forward__ = True
Eckhart Arnold's avatar
Eckhart Arnold committed
265

266
267
268
269
270
271
            # break left recursion at the maximum allowed depth
            if grammar.left_recursion_handling__:
                if parser.recursion_counter.setdefault(location, 0) > LEFT_RECURSION_DEPTH:
                    grammar.recursion_locations__.add(location)
                    return None, text
                parser.recursion_counter[location] += 1
272
273
274
275

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

276
277
278
            if grammar.left_recursion_handling__:
                parser.recursion_counter[location] -= 1

279
            if node is None:
280
                # retrieve an earlier match result (from left recursion) if it exists
281
282
                if location in grammar.recursion_locations__:
                    if location in parser.visited:
di68kap's avatar
di68kap committed
283
                        node, rest = parser.visited[location]
284
                        # TODO: maybe add a warning about occurrence of left-recursion here?
285
286
287
                    # 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__:
288
                    # otherwise also cache None-results
di68kap's avatar
di68kap committed
289
                    parser.visited[location] = (None, rest)
Eckhart Arnold's avatar
Eckhart Arnold committed
290
291
            elif (grammar.last_rb__loc__ > location
                  and (grammar.memoization__ or location in grammar.recursion_locations__)):
292
293
294
295
                # - 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
di68kap's avatar
di68kap committed
296
                parser.visited[location] = (node, rest)
297

298
            if grammar.history_tracking__:
299
                # don't track returning parsers except in case an error has occurred
300
                remaining = len(rest)
301
                if grammar.moving_forward__ or (node and node._errors):
302
                    record = HistoryRecord(grammar.call_stack__, node, remaining)
303
                    grammar.history__.append(record)
304
                    # print(record.stack, record.status, rest[:20].replace('\n', '|'))
305
                grammar.moving_forward__ = False
306
                grammar.call_stack__.pop()
307

308
        except RecursionError:
309
            node = Node(None, str(text[:min(10, max(1, text.find("\n")))]) + " ...")
310
311
            node.add_error("maximum recursion depth of parser reached; "
                           "potentially due to too many errors!")
312
            rest = EMPTY_STRING_VIEW
313
314
315
316
317
318

        return node, rest

    return guarded_call


Eckhart Arnold's avatar
Eckhart Arnold committed
319
class ParserMetaClass(abc.ABCMeta):
320
321
322
323
324
    """
    ParserMetaClass adds a wrapper to the __call__ method of parser
    objects during initialization that takes care of memoizing,
    left recursion and tracing.
    """
325
    def __init__(cls, name, bases, attrs):
326
327
        guarded_parser_call = add_parser_guard(cls.__call__)
        # The following check is necessary for classes that don't override
328
329
330
331
332
333
334
        # 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
335
class Parser(ParserBase, metaclass=ParserMetaClass):
336
337
338
339
    """
    (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.
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356

    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
357
358

    Parser objects are callable and parsing is done by calling a parser
Eckhart Arnold's avatar
Eckhart Arnold committed
359
360
361
362
363
364
    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
365
    `ZeroOrMore` or `Option`). If `i > 0` then the parser has "moved
Eckhart Arnold's avatar
Eckhart Arnold committed
366
367
368
369
370
371
    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.
372
373

    Attributes:
374
        visited:  Mapping of places this parser has already been to
di68kap's avatar
di68kap committed
375
                during the current parsing process onto the results the
376
377
378
379
380
381
382
383
                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.

384
        cycle_detection:  The apply()-method uses this variable to make
385
386
387
                sure that one and the same function will not be applied
                (recursively) a second time, if it has already been
                applied to this parser.
388
389
390

        grammar:  A reference to the Grammar object to which the parser
                is attached.
391
392
    """

393
394
    ApplyFunc = Callable[['Parser'], None]

395
396
    def __init__(self, name: str = '') -> None:
        # assert isinstance(name, str), str(name)
Eckhart Arnold's avatar
Eckhart Arnold committed
397
        super(Parser, self).__init__(name)
398
        self._grammar = None  # type: 'Grammar'
399
400
        self.reset()

Eckhart Arnold's avatar
Eckhart Arnold committed
401
    def __deepcopy__(self, memo):
Eckhart Arnold's avatar
Eckhart Arnold committed
402
403
404
405
406
407
        """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.
        """
408
409
        return self.__class__(self.name)

410
    def reset(self):
Eckhart Arnold's avatar
Eckhart Arnold committed
411
412
413
        """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."""
di68kap's avatar
di68kap committed
414
        self.visited = dict()            # type: Dict[int, Tuple[Node, StringView]]
415
        self.recursion_counter = dict()  # type: Dict[int, int]
416
        self.cycle_detection = set()     # type: Set[Callable]
417
        return self
418

419
    def __call__(self, text: StringView) -> Tuple[Node, StringView]:
Eckhart Arnold's avatar
Eckhart Arnold committed
420
421
422
        """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."""
423
424
        return None, text  # default behaviour: don't match

425
    def __add__(self, other: 'Parser') -> 'Series':
426
427
        """The + operator generates a series-parser that applies two
        parsers in sequence."""
428
        return Series(self, other)
429

430
    def __or__(self, other: 'Parser') -> 'Alternative':
431
432
433
        """The | operator generates an alternative parser that applies
        the first parser and, if that does not match, the second parser.
        """
434
435
        return Alternative(self, other)

436
    @property
437
    def grammar(self) -> 'Grammar':
438
439
440
        return self._grammar

    @grammar.setter
441
    def grammar(self, grammar: 'Grammar'):
Eckhart Arnold's avatar
Eckhart Arnold committed
442
443
444
445
446
447
        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!"
448
449

    def _grammar_assigned_notifier(self):
450
451
        """A function that notifies the parser object that it has been
        assigned to a grammar."""
452
453
        pass

454
    def apply(self, func: ApplyFunc):
455
456
        """
        Applies function `func(parser)` recursively to this parser and all
Eckhart Arnold's avatar
Eckhart Arnold committed
457
        descendant parsers if any exist. The same function can never
458
459
460
461
462
463
464
465
466
467
        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


468
def mixin_comment(whitespace: str, comment: str) -> str:
469
470
    """
    Returns a regular expression that merges comment and whitespace
471
472
473
474
475
476
477
478
479
480
481
    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


482
class Grammar:
483
    """
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
    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
499
        >>> number_parser("3.1416").content()
500
501
        '3.1416'

Eckhart Arnold's avatar
Eckhart Arnold committed
502
    Collecting the parsers that define a grammar in a descendant class of
503
504
505
506
507
508
509
    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
Eckhart Arnold's avatar
Eckhart Arnold committed
510
511
       assign them to class variables, which results in better
       readability of the Python code.
512

Eckhart Arnold's avatar
Eckhart Arnold committed
513
514
515
    3. The parsers in the 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.
516
517
518
519
520
521

    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.
522
523

    Example:
524

525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
        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,
543
544
545
    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.
546
547
548
549
550
551
552
553
554
555
556
    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.

557
    Grammar classes contain a few special class fields for implicit
558
559
    whitespace and comments that should be overwritten, if the defaults
    (no comments, horizontal right aligned whitespace) don't fit:
560
561
    COMMENT__:  regular expression string for matching comments
    WSP__:   regular expression for whitespace and comments
Eckhart Arnold's avatar
Eckhart Arnold committed
562

563
564
    wspL__:  regular expression string for left aligned whitespace,
             which either equals WSP__ or is empty.
Eckhart Arnold's avatar
Eckhart Arnold committed
565

566
567
    wspR__:  regular expression string for right aligned whitespace,
             which either equals WSP__ or is empty.
Eckhart Arnold's avatar
Eckhart Arnold committed
568

569
570
571
572
    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.
Eckhart Arnold's avatar
Eckhart Arnold committed
573

574
575
576
577
578
579
580
581
582
    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

Eckhart Arnold's avatar
Eckhart Arnold committed
583
        history_tracking__:  A flag indicating that the parsing history shall
584
585
586
587
588
589
590
                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'.
Eckhart Arnold's avatar
Eckhart Arnold committed
591

592
593
594
595
596
597
598
599
600
601
602
        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.
Eckhart Arnold's avatar
Eckhart Arnold committed
603

604
605
606
607
608
        document_lbreaks__:  list of linebreaks within the document, starting
                with -1 and ending with EOF. This helps generating line
                and column number for history recording and will only be
                initialized if `history_tracking__` is true.

609
610
        _reversed__:  the same text in reverse order - needed by the `Lookbehind'-
                parsers.
Eckhart Arnold's avatar
Eckhart Arnold committed
611

612
613
614
        variables__:  A mapping for variable names to a stack of their respective
                string values - needed by the `Capture`-, `Retrieve`- and `Pop`-
                parsers.
Eckhart Arnold's avatar
Eckhart Arnold committed
615

616
617
618
619
620
        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.
Eckhart Arnold's avatar
Eckhart Arnold committed
621

622
623
624
625
626
627
628
629
        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)`.
Eckhart Arnold's avatar
Eckhart Arnold committed
630

631
632
633
634
        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.
Eckhart Arnold's avatar
Eckhart Arnold committed
635

636
637
638
        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.
Eckhart Arnold's avatar
Eckhart Arnold committed
639

640
641
642
643
644
        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`)
Eckhart Arnold's avatar
Eckhart Arnold committed
645

646
647
648
649
650
        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`)
Eckhart Arnold's avatar
Eckhart Arnold committed
651

652
653
654
        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
655
656
657
658
659
                it is safer to leave it on. (Default: on)

        left_recursion_handling__:  Turns left recursion handling on or off.
                If turned off, a recursion error will result in case of left
                recursion.
660
    """
661
662
    root__ = None  # type: Union[Parser, None]
    # root__ must be overwritten with the root-parser by grammar subclass
Eckhart Arnold's avatar
Eckhart Arnold committed
663
    parser_initialization__ = "pending"  # type: str
664
    # some default values
Eckhart Arnold's avatar
Eckhart Arnold committed
665
666
667
668
    COMMENT__ = r''  # type: str  # r'#.*(?:\n|$)'
    WSP__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)  # type: str
    wspL__ = ''     # type: str
    wspR__ = WSP__  # type: str
669

670

671
    @classmethod
672
    def _assign_parser_names__(cls):
673
674
        """
        Initializes the `parser.name` fields of those
675
676
        Parser objects that are directly assigned to a class field with
        the field's name, e.g.
677
            class Grammar(Grammar):
678
679
680
                ...
                symbol = RE('(?!\\d)\\w+')
        After the call of this method symbol.name == "symbol"
681
682
683
684
        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()``
685
686
687
688

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

689
690
691
692
693
        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. 
694
        """
695
696
697
698
699
        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:
700
701
702
                        parser._name = entry
                    if (isinstance(parser, Forward) and (not parser.parser._name)):
                        parser.parser._name = entry
703
            cls.parser_initialization__ = "done"
704

705

Eckhart Arnold's avatar
Eckhart Arnold committed
706
707
708
    def __init__(self, root: Parser=None) -> None:
        # if not hasattr(self.__class__, 'parser_initialization__'):
        #     self.__class__.parser_initialization__ = "pending"
709
710
711
712
        # if not hasattr(self.__class__, 'wspL__'):
        #     self.wspL__ = ''
        # if not hasattr(self.__class__, 'wspR__'):
        #     self.wspR__ = ''
713
714
715
716
        self.all_parsers__ = set()             # type: Set[Parser]
        self._dirty_flag__ = False             # type: bool
        self.history_tracking__ = False        # type: bool
        self.memoization__ = True              # type: bool
717
        self.left_recursion_handling__ = True  # type: bool
718
        self._reset__()
719

Eckhart Arnold's avatar
Eckhart Arnold committed
720
        # prepare parsers in the class, first
721
        self._assign_parser_names__()
722

Eckhart Arnold's avatar
Eckhart Arnold committed
723
724
725
726
        # 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
727
        self.root__ = copy.deepcopy(root) if root else copy.deepcopy(self.__class__.root__)
728

729
        if self.wspL__:
Eckhart Arnold's avatar
Eckhart Arnold committed
730
            self.wsp_left_parser__ = Whitespace(self.wspL__)  # type: ParserBase
731
            self.wsp_left_parser__.grammar = self
732
            self.all_parsers__.add(self.wsp_left_parser__)  # don't you forget about me...
733
734
735
        else:
            self.wsp_left_parser__ = ZOMBIE_PARSER
        if self.wspR__:
Eckhart Arnold's avatar
Eckhart Arnold committed
736
            self.wsp_right_parser__ = Whitespace(self.wspR__)  # type: ParserBase
737
            self.wsp_right_parser__.grammar = self
738
            self.all_parsers__.add(self.wsp_right_parser__)  # don't you forget about me...
739
740
        else:
            self.wsp_right_parser__ = ZOMBIE_PARSER
741
        self.root__.apply(self._add_parser__)
742

743

744
    def __getitem__(self, key):
745
746
747
        try:
            return self.__dict__[key]
        except KeyError:
748
749
            parser_template = getattr(self, key, None)
            if parser_template:
Eckhart Arnold's avatar
Eckhart Arnold committed
750
                # add parser to grammar object on the fly...
751
                parser = copy.deepcopy(parser_template)
752
                parser.apply(self._add_parser__)
753
                # assert self[key] == parser
Eckhart Arnold's avatar
Eckhart Arnold committed
754
                return self[key]
755
            raise KeyError('Unknown parser "%s" !' % key)
756

757

758
    def _reset__(self):
759
760
        self.document__ = EMPTY_STRING_VIEW   # type: StringView
        self._reversed__ = EMPTY_STRING_VIEW  # type: StringView
761
        self.document_lbreaks__ = []          # type: List[int]
762
        # variables stored and recalled by Capture and Retrieve parsers
763
764
        self.variables__ = dict()     # type: Dict[str, List[str]]
        self.rollback__ = []          # type: List[Tuple[int, Callable]]
765
        self.last_rb__loc__ = -1  # type: int
766
        # support for call stack tracing
767
        self.call_stack__ = []        # type: List[Parser]
768
        # snapshots of call stacks
769
        self.history__ = []           # type: List[HistoryRecord]
770
        # also needed for call stack tracing
771
772
        self.moving_forward__ = False  # type: bool
        self.recursion_locations__ = set()  # type: Set[int]
773

774

Eckhart Arnold's avatar
Eckhart Arnold committed
775
    @property
Eckhart Arnold's avatar
Eckhart Arnold committed
776
    def reversed__(self) -> StringView:
Eckhart Arnold's avatar
Eckhart Arnold committed
777
        if not self._reversed__:
778
            self._reversed__ = StringView(self.document__.text[::-1])
Eckhart Arnold's avatar
Eckhart Arnold committed
779
780
781
        return self._reversed__


782
    def _add_parser__(self, parser: Parser) -> None:
783
784
        """
        Adds the particular copy of the parser object to this
785
        particular instance of Grammar.
786
        """
787
        if parser.name:
Eckhart Arnold's avatar
Eckhart Arnold committed
788
789
790
            # 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__), \
791
792
                ('Cannot add parser "%s" because a field with the same name '
                 'already exists in grammar object!' % parser.name)
793
            setattr(self, parser.name, parser)
794
        self.all_parsers__.add(parser)
795
796
        parser.grammar = self

797

Eckhart Arnold's avatar
Eckhart Arnold committed
798
    def __call__(self, document: str, start_parser="root__") -> Node:
799
800
        """
        Parses a document with with parser-combinators.
801
802
803

        Args:
            document (str): The source text to be parsed.
804
805
806
            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.)
807
808
809
        Returns:
            Node: The root node ot the parse tree.
        """
810
        # assert isinstance(document, str), type(document)
811
812
        if self.root__ is None:
            raise NotImplementedError()
813
        if self._dirty_flag__:
814
            self._reset__()
815
            for parser in self.all_parsers__:
816
817
                parser.reset()
        else:
818
            self._dirty_flag__ = True
819
        self.history_tracking__ = is_logging()
820
        self.document__ = StringView(document)
821
        self.document_lbreaks__ = linebreaks(document) if self.history_tracking__ else []
822
        self.last_rb__loc__ = len(self.document__) + 1  # rollback location
Eckhart Arnold's avatar
Eckhart Arnold committed
823
        parser = self[start_parser] if isinstance(start_parser, str) else start_parser
824
825
        assert parser.grammar == self, "Cannot run parsers from a different grammar object!" \
                                       " %s vs. %s" % (str(self), str(parser.grammar))
826
        stitches = []  # type: List[Node]
827
        rest = self.document__
828
829
        if not rest:
            result, ignore = parser(rest)
di68kap's avatar
di68kap committed
830
831
832
            if result is None:
                result = Node(None, '')
                result.add_error('Parser "%s" did not match empty document.' % str(parser))
833
834
835
836
837
838
        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:
839
840
841
842
                    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__)))
843
844
845
                else:
                    stitches.append(result)
                    error_msg = "Parser stopped before end" + \
846
847
                                (("! trying to recover" +
                                  (" but stopping history recording at this point."
848
                                   if self.history_tracking__ else "..."))
849
850
851
852
                                 if len(stitches) < MAX_DROPOUTS
                                 else " too often! Terminating parser.")
                stitches.append(Node(None, skip))
                stitches[-1].add_error(error_msg)
853
                if self.history_tracking__:
854
                    # some parsers may have matched and left history records with nodes != None.
855
                    # Because these are not connected to the stitched root node, their pos-
856
857
                    # properties will not be initialized by setting the root node's pos property
                    # to zero. Therefore, their pos properties need to be initialized here
858
                    for record in self.history__:
859
860
                        if record.node and record.node._pos < 0:
                            record.node.pos = 0
861
862
863
                    record = HistoryRecord(self.call_stack__.copy(), stitches[-1], len(rest))
                    self.history__.append(record)
                    self.history_tracking__ = False
864
865
866
867
        if stitches:
            if rest:
                stitches.append(Node(None, rest))
            result = Node(None, tuple(stitches))
868
        if any(self.variables__.values()):
Eckhart Arnold's avatar
Eckhart Arnold committed
869
870
871
872
873
874
875
876
877
878
879
            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)
880
        result.pos = 0  # calculate all positions
881
        # result.collect_errors(self.document__)
882
883
        return result

884

885
    def push_rollback__(self, location, func):
886
887
        """
        Adds a rollback function that either removes or re-adds
888
889
890
891
        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.
        """
892
        self.rollback__.append((location, func))
893
        # print("push:  line %i, col %i" % line_col(self.document__, len(self.document__) - location))
894
895
        self.last_rb__loc__ = location

896

897
    def rollback_to__(self, location):
898
899
        """
        Rolls back the variable stacks (`self.variables`) to its
900
901
        state at an earlier location in the parsed document.
        """
902
        # print("rollback:  line %i, col %i" % line_col(self.document__, len(self.document__) - location))
903
904
        while self.rollback__ and self.rollback__[-1][0] <= location:
            loc, rollback_func = self.rollback__.pop()
905
906
907
908
            # 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__))
909
            rollback_func()
910
            # print("rb to:  line %i, col %i" % line_col(self.document__, len(self.document__) - loc))
911
912
913
        self.last_rb__loc__ == self.rollback__[-1][0] if self.rollback__ \
            else (len(self.document__) + 1)

914

915
    def log_parsing_history__(self, log_file_name: str = '') -> None:
916
917
        """
        Writes a log of the parsing history of the most recently parsed
918
919
920
        document. 
        """
        def prepare_line(record):
921
            excerpt = self.document__.text.__getitem__(record.extent)[:25].replace('\n', '\\n')
922
            excerpt = "'%s'" % excerpt if len(excerpt) < 25 else "'%s...'" % excerpt
923
            return record.stack, record.status, excerpt
924
925

        def write_log(history, log_name):
Eckhart Arnold's avatar
Eckhart Arnold committed
926
            path = os.path.join(log_dir(), log_name + "_parser.log")
Eckhart Arnold's avatar
Eckhart Arnold committed
927
928
929
            if os.path.exists(path):
                os.remove(path)
                print('WARNING: Log-file "%s" already existed and was deleted.' % path)
930
931
932
933
            if history:
                with open(path, "w", encoding="utf-8") as f:
                    f.write("\n".join(history))

934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
        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')
951
952


Eckhart Arnold's avatar
Eckhart Arnold committed
953
def dsl_error_msg(parser: Parser, error_str: str) -> str:
954
955
    """
    Returns an error message for errors in the parser configuration,
956
957
958
    e.g. errors that result in infinite loops.

    Args:
Eckhart Arnold's avatar
Eckhart Arnold committed
959
        parser (Parser):  The parser where the error was noticed. Note
960
            that this is not necessarily the parser that caused the
961
            error but only where the error became apparent.
962
963
964
965
966
        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.
    """
967
    msg = ["DSL parser specification error:", error_str, 'Caught by parser "%s".' % str(parser)]
968
969
    if parser.grammar.history__:
        msg.extend(["\nCall stack:", parser.grammar.history__[-1].stack])
970
971
972
973
974
    else:
        msg.extend(["\nEnable history tracking in Grammar object to display call stack."])
    return " ".join(msg)


975

976
977
978
979
980
981
982
########################################################################
#
# Token and Regular Expression parser classes (i.e. leaf classes)
#
########################################################################


983
984
985
RX_PREPROCESSOR_TOKEN = re.compile('\w+')
BEGIN_TOKEN = '\x1b'
END_TOKEN = '\x1c'
986
987


988
def make_token(token: str, argument: str = '') -> str:
989
990
    """
    Turns the ``token`` and ``argument`` into a special token that
991
    will be caught by the `PreprocessorToken`-parser.
992

993
994
    This function is a support function that should be used by
    preprocessors to inject preprocessor tokens into the source text.
995
    """
996
997
998
    assert RX_PREPROCESSOR_TOKEN.match(token)
    assert argument.find(BEGIN_TOKEN) < 0
    assert argument.find(END_TOKEN) < 0
999

1000
    return BEGIN_TOKEN + token + argument + END_TOKEN
For faster browsing, not all history is shown. View entire blame