parser.py 74.3 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
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
177
        return "->".join((repr(p) if p.ptype == ':RegExp' else p.name or p.ptype)
                         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
        try:
234
            location = len(text)    # mind that location is always the distance to the end
235
236
            grammar = parser.grammar  # grammar may be 'None' for unconnected parsers!

237
            if not grammar.moving_forward__:
238
                # rollback variable changes from discarded parser passes
239
240
241
                if grammar.last_rb__loc__ <= location:
                    grammar.rollback_to__(location)
                grammar.moving_forward__ = True
242
                grammar.left_recursion_encountered__ = False
243

244
245
246
            # if location has already been visited by the current parser,
            # return saved result
            if location in parser.visited:
247
                return parser.visited[location]
248

249
250
            # break left recursion at the maximum allowed depth
            if parser.recursion_counter.setdefault(location, 0) > LEFT_RECURSION_DEPTH:
251
                grammar.left_recursion_encountered__ = True
252
253
                return None, text

Eckhart Arnold's avatar
Eckhart Arnold committed
254
255
256
            if grammar.history_tracking__:
                grammar.call_stack__.append(parser)

257
258
259
260
261
            parser.recursion_counter[location] += 1

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

262
            if node is None:
263
                # retrieve an earlier match result (from left recursion) if it exists
Eckhart Arnold's avatar
Eckhart Arnold committed
264
265
266
267
                node, rest = parser.visited.get(location, (None, rest))
                # 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!
                if node is None and not grammar.left_recursion_encountered__:
268
                    # otherwise also cache None-results
269
270
                    parser.visited[location] = None, rest
            else:
271
                # variable manipulating parsers will be excluded, though,
272
                # because caching would interfere with changes of variable state
273
                if grammar.last_rb__loc__ > location:
Eckhart Arnold's avatar
Eckhart Arnold committed
274
275
                    # in case of left recursion, the first recursive step that
                    # matches will store its result in the cache
276
                    parser.visited[location] = (node, rest)
277
278
279

            parser.recursion_counter[location] -= 1

280
            if grammar.history_tracking__:
281
                # don't track returning parsers except in case an error has occurred
282
                if grammar.moving_forward__ or (node and node._errors):
283
                    record = HistoryRecord(grammar.call_stack__, node, len(rest))
284
                    grammar.history__.append(record)
285
                    # print(record.stack, record.status, rest[:20].replace('\n', '|'))
286
287
                grammar.call_stack__.pop()
            grammar.moving_forward__ = False
288

289
290
291
292
293
294
295
296
297
298
299
        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
300
class ParserMetaClass(abc.ABCMeta):
301
302
303
304
305
    """
    ParserMetaClass adds a wrapper to the __call__ method of parser
    objects during initialization that takes care of memoizing,
    left recursion and tracing.
    """
306
    def __init__(cls, name, bases, attrs):
307
308
        guarded_parser_call = add_parser_guard(cls.__call__)
        # The following check is necessary for classes that don't override
309
310
311
312
313
314
315
        # 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
316
class Parser(ParserBase, metaclass=ParserMetaClass):
317
318
319
320
    """
    (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.
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337

    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
338
339

    Parser objects are callable and parsing is done by calling a parser
Eckhart Arnold's avatar
Eckhart Arnold committed
340
341
342
343
344
345
346
347
348
349
350
351
352
    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.
353
354

    Attributes:
355
        visited:  Dictionary of places this parser has already been to
356
357
358
359
360
361
362
363
364
                during the current parsing process and the results the
                parser returned at the respective place. This dictionary
                is used to implement memoizing.

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

365
        cycle_detection:  The apply()-method uses this variable to make
366
367
368
                sure that one and the same function will not be applied
                (recursively) a second time, if it has already been
                applied to this parser.
369
370
371

        grammar:  A reference to the Grammar object to which the parser
                is attached.
372
373
    """

374
375
    ApplyFunc = Callable[['Parser'], None]

376
377
    def __init__(self, name: str = '') -> None:
        # assert isinstance(name, str), str(name)
Eckhart Arnold's avatar
Eckhart Arnold committed
378
        super(Parser, self).__init__(name)
379
        self._grammar = None  # type: 'Grammar'
380
381
        self.reset()

Eckhart Arnold's avatar
Eckhart Arnold committed
382
    def __deepcopy__(self, memo):
Eckhart Arnold's avatar
Eckhart Arnold committed
383
384
385
386
387
388
        """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.
        """
389
390
        return self.__class__(self.name)

391
    def reset(self):
Eckhart Arnold's avatar
Eckhart Arnold committed
392
393
394
        """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."""
395
        self.visited = dict()            # type: Dict[int, Tuple[Node, str]]
396
        self.recursion_counter = dict()  # type: Dict[int, int]
397
        self.cycle_detection = set()     # type: Set[Callable]
398
        return self
399

400
    def __call__(self, text: str) -> Tuple[Node, str]:
Eckhart Arnold's avatar
Eckhart Arnold committed
401
402
403
        """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."""
404
405
        return None, text  # default behaviour: don't match

406
    def __add__(self, other: 'Parser') -> 'Series':
407
408
        """The + operator generates a series-parser that applies two
        parsers in sequence."""
409
        return Series(self, other)
410

411
    def __or__(self, other: 'Parser') -> 'Alternative':
412
413
414
        """The | operator generates an alternative parser that applies
        the first parser and, if that does not match, the second parser.
        """
415
416
        return Alternative(self, other)

417
    @property
418
    def grammar(self) -> 'Grammar':
419
420
421
        return self._grammar

    @grammar.setter
422
    def grammar(self, grammar: 'Grammar'):
Eckhart Arnold's avatar
Eckhart Arnold committed
423
424
425
426
427
428
        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!"
429
430

    def _grammar_assigned_notifier(self):
431
432
        """A function that notifies the parser object that it has been
        assigned to a grammar."""
433
434
        pass

435
    def apply(self, func: ApplyFunc):
436
437
        """
        Applies function `func(parser)` recursively to this parser and all
Eckhart Arnold's avatar
Eckhart Arnold committed
438
        descendant parsers if any exist. The same function can never
439
440
441
442
443
444
445
446
447
448
        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


449
def mixin_comment(whitespace: str, comment: str) -> str:
450
451
    """
    Returns a regular expression that merges comment and whitespace
452
453
454
455
456
457
458
459
460
461
462
    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


463
class Grammar:
464
    """
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
    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
480
        >>> number_parser("3.1416").content()
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
        '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.
502
503

    Example:
504

505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
        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,
523
524
525
    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.
526
527
528
529
530
531
532
533
534
535
536
    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.

537
    Grammar classes contain a few special class fields for implicit
538
539
    whitespace and comments that should be overwritten, if the defaults
    (no comments, horizontal right aligned whitespace) don't fit:
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
    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

559
        hostory_tracking__:  A flag indicating that the parsing history shall
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
                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.
588
589
590
591
592
593
594
595
        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)`.
596
597
598
599
600
601
602
603
604
605
606
607
608
609
        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.
        moving_forward__:  This flag indicates that the parsing process is currently
                moving forward. This information is needed among other thins to
                trigger the roolback of variables, which happens stepwise when the
                parser is reatreating form a dead end, i.e. not moving forward.
                (See `add_parser_guard` and its local function `guarded_call`)
        left_recursion_encountered__:  This flag indicates that left recursion has
                been encountered and triggers the left-recursion algorithm.
610
    """
611
612
    root__ = None  # type: Union[Parser, None]
    # root__ must be overwritten with the root-parser by grammar subclass
Eckhart Arnold's avatar
Eckhart Arnold committed
613
    parser_initialization__ = "pending"  # type: str
614
615
616
617
618
    # some default values
    COMMENT__ = r''  # r'#.*(?:\n|$)'
    WSP__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)
    wspL__ = ''
    wspR__ = WSP__
619

620

621
    @classmethod
622
    def _assign_parser_names__(cls):
623
624
        """
        Initializes the `parser.name` fields of those
625
626
        Parser objects that are directly assigned to a class field with
        the field's name, e.g.
627
            class Grammar(Grammar):
628
629
630
                ...
                symbol = RE('(?!\\d)\\w+')
        After the call of this method symbol.name == "symbol"
631
632
633
634
        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()``
635
636
637
638

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

639
640
641
642
643
        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. 
644
        """
645
646
647
648
649
650
651
652
653
        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"
654

655

Eckhart Arnold's avatar
Eckhart Arnold committed
656
657
658
    def __init__(self, root: Parser=None) -> None:
        # if not hasattr(self.__class__, 'parser_initialization__'):
        #     self.__class__.parser_initialization__ = "pending"
659
660
661
662
        # if not hasattr(self.__class__, 'wspL__'):
        #     self.wspL__ = ''
        # if not hasattr(self.__class__, 'wspR__'):
        #     self.wspR__ = ''
663
        self.all_parsers__ = set()  # type: Set[Parser]
664
665
        self._dirty_flag__ = False  # type: bool
        self.history_tracking__ = False  # type: bool
666
        self._reset__()
667

Eckhart Arnold's avatar
Eckhart Arnold committed
668
        # prepare parsers in the class, first
669
        self._assign_parser_names__()
670

Eckhart Arnold's avatar
Eckhart Arnold committed
671
672
673
674
        # 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
675
        self.root__ = copy.deepcopy(root) if root else copy.deepcopy(self.__class__.root__)
676

677
        if self.wspL__:
Eckhart Arnold's avatar
Eckhart Arnold committed
678
            self.wsp_left_parser__ = Whitespace(self.wspL__)  # type: ParserBase
679
            self.wsp_left_parser__.grammar = self
680
            self.all_parsers__.add(self.wsp_left_parser__)  # don't you forget about me...
681
682
683
        else:
            self.wsp_left_parser__ = ZOMBIE_PARSER
        if self.wspR__:
Eckhart Arnold's avatar
Eckhart Arnold committed
684
            self.wsp_right_parser__ = Whitespace(self.wspR__)  # type: ParserBase
685
            self.wsp_right_parser__.grammar = self
686
            self.all_parsers__.add(self.wsp_right_parser__)  # don't you forget about me...
687
688
        else:
            self.wsp_right_parser__ = ZOMBIE_PARSER
689
        self.root__.apply(self._add_parser__)
690

691

692
    def __getitem__(self, key):
693
694
695
        try:
            return self.__dict__[key]
        except KeyError:
696
697
            parser_template = getattr(self, key, None)
            if parser_template:
Eckhart Arnold's avatar
Eckhart Arnold committed
698
                # add parser to grammar object on the fly...
699
                parser = copy.deepcopy(parser_template)
700
                parser.apply(self._add_parser__)
701
                # assert self[key] == parser
Eckhart Arnold's avatar
Eckhart Arnold committed
702
                return self[key]
703
            raise KeyError('Unknown parser "%s" !' % key)
704

705

706
    def _reset__(self):
707
        self.document__ = ""          # type: str
Eckhart Arnold's avatar
Eckhart Arnold committed
708
        self._reversed__ = ""         # type: str
709
        # variables stored and recalled by Capture and Retrieve parsers
710
711
        self.variables__ = dict()     # type: Dict[str, List[str]]
        self.rollback__ = []          # type: List[Tuple[int, Callable]]
712
        self.last_rb__loc__ = -1  # type: int
713
        # support for call stack tracing
714
        self.call_stack__ = []        # type: List[Parser]
715
        # snapshots of call stacks
716
        self.history__ = []           # type: List[HistoryRecord]
717
        # also needed for call stack tracing
718
        self.moving_forward__ = True  # type: bool
719
        self.left_recursion_encountered__ = False  # type: bool
720

721

Eckhart Arnold's avatar
Eckhart Arnold committed
722
723
724
725
726
727
728
    @property
    def reversed__(self) -> str:
        if not self._reversed__:
            self._reversed__ = self.document__[::-1]
        return self._reversed__


729
    def _add_parser__(self, parser: Parser) -> None:
730
731
        """
        Adds the particular copy of the parser object to this
732
        particular instance of Grammar.
733
        """
734
        if parser.name:
Eckhart Arnold's avatar
Eckhart Arnold committed
735
736
737
            # 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__), \
738
739
                ('Cannot add parser "%s" because a field with the same name '
                 'already exists in grammar object!' % parser.name)
740
            setattr(self, parser.name, parser)
741
        self.all_parsers__.add(parser)
742
743
        parser.grammar = self

744

Eckhart Arnold's avatar
Eckhart Arnold committed
745
    def __call__(self, document: str, start_parser="root__") -> Node:
746
747
        """
        Parses a document with with parser-combinators.
748
749
750

        Args:
            document (str): The source text to be parsed.
751
752
753
            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.)
754
755
756
        Returns:
            Node: The root node ot the parse tree.
        """
757
        # assert isinstance(document, str), type(document)
758
759
        if self.root__ is None:
            raise NotImplementedError()
760
        if self._dirty_flag__:
761
            self._reset__()
762
            for parser in self.all_parsers__:
763
764
                parser.reset()
        else:
765
            self._dirty_flag__ = True
766
767
        self.history_tracking__ = is_logging()
        self.document__ = document
768
        self.last_rb__loc__ = len(document) + 1  # rollback location
Eckhart Arnold's avatar
Eckhart Arnold committed
769
        parser = self[start_parser] if isinstance(start_parser, str) else start_parser
770
771
        assert parser.grammar == self, "Cannot run parsers from a different grammar object!" \
                                       " %s vs. %s" % (str(self), str(parser.grammar))
772
        stitches = []  # type: List[Node]
773
        rest = document
774
775
        if not rest:
            result, ignore = parser(rest)
di68kap's avatar
di68kap committed
776
777
778
            if result is None:
                result = Node(None, '')
                result.add_error('Parser "%s" did not match empty document.' % str(parser))
779
780
781
782
783
784
        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:
785
786
787
788
                    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__)))
789
790
791
                else:
                    stitches.append(result)
                    error_msg = "Parser stopped before end" + \
792
793
                                (("! trying to recover" +
                                  (" but stopping history recording at this point."
794
                                   if self.history_tracking__ else "..."))
795
796
797
798
                                 if len(stitches) < MAX_DROPOUTS
                                 else " too often! Terminating parser.")
                stitches.append(Node(None, skip))
                stitches[-1].add_error(error_msg)
799
                if self.history_tracking__:
800
801
802
803
                    # 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
804
                    for record in self.history__:
805
806
                        if record.node and record.node._pos < 0:
                            record.node.pos = 0
807
808
809
                    record = HistoryRecord(self.call_stack__.copy(), stitches[-1], len(rest))
                    self.history__.append(record)
                    self.history_tracking__ = False
810
811
812
813
        if stitches:
            if rest:
                stitches.append(Node(None, rest))
            result = Node(None, tuple(stitches))
814
        if any(self.variables__.values()):
Eckhart Arnold's avatar
Eckhart Arnold committed
815
816
817
818
819
820
821
822
823
824
825
            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)
826
827
828
        result.pos = 0  # calculate all positions
        return result

829

830
    def push_rollback__(self, location, func):
831
832
        """
        Adds a rollback function that either removes or re-adds
833
834
835
836
        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.
        """
837
        self.rollback__.append((location, func))
838
        # print("push:  line %i, col %i" % line_col(self.document__, len(self.document__) - location))
839
840
        self.last_rb__loc__ = location

841

842
    def rollback_to__(self, location):
843
844
        """
        Rolls back the variable stacks (`self.variables`) to its
845
846
        state at an earlier location in the parsed document.
        """
847
        # print("rollback:  line %i, col %i" % line_col(self.document__, len(self.document__) - location))
848
849
        while self.rollback__ and self.rollback__[-1][0] <= location:
            loc, rollback_func = self.rollback__.pop()
850
851
852
853
            # 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__))
854
            rollback_func()
855
            # print("rb to:  line %i, col %i" % line_col(self.document__, len(self.document__) - loc))
856
857
858
        self.last_rb__loc__ == self.rollback__[-1][0] if self.rollback__ \
            else (len(self.document__) + 1)

859

860
    def log_parsing_history__(self, log_file_name: str = '') -> None:
861
862
        """
        Writes a log of the parsing history of the most recently parsed
863
864
865
        document. 
        """
        def prepare_line(record):
866
            excerpt = self.document__.__getitem__(record.extent)[:25].replace('\n', '\\n')
867
            excerpt = "'%s'" % excerpt if len(excerpt) < 25 else "'%s...'" % excerpt
868
            return record.stack, record.status, excerpt
869
870

        def write_log(history, log_name):
Eckhart Arnold's avatar
Eckhart Arnold committed
871
            path = os.path.join(log_dir(), log_name + "_parser.log")
Eckhart Arnold's avatar
Eckhart Arnold committed
872
873
874
            if os.path.exists(path):
                os.remove(path)
                print('WARNING: Log-file "%s" already existed and was deleted.' % path)
875
876
877
878
            if history:
                with open(path, "w", encoding="utf-8") as f:
                    f.write("\n".join(history))

879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
        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')
896
897


Eckhart Arnold's avatar
Eckhart Arnold committed
898
def dsl_error_msg(parser: Parser, error_str: str) -> str:
899
900
    """
    Returns an error message for errors in the parser configuration,
901
902
903
    e.g. errors that result in infinite loops.

    Args:
Eckhart Arnold's avatar
Eckhart Arnold committed
904
        parser (Parser):  The parser where the error was noticed. Note
905
            that this is not necessarily the parser that caused the
906
            error but only where the error became apparent.
907
908
909
910
911
        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.
    """
912
    msg = ["DSL parser specification error:", error_str, 'Caught by parser "%s".' % str(parser)]
913
914
    if parser.grammar.history__:
        msg.extend(["\nCall stack:", parser.grammar.history__[-1].stack])
915
916
917
918
919
    else:
        msg.extend(["\nEnable history tracking in Grammar object to display call stack."])
    return " ".join(msg)


920

921
922
923
924
925
926
927
########################################################################
#
# Token and Regular Expression parser classes (i.e. leaf classes)
#
########################################################################


928
929
930
RX_PREPROCESSOR_TOKEN = re.compile('\w+')
BEGIN_TOKEN = '\x1b'
END_TOKEN = '\x1c'
931
932


933
def make_token(token: str, argument: str = '') -> str:
934
935
    """
    Turns the ``token`` and ``argument`` into a special token that
936
    will be caught by the `PreprocessorToken`-parser.
937

938
939
    This function is a support function that should be used by
    preprocessors to inject preprocessor tokens into the source text.
940
    """
941
942
943
    assert RX_PREPROCESSOR_TOKEN.match(token)
    assert argument.find(BEGIN_TOKEN) < 0
    assert argument.find(END_TOKEN) < 0
944

945
    return BEGIN_TOKEN + token + argument + END_TOKEN
946
947


948
def nil_preprocessor(text: str) -> str:
Eckhart Arnold's avatar
Eckhart Arnold committed
949
    return text
950
951


952
class PreprocessorToken(Parser):
953
    """
954
    Parses tokens that have been inserted by a preprocessor.
955
    
956
    Preprocessors can generate Tokens with the ``make_token``-function.
957
    These tokens start and end with magic characters that can only be
958
959
960
    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.
961
    """
962

963
964
965
966
    def __init__(self, token: str) -> None:
        assert token and token.isupper()
        assert RX_PREPROCESSOR_TOKEN.match(token)
        super(PreprocessorToken, self).__init__(token)
967

968
    def __call__(self, text: str) -> Tuple[Node, str]:
969
970
        if text[0:1] == BEGIN_TOKEN:
            end = text.find(END_TOKEN, 1)
971
972
            if end < 0:
                node = Node(self, '').add_error(
973
974
                    'END_TOKEN delimiter missing from preprocessor token. '
                    '(Most likely due to a preprocessor bug!)')  # type: Node
975
976
977
                return node, text[1:]
            elif end == 0:
                node = Node(self, '').add_error(
978
979
                    'Preprocessor-token cannot have zero length. '
                    '(Most likely due to a preprocessor bug!)')
980
                return node, text[2:]
981
            elif text.find(BEGIN_TOKEN, 1, end) >= 0:
982
983
                node = Node(self, text[len(self.name) + 1:end])
                node.add_error(
984
985
986
                    'Preprocessor-tokens must not be nested or contain '
                    'BEGIN_TOKEN delimiter as part of their argument. '
                    '(Most likely due to a preprocessor bug!)')
987
988
989
990
991
992
993
994
                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
995
    """Regular expression parser.
996
997
998
999
1000
    
    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
1001
1002
1003
1004
1005
1006
1007
1008

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

    EBNF-Notation:  `/ ... /`
    EBNF-Example:   `word = /\w+/`
1009
    """
1010
1011

    def __init__(self, regexp, name: str = '') -> None:
1012
        super(RegExp, self).__init__(name)
1013
1014
1015
        self.regexp = re.compile(regexp) if isinstance(regexp, str) else regexp

    def __deepcopy__(self, memo):
Eckhart Arnold's avatar
Eckhart Arnold committed
1016
        # `regex` supports deep copies, but not `re`
1017
        try:
Eckhart Arnold's avatar
Eckhart Arnold committed
1018
            regexp = copy.deepcopy(self.regexp, memo)
1019
1020
        except TypeError:
            regexp = self.regexp.pattern
1021
        return RegExp(regexp, self.name)
1022

1023
    def __call__(self, text: str) -> Tuple[Node, str]:
1024
        match = text[0:1] != BEGIN_TOKEN and self.regexp.match(text)  # ESC starts a preprocessor token.
1025
1026
1027
1028
1029
        if match:
            end = match.end()
            return Node(self, text[:end]), text[end:]
        return None, text

1030
    def __repr__(self):
1031
        return '/%s/' % self.regexp.pattern
1032

1033

1034
1035
class Whitespace(RegExp):
    assert WHITESPACE_PTYPE == ":Whitespace"
1036
1037


1038
class RE(Parser):
1039
1040
    """
    Regular Expressions with optional leading or trailing whitespace.
1041
1042
    
    The RE-parser parses pieces of text that match a given regular
Eckhart Arnold's avatar
Eckhart Arnold committed
1043
    expression. Other than the ``RegExp``-Parser it can also skip
1044
1045
    "implicit whitespace" before or after the matched text.
    
Eckhart Arnold's avatar
Eckhart Arnold committed
1046
1047
1048
1049
1050
    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
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065

    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+/~`
1066
    """
1067
    def __init__(self, regexp, wL=None, wR=None, name=''):
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
        """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.
        """
1083
        super(RE, self).__init__(name)
1084
1085
        self.wL = wL
        self.wR = wR
1086
1087
        self.wspLeft = Whitespace(wL) if wL else ZOMBIE_PARSER
        self.wspRight = Whitespace(wR) if wR else ZOMBIE_PARSER
1088
1089
        self.main = RegExp(regexp)

Eckhart Arnold's avatar
Eckhart Arnold committed
1090
1091
1092
1093
1094
    def __deepcopy__(self, memo={}):
        try:
            regexp = copy.deepcopy(self.main.regexp, memo)
        except TypeError:
            regexp = self.main.regexp.pattern
1095
        return self.__class__(regexp, self.wL, self.wR, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
1096

1097
    def __call__(self, text: str) -> Tuple[Node, str]:
1098
        # assert self.main.regexp.pattern != "@"