parse.py 138 KB
Newer Older
1
# parse.py - parser combinators for DHParser
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
#
# Copyright 2016  by Eckhart Arnold (arnold@badw.de)
#                 Bavarian Academy of Sciences an Humanities (badw.de)
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.  See the License for the specific language governing
# permissions and limitations under the License.
Eckhart Arnold's avatar
Eckhart Arnold committed
17

18
19

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

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

32

33
from collections import defaultdict
34
import copy
eckhart's avatar
eckhart committed
35
from typing import Callable, cast, List, Tuple, Set, Dict, \
eckhart's avatar
eckhart committed
36
    DefaultDict, Sequence, Union, Optional
37

eckhart's avatar
eckhart committed
38
from DHParser.configuration import get_config_value
39
40
from DHParser.error import Error, ErrorCode, is_error, MANDATORY_CONTINUATION, \
    LEFT_RECURSION_WARNING, UNDEFINED_RETRIEVE, PARSER_LOOKAHEAD_FAILURE_ONLY, \
eckhart's avatar
eckhart committed
41
    PARSER_LOOKAHEAD_MATCH_ONLY, PARSER_STOPPED_BEFORE_END, PARSER_NEVER_TOUCHES_DOCUMENT, \
42
43
44
    MALFORMED_ERROR_STRING, MANDATORY_CONTINUATION_AT_EOF, DUPLICATE_PARSERS_IN_ALTERNATIVE, \
    CAPTURE_WITHOUT_PARSERNAME, CAPTURE_DROPPED_CONTENT_WARNING, LOOKAHEAD_WITH_OPTIONAL_PARSER, \
    BADLY_NESTED_OPTIONAL_PARSER, BAD_ORDER_OF_ALTERNATIVES, BAD_MANDATORY_SETUP, \
45
    OPTIONAL_REDUNDANTLY_NESTED_WARNING, CAPTURE_STACK_NOT_EMPTY, BAD_REPETITION_COUNT
eckhart's avatar
eckhart committed
46
from DHParser.log import CallItem, HistoryRecord
47
from DHParser.preprocess import BEGIN_TOKEN, END_TOKEN, RX_TOKEN_NAME
48
from DHParser.stringview import StringView, EMPTY_STRING_VIEW
eckhart's avatar
eckhart committed
49
from DHParser.syntaxtree import ChildrenType, Node, RootNode, WHITESPACE_PTYPE, \
50
    TOKEN_PTYPE, ZOMBIE_TAG, EMPTY_NODE, ResultType
51
from DHParser.toolkit import sane_parser_name, escape_control_characters, re, cython, \
52
    abbreviate_middle, RX_NEVER_MATCH, RxPatternType, linebreaks, line_col
53

54
__all__ = ('ParserError',
eckhart's avatar
eckhart committed
55
56
57
           'ApplyFunc',
           'FlagFunc',
           'ParseFunc',
58
           'Parser',
59
           'UnknownParserError',
60
           'AnalysisError',
61
           'GrammarError',
62
           'Grammar',
63
64
           'Always',
           'Never',
eckhart's avatar
eckhart committed
65
           'AnyChar',
66
           'PreprocessorToken',
67
           'Token',
68
           'DropToken',
69
           'RegExp',
70
71
           'RE',
           'TKN',
72
           'Whitespace',
73
           'DropRegExp',
74
           'mixin_comment',
di68kap's avatar
di68kap committed
75
           'mixin_nonempty',
di68kap's avatar
di68kap committed
76
           'CombinedParser',
eckhart's avatar
eckhart committed
77
78
           'UnaryParser',
           'NaryParser',
79
           'Drop',
80
81
82
83
           'Synonym',
           'Option',
           'ZeroOrMore',
           'OneOrMore',
84
           'NO_MANDATORY',
Eckhart Arnold's avatar
Eckhart Arnold committed
85
           'MandatoryNary',
86
87
           'Series',
           'Alternative',
88
           'INFINITE',
89
           'Counted',
90
           'Interleave',
eckhart's avatar
eckhart committed
91
           'Required',
92
93
94
95
96
           'Lookahead',
           'NegativeLookahead',
           'Lookbehind',
           'NegativeLookbehind',
           'last_value',
97
98
           'optional_last_value',
           'matching_bracket',
99
100
101
           'Capture',
           'Retrieve',
           'Pop',
102
           'Forward')
103
104
105
106


########################################################################
#
107
# ParserError class
108
109
110
111
#
########################################################################


Eckhart Arnold's avatar
Eckhart Arnold committed
112
113
114
class ParserError(Exception):
    """
    A `ParserError` is thrown for those parser errors that allow the
115
    controlled re-entrance of the parsing process after the error occurred.
Eckhart Arnold's avatar
Eckhart Arnold committed
116
    If a reentry-rule has been configured for the parser where the error
117
    occurred, the parser guard can resume the parsing process.
Eckhart Arnold's avatar
Eckhart Arnold committed
118
119

    Currently, the only case when a `ParserError` is thrown (and not some
120
    different kind of error like `UnknownParserError`) is when a `Series`-
eckhart's avatar
eckhart committed
121
    or `Interleave`-parser detects a missing mandatory element.
Eckhart Arnold's avatar
Eckhart Arnold committed
122
    """
eckhart's avatar
eckhart committed
123
    def __init__(self, node: Node, rest: StringView, error: Error, first_throw: bool):
eckhart's avatar
eckhart committed
124
        assert node is not None
eckhart's avatar
eckhart committed
125
126
127
        self.node = node    # type: Node
        self.rest = rest    # type: StringView
        self.error = error  # type: Error
128
        self.first_throw = first_throw  # type: bool
eckhart's avatar
eckhart committed
129
        self.frozen_callstack = tuple()  # type: Tuple[CallItem, ...]  # tag_name, location
Eckhart Arnold's avatar
Eckhart Arnold committed
130

131
    def __str__(self):
132
        return "%i: %s    %s" % (self.node.pos, str(self.rest[:25]), repr(self.node))
133

Eckhart Arnold's avatar
Eckhart Arnold committed
134

135
136
137
ResumeList = List[Union[RxPatternType, str, Callable]]  # list of strings or regular expressiones
ReentryPointAlgorithm = Callable[[StringView, int], Tuple[int, int]]
# (text, start point) => (reentry point, match length)
138
# A return value of (-1, x) means that no reentry point before the end of the document was found
Eckhart Arnold's avatar
Eckhart Arnold committed
139
140


eckhart's avatar
eckhart committed
141
@cython.locals(upper_limit=cython.int, closest_match=cython.int, pos=cython.int)
142
143
144
def reentry_point(rest: StringView,
                  rules: ResumeList,
                  comment_regex,
145
                  search_window: int = -1) -> int:
Eckhart Arnold's avatar
Eckhart Arnold committed
146
147
    """
    Finds the point where parsing should resume after a ParserError has been caught.
148
    The algorithm makes sure that this reentry-point does not lie inside a comment.
149
150
151
    The re-entry point is always the point after the end of the match of the regular
    expression defining the re-entry point. (Use look ahead, if you wand to define
    the re-entry point by what follows rather than by what text precedes the point.)
Eckhart Arnold's avatar
Eckhart Arnold committed
152
153
    Args:
        rest:  The rest of the parsed text or, in other words, the point where
154
            a ParserError was thrown.
155
156
        rules: A list of strings, regular expressions or callable, i.e.
            reentry-point-search-functions. The rest of the text is searched for
157
158
            each of these. The closest match is the point where parsing will be
            resumed.
159
        comment_regex: A regular expression object that matches comments.
160
161
        search_window: The maximum size of the search window for finding the
            reentry-point. A value smaller or equal zero means that
Eckhart Arnold's avatar
Eckhart Arnold committed
162
    Returns:
163
164
        The integer index of the closest reentry point or -1 if no reentry-point
        was found.
Eckhart Arnold's avatar
Eckhart Arnold committed
165
    """
166
    upper_limit = len(rest) + 1
167
    closest_match = upper_limit
168
169
    comments = None  # typ: Optional[Iterator]

eckhart's avatar
eckhart committed
170
    @cython.locals(a=cython.int, b=cython.int)
171
172
173
174
175
176
177
178
179
180
181
    def next_comment() -> Tuple[int, int]:
        nonlocal rest, comments
        if comments:
            try:
                m = next(comments)
                a, b = m.span()
                return rest.index(a), rest.index(b)
            except StopIteration:
                comments = None
        return -1, -2

182
183
184
185
    @cython.locals(start=cython.int)
    def str_search(s, start: int = 0) -> Tuple[int, int]:
        nonlocal rest
        return rest.find(s, start, start + search_window), len(s)
186

eckhart's avatar
eckhart committed
187
    @cython.locals(start=cython.int, end=cython.int)
188
189
    def rx_search(rx, start: int = 0) -> Tuple[int, int]:
        nonlocal rest
190
        m = rest.search(rx, start, start + search_window)
191
        if m:
192
193
            begin, end = m.span()
            return rest.index(begin), end - begin
194
195
        return -1, 0

196
197
198
199
    def algorithm_search(func: Callable, start: int = 0):
        nonlocal rest
        return func(rest, start)

eckhart's avatar
eckhart committed
200
    @cython.locals(a=cython.int, b=cython.int, k=cython.int, length=cython.int)
201
202
203
    def entry_point(search_func, search_rule) -> int:
        a, b = next_comment()
        k, length = search_func(search_rule)
eckhart's avatar
eckhart committed
204
        while a < b <= k + length:
205
            a, b = next_comment()
206
207
208
        # find next as long as start or end point of resume regex are inside a comment
        while (a < k < b) or (a < k + length < b):
            k, length = search_func(search_rule, b)
209
210
            while a < b <= k:
                a, b = next_comment()
211
        return k + length if k >= 0 else upper_limit
212

213
    # find closest match
Eckhart Arnold's avatar
Eckhart Arnold committed
214
    for rule in rules:
215
        comments = rest.finditer(comment_regex)
216
217
218
219
220
221
222
        if callable(rule):
            search_func = algorithm_search
        elif isinstance(rule, str):
            search_func = str_search
        else:
            search_func = rx_search
        pos = entry_point(search_func, rule)
223
        closest_match = min(pos, closest_match)
224

225
    # in case no rule matched return -1
226
227
228
    if closest_match == upper_limit:
        closest_match = -1
    return closest_match
Eckhart Arnold's avatar
Eckhart Arnold committed
229
230


231
232
233
234
235
236
237
########################################################################
#
# Parser base class
#
########################################################################


238
239
ApplyFunc = Callable[[List['Parser']], Optional[bool]]
        # The return value of `True` stops any further application
eckhart's avatar
eckhart committed
240
FlagFunc = Callable[[ApplyFunc, Set[ApplyFunc]], bool]
eckhart's avatar
eckhart committed
241
ParseFunc = Callable[[StringView], Tuple[Optional[Node], StringView]]
eckhart's avatar
eckhart committed
242
243


244
class Parser:
245
246
247
248
249
250
251
252
253
254
255
256
257
258
    """
    (Abstract) Base class for Parser combinator parsers. Any parser
    object that is actually used for parsing (i.e. no mock parsers)
    should should be derived from this class.

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

    There are two different types of parsers:

di68kap's avatar
di68kap committed
259
    1. *Named parsers* for which a name is set in field `parser.pname`.
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
       The results produced by these parsers can later be retrieved in
       the AST by the parser name.

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

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

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

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

    Attributes and Properties:
283

284
285
        pname:  The parser's name or a (possibly empty) alias name in case
                of an anonymous parser.
286

287
288
289
290
291
        anonymous: A property indicating that the parser remains anynomous
                anonymous with respect to the nodes it returns. For performance
                reasons this is implemented as an object variable rather
                than a property. This property must always be equal to
                `self.tag_name[0] == ":"`.
292

293
294
295
296
        drop_content: A property (for performance reasons implemented as
                simple field) that, if set, induces the parser not to return
                the parsed content or sub-tree if it has matched but the
                dummy `EMPTY_NODE`. In effect the parsed content will be
297
298
299
                dropped from the concrete syntax tree already. Only
                anonymous (or pseudo-anonymous) parsers are allowed to
                drop content.
300

301
        tag_name: The tag_name for the nodes that are created by
302
303
                the parser. If the parser is named, this is the same as
                `pname`, otherwise it is the name of the parser's type.
304

305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
        visited:  Mapping of places this parser has already been to
                during the current parsing process onto the results the
                parser returned at the respective place. This dictionary
                is used to implement memoizing.

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

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

320
321
322
323
        proxied: The original `_parse()`-method is stored here, if a
                proxy (e.g. a tracing debugger) is installed via the
                `set_proxy()`-method.

324
        _grammar:  A reference to the Grammar object to which the parser
325
                is attached.
326
327
328
329
330

        _symbol:  The name of the closest named parser to which this
                parser is connected in a grammar. If pname is not the
                empty string, this will become the same as pname, when
                the property `symbol` is read for the first time.
331
332
    """

333
    def __init__(self) -> None:
334
        # assert isinstance(name, str), str(name)
335
        self.pname = ''               # type: str
336
        self.anonymous = True         # type: bool
337
        self.drop_content = False     # type: bool
338
339
        self.tag_name = self.ptype    # type: str
        self.cycle_detection = set()  # type: Set[ApplyFunc]
340
        # this indirection is required for Cython-compatibility
341
        self._parse_proxy = self._parse  # type: ParseFunc
eckhart's avatar
eckhart committed
342
        # self.proxied = None           # type: Optional[ParseFunc]
343
344
345
346
        try:
            self._grammar = GRAMMAR_PLACEHOLDER  # type: Grammar
        except NameError:
            pass
347
        self._symbol = ''             # type: str
348
349
350
        self.reset()

    def __deepcopy__(self, memo):
351
        """Deepcopy method of the parser. Upon instantiation of a Grammar-
352
        object, parsers will be deep-copied to the Grammar object. If a
353
        derived parser-class changes the signature of the `__init__`-constructor,
354
355
356
        `__deepcopy__`-method must be replaced (i.e. overridden without
        calling the same method from the superclass) by the derived class.
        """
357
        duplicate = self.__class__()
358
        copy_parser_base_attrs(self, duplicate)
359
        return duplicate
360

361
    def __repr__(self):
di68kap's avatar
di68kap committed
362
        return self.pname + self.ptype
363
364

    def __str__(self):
di68kap's avatar
di68kap committed
365
        return self.pname + (' = ' if self.pname else '') + repr(self)
366

367
368
369
370
371
372
    @property
    def ptype(self) -> str:
        """Returns a type name for the parser. By default this is the name of
        the parser class with an added leading colon ':'. """
        return ':' + self.__class__.__name__

373
374
375
376
377
    @property
    def symbol(self) -> str:
        """Returns the symbol with which the parser is associated in a grammar.
        This is the closest parser with a pname that contains this parser."""
        if not self._symbol:
eckhart's avatar
eckhart committed
378
379
380
381
382
383
            try:
                self._symbol = self.grammar.associated_symbol(self).pname
            except AttributeError:
                # return an empty string, if parser is not connected to grammar,
                # but be sure not to save the empty string in self._symbol
                return ''
384
385
        return self._symbol

386
387
388
    @property
    def repr(self) -> str:
        """Returns the parser's name if it has a name and self.__repr___() otherwise."""
di68kap's avatar
di68kap committed
389
        return self.pname if self.pname else self.__repr__()
390

391
392
393
394
    def reset(self):
        """Initializes or resets any parser variables. If overwritten,
        the `reset()`-method of the parent class must be called from the
        `reset()`-method of the derived class."""
395
        self.visited = dict()  # type: Dict[int, Tuple[Optional[Node], StringView]]
eckhart's avatar
eckhart committed
396
        self.recursion_counter = defaultdict(int)  # type: DefaultDict[int, int]
397

eckhart's avatar
eckhart committed
398
    @cython.locals(location=cython.int, gap=cython.int, i=cython.int)
399
400
401
    def __call__(self: 'Parser', text: StringView) -> Tuple[Optional[Node], StringView]:
        """Applies the parser to the given text. This is a wrapper method that adds
        the business intelligence that is common to all parsers. The actual parsing is
402
403
        done in the overridden method `_parse()`. This wrapper-method can be thought of
        as a "parser guard", because it guards the parsing process.
404
        """
eckhart's avatar
eckhart committed
405
406
407
408
409
410
411
412
        # def get_error_node_id(error_node: Node, root_node: RootNode) -> int:
        #     if error_node:
        #         error_node_id = id(error_node)
        #         while error_node_id not in grammar.tree__.error_nodes and error_node.children:
        #             error_node = error_node.result[-1]
        #             error_node_id = id(error_node)
        #     else:
        #         error_node_id = 0
413

414
        grammar = self._grammar
di68kap's avatar
di68kap committed
415
        location = grammar.document_length__ - text._len  # faster then len(text)?
416
417

        try:
418
419
            # rollback variable changing operation if parser backtracks
            # to a position before the variable changing operation occurred
420
            if grammar.last_rb__loc__ > location:
421
422
                grammar.rollback_to__(location)

423
            # if location has already been visited by the current parser, return saved result
424
425
            visited = self.visited  # using local variable for better performance
            if location in visited:
426
                # no history recording in case of memoized results
427
                return visited[location]
428
429

            # break left recursion at the maximum allowed depth
430
431
432
            left_recursion_depth__ = grammar.left_recursion_depth__
            if left_recursion_depth__:
                if self.recursion_counter[location] > left_recursion_depth__:
433
434
435
436
                    grammar.recursion_locations__.add(location)
                    return None, text
                self.recursion_counter[location] += 1

437
            # finally, the actual parser call!
438
            try:
Eckhart Arnold's avatar
Eckhart Arnold committed
439
                node, rest = self._parse_proxy(text)
440
            except ParserError as pe:
441
                # catching up with parsing after an error occurred
442
                gap = len(text) - len(pe.rest)
di68kap's avatar
di68kap committed
443
                rules = grammar.resume_rules__.get(self.pname, [])
444
                rest = pe.rest[len(pe.node):]
445
446
                i = reentry_point(rest, rules, grammar.comment_rx__,
                                  grammar.reentry_search_window__)
447
                if i >= 0 or self == grammar.start_parser__:
448
                    assert pe.node.children or (not pe.node.result)
449
                    # apply reentry-rule or catch error at root-parser
eckhart's avatar
eckhart committed
450
                    if i < 0:  i = 0
451
                    try:
452
                        zombie = pe.node.pick_child(ZOMBIE_TAG)  # type: Optional[Node]
453
                    except (KeyError, ValueError):
454
455
456
                        zombie = None
                    if zombie and not zombie.result:
                        zombie.result = rest[:i]
eckhart's avatar
eckhart committed
457
                        tail = tuple()  # type: ChildrenType
458
459
                    else:
                        nd = Node(ZOMBIE_TAG, rest[:i]).with_pos(location)
eckhart's avatar
eckhart committed
460
                        # nd.attr['err'] = pe.error.message
461
                        tail = (nd,)
462
                    rest = rest[i:]
463
464
                    if pe.first_throw:
                        node = pe.node
465
                        node.result = node.children + tail
466
                    else:
467
468
                        node = Node(
                            self.tag_name,
di68kap's avatar
di68kap committed
469
470
                            (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) + tail) \
                            .with_pos(location)
471
                elif pe.first_throw:
eckhart's avatar
eckhart committed
472
                    # TODO: Is this case still needed with module "trace"?
473
                    raise ParserError(pe.node, pe.rest, pe.error, first_throw=False)
474
                elif grammar.tree__.errors[-1].code == MANDATORY_CONTINUATION_AT_EOF:
eckhart's avatar
eckhart committed
475
476
                    # try to create tree as faithful as possible
                    node = Node(self.tag_name, pe.node).with_pos(location)
477
                else:
478
479
                    result = (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) if gap \
                        else pe.node  # type: ResultType
480
481
                    raise ParserError(Node(self.tag_name, result).with_pos(location),
                                      text, pe.error, first_throw=False)
482

483
            if left_recursion_depth__:
484
485
486
487
488
489
                self.recursion_counter[location] -= 1
                # don't clear recursion_locations__ !!!

            if node is None:
                # retrieve an earlier match result (from left recursion) if it exists
                if location in grammar.recursion_locations__:
490
491
                    if location in visited:
                        node, rest = visited[location]
492
                        if location != grammar.last_recursion_location__:
493
494
495
                            grammar.tree__.add_error(
                                node, Error("Left recursion encountered. "
                                            "Refactor grammar to avoid slow parsing.",
496
                                            node.pos if node else location,
497
                                            LEFT_RECURSION_WARNING))
eckhart's avatar
eckhart committed
498
                            # error_id = id(node)
499
                            grammar.last_recursion_location__ = location
500
501
502
503
                    # don't overwrite any positive match (i.e. node not None) in the cache
                    # and don't add empty entries for parsers returning from left recursive calls!
                elif grammar.memoization__:
                    # otherwise also cache None-results
504
                    visited[location] = (None, rest)
505
            else:
506
                # assert node._pos < 0 or node == EMPTY_NODE
507
                # if node._pos != EMPTY_NODE:
508
                node._pos = location
509
510
                # assert node._pos >= 0 or node == EMPTY_NODE, \
                #     str("%i < %i" % (grammar.document_length__, location))
511
512
513
514
515
516
                if (grammar.last_rb__loc__ < location
                        and (grammar.memoization__ or location in grammar.recursion_locations__)):
                    # - variable manipulating parsers will not be entered into the cache,
                    #   because caching would interfere with changes of variable state
                    # - in case of left recursion, the first recursive step that
                    #   matches will store its result in the cache
eckhart's avatar
eckhart committed
517
518
                    # TODO: need a unit-test concerning interference of variable manipulation
                    #       and left recursion algorithm?
519
                    visited[location] = (node, rest)
520
521

        except RecursionError:
522
            node = Node(ZOMBIE_TAG, str(text[:min(10, max(1, text.find("\n")))]) + " ...")
523
524
525
526
527
528
            node._pos = location
            grammar.tree__.new_error(node, "maximum recursion depth of parser reached; "
                                           "potentially due to too many errors!")
            rest = EMPTY_STRING_VIEW

        return node, rest
529
530
531
532

    def __add__(self, other: 'Parser') -> 'Series':
        """The + operator generates a series-parser that applies two
        parsers in sequence."""
di68kap's avatar
di68kap committed
533
534
        if isinstance(other, Series):
            return cast('Series', other).__radd__(self)
535
536
537
538
539
540
        return Series(self, other)

    def __or__(self, other: 'Parser') -> 'Alternative':
        """The | operator generates an alternative parser that applies
        the first parser and, if that does not match, the second parser.
        """
di68kap's avatar
di68kap committed
541
542
        if isinstance(other, Alternative):
            return cast('Alternative', other).__ror__(self)
543
544
        return Alternative(self, other)

di68kap's avatar
di68kap committed
545
546
547
548
549
550
551
552
553
    def __mul__(self, other: 'Parser') -> 'Alternative':
        """The * operator generates an interleave parser that applies
        the first parser and the second parser in any possible order
        until both match.
        """
        if isinstance(other, Interleave):
            return cast(Interleave, other).__rmul__(self)
        return Interleave(self, other)

554
555
556
557
558
559
    def _parse(self, text: StringView) -> Tuple[Optional[Node], StringView]:
        """Applies the parser to the given `text` and returns a node with
        the results or None as well as the text at the position right behind
        the matching string."""
        raise NotImplementedError

eckhart's avatar
eckhart committed
560
561
562
563
564
565
566
    def is_optional(self) -> Optional[bool]:
        """Returns `True`, if the parser can never fails, i.e. never yields
        `None`, instead of a node. Returns `False`, if the parser can fail.
        Returns `None` if it is not known whether the parser can fail.
        """
        return None

567
    def set_proxy(self, proxy: Optional[ParseFunc]):
568
569
570
        """Sets a proxy that replaces the _parse()-method. Call `set_proxy`
        with `None` to remove a previously set proxy. Typical use case is
        the installation of a tracing debugger. See module `trace`.
571
572
        """
        if proxy is None:
Eckhart Arnold's avatar
Eckhart Arnold committed
573
            self._parse_proxy = self._parse
574
        else:
eckhart's avatar
eckhart committed
575
576
            if not isinstance(proxy, type(self._parse)):
                # assume that proxy is a function and bind it to self
577
578
                proxy = proxy.__get__(self, type(self))
            else:
eckhart's avatar
eckhart committed
579
                # if proxy is a method it must be a method of self
580
                assert proxy.__self__ == self
Eckhart Arnold's avatar
Eckhart Arnold committed
581
            self._parse_proxy = cast(ParseFunc, proxy)
582

583
    @property
eckhart's avatar
eckhart committed
584
    def grammar(self) -> 'Grammar':
585
586
587
588
589
        try:
            if self._grammar != GRAMMAR_PLACEHOLDER:
                return self._grammar
            else:
                raise AssertionError('Grammar has not yet been set!')
590
591
        except (AttributeError, NameError):
            raise AttributeError('Parser placeholder does not have a grammar!')
592
593
594

    @grammar.setter
    def grammar(self, grammar: 'Grammar'):
595
596
597
598
599
        try:
            if self._grammar == GRAMMAR_PLACEHOLDER:
                self._grammar = grammar
                # self._grammar_assigned_notifier()
            elif self._grammar != grammar:
eckhart's avatar
eckhart committed
600
601
                raise AssertionError("Parser has already been assigned"
                                     "to a different Grammar object!")
602
603
        except AttributeError:
            pass  # ignore setting of grammar attribute for placeholder parser
604
605
        except NameError:  # Cython: No access to GRAMMA_PLACEHOLDER, yet :-(
            self._grammar = grammar
606

eckhart's avatar
eckhart committed
607
    def sub_parsers(self) -> Tuple['Parser', ...]:
608
609
610
        """Returns the list of sub-parsers if there are any.
        Overridden by Unary, Nary and Forward.
        """
eckhart's avatar
eckhart committed
611
        return tuple()
612

613
    def _apply(self, func: ApplyFunc, context: List['Parser'], flip: FlagFunc) -> bool:
614
615
        """
        Applies function `func(parser)` recursively to this parser and all
616
617
        descendant parsers as long as `func()` returns `None` or `False`.
        Otherwise stops the further application of `func` and returns `True`.
eckhart's avatar
eckhart committed
618
619
620
621
622
623
624
625

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

        This is a protected function and should not called from outside
        class Parser or any of its descendants. The entry point for external
        calls is the method `apply()` without underscore!
626
        """
627
628
        if not flip(func, self.cycle_detection):
            if func(context + [self]):
629
630
631
                return True
            else:
                for parser in self.sub_parsers():
632
                    if parser._apply(func, context + [self], flip):
633
634
635
                        return True
                return False
        return False
636

637
    def apply(self, func: ApplyFunc) -> bool:
eckhart's avatar
eckhart committed
638
639
        """
        Applies function `func(parser)` recursively to this parser and all
640
641
642
643
644
645
646
647
648
649
650
651
652
653
        descendant parsers as long as `func()` returns `None` or `False`.
        Traversal is pre-order. Stops the further application of `func` and
        returns `True` once `func` has returned `True`.

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

        This use of the return value allows to use the `apply`-method both
        to issue tests on all descendant parsers (including self) which may be
        decided already after some parsers have been visited without any need
        to visit further parsers. At the same time `apply` can be used to simply
        `apply` a procedure to all descendant parsers (including self) without
        worrying about forgetting the return value of procedure, because a
        return value of `None` means "carry on".
eckhart's avatar
eckhart committed
654
        """
Eckhart Arnold's avatar
Eckhart Arnold committed
655
        def positive_flip(f: Callable[['Parser'], None], flagged: Set[Callable]) -> bool:
eckhart's avatar
eckhart committed
656
657
658
659
660
661
662
663
664
            """Returns True, if function `f` has already been applied to this
            parser and sets the flag accordingly. Interprets `f in flagged == True`
            as meaning that `f` has already been applied."""
            if f in flagged:
                return True
            else:
                flagged.add(f)
                return False

Eckhart Arnold's avatar
Eckhart Arnold committed
665
        def negative_flip(f: Callable[['Parser'], None], flagged: Set[Callable]) -> bool:
eckhart's avatar
eckhart committed
666
667
668
669
670
671
672
673
674
675
            """Returns True, if function `f` has already been applied to this
            parser and sets the flag accordingly. Interprets `f in flagged == False`
            as meaning that `f` has already been applied."""
            if f not in flagged:
                return True
            else:
                flagged.remove(f)
                return False

        if func in self.cycle_detection:
676
            return self._apply(func, [], negative_flip)
eckhart's avatar
eckhart committed
677
        else:
678
            return self._apply(func, [], positive_flip)
679

680
    def static_error(self, msg: str, code: ErrorCode) -> 'AnalysisError':
681
        return (self.symbol, self, Error(msg, 0, code))
682

eckhart's avatar
eckhart committed
683
    def static_analysis(self) -> List['AnalysisError']:
684
685
        """Analyses the parser for logical errors after the grammar has been
        instantiated."""
eckhart's avatar
eckhart committed
686
        return []
eckhart's avatar
eckhart committed
687

688

689
690
def copy_parser_base_attrs(src: Parser, duplicate: Parser):
    """Duplicates all attributes of the Parser-class from source to dest."""
Eckhart Arnold's avatar
Eckhart Arnold committed
691
692
693
694
695
696
    duplicate.pname = src.pname
    duplicate.anonymous = src.anonymous
    duplicate.drop_content = src.drop_content
    duplicate.tag_name = src.tag_name


eckhart's avatar
eckhart committed
697
698
def Drop(parser: Parser) -> Parser:
    """Returns the parser with the `parser.drop_content`-property set to `True`."""
Eckhart Arnold's avatar
Eckhart Arnold committed
699
    assert parser.anonymous, "Parser must be anonymous to be allowed to drop ist content."
eckhart's avatar
eckhart committed
700
701
702
    if isinstance(parser, Forward):
        cast(Forward, parser).parser.drop_content = True
    parser.drop_content = True
Eckhart Arnold's avatar
Eckhart Arnold committed
703
    return parser
eckhart's avatar
eckhart committed
704
705


706
PARSER_PLACEHOLDER = Parser()
707
708


eckhart's avatar
eckhart committed
709
710
711
712
713
def is_parser_placeholder(parser: Optional[Parser]) -> bool:
    """Returns True, if `parser` is `None` or merely a placeholder for a parser."""
    return not parser or parser.ptype == ":Parser"


714
715
716
717
718
719
########################################################################
#
# Grammar class, central administration of all parser of a grammar
#
########################################################################

720
721
def mixin_comment(whitespace: str, comment: str) -> str:
    """
722
    Returns a regular expression pattern that merges comment and whitespace
723
    regexps. Thus comments can occur wherever whitespace is allowed
724
725
726
727
728
729
    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).
    """
730
    if comment:
eckhart's avatar
eckhart committed
731
732
        whitespace = '(?:' + whitespace + ')'
        comment = '(?:' + comment + ')'
733
734
        return '(?:' + whitespace + '(?:' + comment + whitespace + ')*)'
    return whitespace
735
736


di68kap's avatar
di68kap committed
737
def mixin_nonempty(whitespace: str) -> str:
Eckhart Arnold's avatar
Eckhart Arnold committed
738
    r"""
739
740
741
    Returns a regular expression pattern that matches only if the regular
    expression pattern `whitespace` matches AND if the match is not empty.

di68kap's avatar
di68kap committed
742
743
    If `whitespace`  does not match the empty string '', anyway,
    then it will be returned unaltered.
744
745
746
747
748
749
750
751
752

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

    In particular, it does not work for fixed size regular expressions,
    that ist / / or /   / or /\t/ won't work, but / */ or /\s*/ or /\s+/
    do work. There is no test for this. Fixed sizes regular expressions
    run through `non_empty_ws` will not match at any more if they are applied
Eckhart Arnold's avatar
Eckhart Arnold committed
753
754
755
756
757
    to the beginning or the middle of a sequence of whitespaces!

    In order to be safe, you whitespace regular expressions should follow
    the rule: "Whitespace cannot be followed by whitespace" or "Either
    grab it all or leave it all".
758
759
760
761
762
763
764
765
766
767

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


768
class UnknownParserError(KeyError):
eckhart's avatar
eckhart committed
769
    """UnknownParserError is raised if a Grammar object is called with a
770
    parser that does not exist or if in the course of parsing a parser
eckhart's avatar
eckhart committed
771
    is referred to that does not exist."""
772
773


774
775
AnalysisError = Tuple[str, Parser, Error]      # pname, parser, error
# TODO: replace with a named tuple?
776
777
778
779
780
781


class GrammarError(Exception):
    """GrammarError will be raised if static analysis reveals errors
    in the grammar.
    """
782
    def __init__(self, static_analysis_result: List[AnalysisError]):
783
784
785
786
787
788
789
790
791
792
        assert static_analysis_result  # must not be empty
        self.errors = static_analysis_result

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


793
794
795
796
797
798
799
800
801
802
803
804
805
class Grammar:
    r"""
    Class Grammar directs the parsing process and stores global state
    information of the parsers, i.e. state information that is shared
    accross parsers.

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

eckhart's avatar
eckhart committed
806
    Example for direct instantiation of a grammar::
807

808
        >>> number = RE(r'\d+') + RE(r'\.') + RE(r'\d+') | RE(r'\d+')
809
810
811
812
813
814
815
816
817
818
819
820
821
822
        >>> number_parser = Grammar(number)
        >>> number_parser("3.1416").content
        '3.1416'

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

    1. It keeps the namespace clean.

    2. The parser names of named parsers do not need to be passed to the
       constructor of the Parser object explicitly, but it suffices to
       assign them to class variables, which results in better
       readability of the Python code.
823
       See classmethod `Grammar._assign_parser_names__()`
824
825

    3. The parsers in the class do not necessarily need to be connected
826
827
       to one single root parser, which is helpful for testing and when
       building up a parser gradually from several components.
828
829
830
831
832
833
834

    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.

835
    Example::
836
837
838
839
840
841
842
843
844

        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+')
845
846
847
            factor = INTEGER | TKN("(") + expression + TKN(")")
            term = factor + ZeroOrMore((TKN("*") | TKN("/")) + factor)
            expression.set(term + ZeroOrMore((TKN("+") | TKN("-")) + term))
848
849
850
851
            root__ = expression

    Upon instantiation the parser objects are deep-copied to the
    Grammar object and assigned to object variables of the same name.
852
853
854
855
856
    For any parser that is directly assigned to a class variable the
    field `parser.pname` contains the variable name after instantiation
    of the Grammar class. The parser will never the less remain anonymous
    with respect to the tag names of the nodes it generates, if its name
    is matched by the `anonymous__` regular expression.
857
    If one and the same parser is assigned to several class variables
858
    such as, for example, the parser `expression` in the example above,
859
    which is also assigned to `root__`, the first name sticks.
860
861
862
863
864
865
866
867
868
869
870
871

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

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

872
    Class Attributes:
873
874
875
876
        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.
877

878
879
880
        resume_rules__: A mapping of parser names to a list of regular expressions
                that act as rules to find the reentry point if a ParserError was
                thrown during the execution of the parser with the respective name.
Eckhart Arnold's avatar
Eckhart Arnold committed
881

882
883
884
885
886
        anonymous__: A regular expression to identify names of parsers that are
                assigned to class fields but shall never the less yield anonymous
                nodes (i.e. nodes the tag name of which starts with a colon ":"
                followed by the parser's class name). The default is to treat all
                parsers starting with an underscore as anonymous in addition to those
887
888
                parsers that are not directly assigned to a class field.

eckhart's avatar
eckhart committed
889
        parser_initialization__:  Before the grammar class (!) has been initialized,
890
                 which happens upon the first time it is instantiated (see
891
                 `:func:_assign_parser_names()` for an explanation), this class
892
893
                 field contains a value other than "done". A value of "done" indicates
                 that the class has already been initialized.
894

895
896
897
898
899
900
901
        static_analysis_pending__: True as long as no static analysis (see the method
                with the same name for more information) has been done to check
                parser tree for correctness. Static analysis
                is done at instantiation and the flag is then set to false, but it
                can also be carried out once the class has been generated
                (by DHParser.ebnf.EBNFCompiler) and then be set to false in the
                definition of the grammar class already.
902

903
904
905
        static_analysis_errors__: A list of errors and warnings that were found in the
                static analysis

eckhart's avatar
eckhart committed
906
907
908
909
        python__src__:  For the purpose of debugging and inspection, this field can
                 take the python src of the concrete grammar class
                 (see `dsl.grammar_provider`).

910
    Instance Attributes:
911
912
        all_parsers__:  A set of all parsers connected to this grammar object

913
914
        comment_rx__:  The compiled regular expression for comments. If no
                comments have been defined, it defaults to RX_NEVER_MATCH
915
916
                This instance-attribute will only be defined if a class-attribute
                with the same name does not already exist!
917

eckhart's avatar
eckhart committed
918
919
920
921
        start_parser__:  During parsing, the parser with which the parsing process
                was started (see method `__call__`) or `None` if no parsing process
                is running.

922
923
924
925
926
927
928
        _dirty_flag__:  A flag indicating that the Grammar has been called at
                least once so that the parsing-variables need to be reset
                when it is called again.

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

eckhart's avatar
eckhart committed
929
930
        document_length__:  the length of the document.

931
932
        document_lbreaks__ (property):  list of linebreaks within the document,
                starting with -1 and ending with EOF. This helps generating line
933
                and column number for history recording and will only be
934
                initialized if :attr:`history_tracking__` is true.
935

936
937
938
939
940
        tree__: The root-node of the parsing tree. This variable is available
               for error-reporting already during parsing  via
               ``self.grammar.tree__.add_error``, but it references the full
               parsing tree only after parsing has been finished.

941
        _reversed__:  the same text in reverse order - needed by the `Lookbehind`-
942
943
944
                parsers.

        variables__:  A mapping for variable names to a stack of their respective
945
946
                string values - needed by the :class:`Capture`-, :class:`Retrieve`-
                and :class:`Pop`-parsers.
947
948

        rollback__:  A list of tuples (location, rollback-function) that are
949
950
951
952
                deposited by the :class:`Capture`- and :class:`Pop`-parsers.
                If the parsing process reaches a dead end then all
                rollback-functions up to the point to which it retreats will be
                called and the state of the variable stack restored accordingly.
953
954
955

        last_rb__loc__:  The last, i.e. most advanced location in the text
                where a variable changing operation occurred. If the parser
956
957
                backtracks to a location at or before last_rb__loc__ (i.e.
                location <= last_rb__loc__) then a rollback of all variable
958
959
                changing operations is necessary that occurred after the
                location to which the parser backtracks. This is done by
960
                calling method :func:`rollback_to__(location)`.
961

962
963
964
965
966
967
968
969
970
971
972
973
974
975
        recursion_locations__:  Stores the locations where left recursion was
                detected. Needed to provide minimal memoization for the left
                recursion detection algorithm, but, strictly speaking, superfluous
                if full memoization is enabled. (See :func:`Parser.__call__()`)

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

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

976
977
978
979
980
981
982
983
984
985
986
        # mirrored class attributes:

        static_analysis_pending__: A pointer to the class attribute of the same name.
                (See the description above.) If the class is instantiated with a
                parser, this pointer will be overwritten with an instance variable
                that serves the same function.

        static_analysis_errors__: A pointer to the class attribute of the same name.
                (See the description above.) If the class is instantiated with a
                parser, this pointer will be overwritten with an instance variable
                that serves the same function.
987
988
989
990
991
992
993
994
995
996
997
998
999
1000

        # tracing and debugging support

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

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

        resume_notices__: A flag indicating that resume messages are generated