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我正在尝试使用lark实现记录定义 DSL 。它基于缩进，这使事情变得更加复杂。

Lark 是一个很棒的工具，但我面临一些困难。

这是我正在实现的 DSL 的一个片段：

record Order :
    """Order record documentation
    should have arbitrary size"""

    field1 Int
    field2 Datetime:
        """Attributes should also have
        multiline documentation"""

    field3 String "inline documentation also works"

这是使用的语法：

?start: (_NEWLINE | redorddef)*

simple_type: NAME

multiline_doc:  MULTILINE_STRING _NEWLINE
inline_doc: INLINE_STRING

?element_doc:  ":" _NEWLINE _INDENT multiline_doc _DEDENT | inline_doc

attribute_name: NAME
attribute_simple_type: attribute_name simple_type [element_doc] _NEWLINE
attributes: attribute_simple_type+
_recordbody: _NEWLINE _INDENT [multiline_doc] attributes _DEDENT
redorddef: "record" NAME ":" _recordbody



MULTILINE_STRING: /"""([^"\\]*(\\.[^"\\]*)*)"""/
INLINE_STRING: /"([^"\\]*(\\.[^"\\]*)*)"/

_WS_INLINE: (" "|/\t/)+
COMMENT: /#[^\n]*/
_NEWLINE: ( /\r?\n[\t ]*/ | COMMENT )+

%import common.CNAME -> NAME
%import common.INT

%ignore /[\t \f]+/  // WS
%ignore /\\[\t \f]*\r?\n/   // LINE_CONT
%ignore COMMENT
%declare _INDENT _DEDENT

它适用于记录定义的多行字符串文档，适用于内联属性定义，但不适用于属性多行字符串文档。

我用来执行的代码是这样的：

import sys
import pprint

from pathlib import Path

from lark import Lark, UnexpectedInput
from lark.indenter import Indenter

scheman_data_works = '''
record Order :
        """Order record documentation
        should have arbitrary size"""

        field1 Int
        # field2 Datetime:
        #   """Attributes should also have
        #   multiline documentation"""

        field3 String "inline documentation also works"
'''

scheman_data_wrong = '''
record Order :
        """Order record documentation
        should have arbitrary size"""

        field1 Int
        field2 Datetime:
                """Attributes should also have
                multiline documentation"""

        field3 String "inline documentation also works"
'''
grammar = r'''

?start: (_NEWLINE | redorddef)*

simple_type: NAME

multiline_doc:  MULTILINE_STRING _NEWLINE
inline_doc: INLINE_STRING

?element_doc:  ":" _NEWLINE _INDENT multiline_doc _DEDENT | inline_doc

attribute_name: NAME
attribute_simple_type: attribute_name simple_type [element_doc] _NEWLINE
attributes: attribute_simple_type+
_recordbody: _NEWLINE _INDENT [multiline_doc] attributes _DEDENT
redorddef: "record" NAME ":" _recordbody



MULTILINE_STRING: /"""([^"\\]*(\\.[^"\\]*)*)"""/
INLINE_STRING: /"([^"\\]*(\\.[^"\\]*)*)"/

_WS_INLINE: (" "|/\t/)+
COMMENT: /#[^\n]*/
_NEWLINE: ( /\r?\n[\t ]*/ | COMMENT )+

%import common.CNAME -> NAME
%import common.INT

%ignore /[\t \f]+/  // WS
%ignore /\\[\t \f]*\r?\n/   // LINE_CONT
%ignore COMMENT
%declare _INDENT _DEDENT

'''

class SchemanIndenter(Indenter):
    NL_type = '_NEWLINE'
    OPEN_PAREN_types = ['LPAR', 'LSQB', 'LBRACE']
    CLOSE_PAREN_types = ['RPAR', 'RSQB', 'RBRACE']
    INDENT_type = '_INDENT'
    DEDENT_type = '_DEDENT'
    tab_len = 4

scheman_parser = Lark(grammar, parser='lalr', postlex=SchemanIndenter())
print(scheman_parser.parse(scheman_data_works).pretty())
print("\n\n")
print(scheman_parser.parse(scheman_data_wrong).pretty())

结果是：

redorddef
Order
multiline_doc """Order record documentation
        should have arbitrary size"""
attributes
    attribute_simple_type
    attribute_name    field1
    simple_type       Int
    attribute_simple_type
    attribute_name    field3
    simple_type       String
    inline_doc        "inline documentation also works"




Traceback (most recent call last):
File "schema_parser.py", line 83, in <module>
    print(scheman_parser.parse(scheman_data_wrong).pretty())
File "/Users/branquif/Dropbox/swf_projects/schema-manager/.venv/lib/python3.7/site-packages/lark/lark.py", line 228, in parse
    return self.parser.parse(text)
File "/Users/branquif/Dropbox/swf_projects/schema-manager/.venv/lib/python3.7/site-packages/lark/parser_frontends.py", line 38, in parse
    return self.parser.parse(token_stream, *[sps] if sps is not NotImplemented else [])
File "/Users/branquif/Dropbox/swf_projects/schema-manager/.venv/lib/python3.7/site-packages/lark/parsers/lalr_parser.py", line 68, in parse
    for token in stream:
File "/Users/branquif/Dropbox/swf_projects/schema-manager/.venv/lib/python3.7/site-packages/lark/indenter.py", line 31, in process
    for token in stream:
File "/Users/branquif/Dropbox/swf_projects/schema-manager/.venv/lib/python3.7/site-packages/lark/lexer.py", line 319, in lex
    for x in l.lex(stream, self.root_lexer.newline_types, self.root_lexer.ignore_types):
File "/Users/branquif/Dropbox/swf_projects/schema-manager/.venv/lib/python3.7/site-packages/lark/lexer.py", line 167, in lex
    raise UnexpectedCharacters(stream, line_ctr.char_pos, line_ctr.line, line_ctr.column, state=self.state)
lark.exceptions.UnexpectedCharacters: No terminal defined for 'f' at line 11 col 2

        field3 String "inline documentation also
^

我不明白缩进语法更复杂，而 Lark 似乎使它更容易，但在这里找不到错误。

PS：我也尝试了 pyparsing，但在同样的情况下没有成功，考虑到可能需要的代码量，我很难转向 PLY。

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2 回答 2

4

该错误来自错位的 _NEWLINE 终端。一般来说，建议确保规则是平衡的，就其在语法中的作用而言。所以这就是你应该如何定义的element_doc：

?element_doc:  ":" _NEWLINE _INDENT multiline_doc _DEDENT
            | inline_doc _NEWLINE

注意添加的换行符，这意味着无论解析器采用两个选项中的哪一个，它都以类似的状态结束，语法方面（_DEDENT也匹配换行符）。

作为第一个变化的结果，第二个变化是：

attribute_simple_type: attribute_name simple_type (element_doc|_NEWLINE)

由于element_doc已经处理换行符，我们不应该尝试匹配它两次。

于 2019-02-13T14:26:40.607 回答
0

您提到尝试 pyparsing，否则我会不理会您的问题。

pyparsing 对空格敏感的解析不是很好，但它确实在这种情况下做出了努力，使用pyparsing.indentedBlock. 写这篇文章有一定程度的痛苦，但可以做到。

import pyparsing as pp

COLON = pp.Suppress(':')
tpl_quoted_string = pp.QuotedString('"""', multiline=True) | pp.QuotedString("'''", multiline=True)
quoted_string = pp.ungroup(tpl_quoted_string | pp.quotedString().addParseAction(pp.removeQuotes))
RECORD = pp.Keyword("record")
ident = pp.pyparsing_common.identifier()

field_expr = (ident("name")
              + ident("type") + pp.Optional(COLON)
              + pp.Optional(quoted_string)("docstring"))

indent_stack = []
STACK_RESET = pp.Empty()
def reset_indent_stack(s, l, t):
    indent_stack[:] = [pp.col(l, s)]
STACK_RESET.addParseAction(reset_indent_stack)

record_expr = pp.Group(STACK_RESET
                       + RECORD - ident("name") + COLON + pp.Optional(quoted_string)("docstring")
                       + (pp.indentedBlock(field_expr, indent_stack))("fields"))

record_expr.ignore(pp.pythonStyleComment)

如果您的示例被写入变量“样本”，请执行以下操作：

print(record_expr.parseString(sample).dump())

并得到：

[['record', 'Order', 'Order record documentation\n    should have arbitrary size', [['field1', 'Int'], ['field2', 'Datetime', 'Attributes should also have\n        multiline documentation'], ['field3', 'String', 'inline documentation also works']]]]
[0]:
  ['record', 'Order', 'Order record documentation\n    should have arbitrary size', [['field1', 'Int'], ['field2', 'Datetime', 'Attributes should also have\n        multiline documentation'], ['field3', 'String', 'inline documentation also works']]]
  - docstring: 'Order record documentation\n    should have arbitrary size'
  - fields: [['field1', 'Int'], ['field2', 'Datetime', 'Attributes should also have\n        multiline documentation'], ['field3', 'String', 'inline documentation also works']]
    [0]:
      ['field1', 'Int']
      - name: 'field1'
      - type: 'Int'
    [1]:
      ['field2', 'Datetime', 'Attributes should also have\n        multiline documentation']
      - docstring: 'Attributes should also have\n        multiline documentation'
      - name: 'field2'
      - type: 'Datetime'
    [2]:
      ['field3', 'String', 'inline documentation also works']
      - docstring: 'inline documentation also works'
      - name: 'field3'
      - type: 'String'
  - name: 'Order'
于 2019-02-13T19:03:43.240 回答