python-lark-parser缩进DSL和多行文档字符串
作者：互联网
我正在尝试使用lark实现记录定义DSL.它基于缩进,这会使事情变得更加复杂.
云雀是一个很好的工具,但是我面临一些困难.
这是我正在实现的DSL的代码段：
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
^
我无法理解缩进语法更复杂,而云雀似乎更容易,但是在这里找不到错误.
PS：我也尝试过pyparsing,但在这种情况下却没有成功,考虑到可能需要的代码量,我很难改用PLY.
解决方法:
该错误来自错误放置的_NEWLINE终端.通常,建议根据规则在语法中的作用来确保规则的平衡.因此,这是您应该如何定义element_doc的方法：
?element_doc: ":" _NEWLINE _INDENT multiline_doc _DEDENT
| inline_doc _NEWLINE
请注意添加的换行符,这意味着无论解析器采用两个选项中的哪一个,它都将在语法上以相似的状态结束(_DEDENT也与换行符匹配).
由于第一个变化,第二个变化是：
attribute_simple_type: attribute_name simple_type (element_doc|_NEWLINE)
由于element_doc已经可以处理换行符,因此我们不应尝试对其进行两次匹配.
标签：grammar,lark-parser,python,parsing 来源： https://codeday.me/bug/20191108/2006587.html