符號(hào)表
| 用途 | 符號(hào)表示 |
|---|---|
| 定義 | = |
| 串接 | , |
| 終止 | ; |
| 分隔 | | |
| 可選 | [ ... ] |
| 重復(fù) | { ... } |
| 分組 | ( ... ) |
| 雙引號(hào) | " ... " |
| 單引號(hào) | ' ... ' |
| 注釋 | (* ... *) |
| 特殊序列 | ? ... ? |
| 除外 | - |
Lark預(yù)定義EBNF
//unicode.lark
//
// Whitespace unicode
//
WS_INLINE: /[ \t\xa0]/+
WS: /[ \t\xa0\f\r\n]/+
//common.lark
//
// Whitespace
//
WS_INLINE: (" "|/\t/)+
WS: /[ \t\f\r\n]/+
CR : /\r/
LF : /\n/
NEWLINE: (CR? LF)+
//
// Numbers
//
DIGIT: "0".."9"
HEXDIGIT: "a".."f"|"A".."F"|DIGIT
INT: DIGIT+
SIGNED_INT: ["+"|"-"] INT
DECIMAL: INT "." INT? | "." INT
// float = /-?\d+(\.\d+)?([eE][+-]?\d+)?/
_EXP: ("e"|"E") SIGNED_INT
FLOAT: INT _EXP | DECIMAL _EXP?
SIGNED_FLOAT: ["+"|"-"] FLOAT
NUMBER: FLOAT | INT
SIGNED_NUMBER: ["+"|"-"] NUMBER
//
// Strings
//
_STRING_INNER: /.*?/
_STRING_ESC_INNER: _STRING_INNER /(?<!\\)(\\\\)*?/
ESCAPED_STRING : "\"" _STRING_ESC_INNER "\""
//
// Names (Variables)
//
LCASE_LETTER: "a".."z"
UCASE_LETTER: "A".."Z"
LETTER: UCASE_LETTER | LCASE_LETTER
WORD: LETTER+
CNAME: ("_"|LETTER) ("_"|LETTER|DIGIT)*
// Comments
SH_COMMENT: /#[^\n]*/
CPP_COMMENT: /\/\/[^\n]*/
C_COMMENT: "/*" /(.|\n)*?/ "*/"
SQL_COMMENT: /--[^\n]*/
實(shí)踐
from lark import Lark
l = Lark('''ttt: WORD "," WORD "!"
%import common.WORD // imports from terminal library
%ignore " " // Disregard spaces in text
''',start="ttt")
l.parse("Hello, World!")
from lark import Lark
parser = Lark(r"""
start: _NL? section+
section: "[" NAME "]" _NL item+
item: NAME "=" VALUE? _NL
NAME: /\w/+
VALUE: /./+
%import common.NEWLINE -> _NL
%import common.WS_INLINE
%ignore WS_INLINE
""", parser="lalr")
sample_conf = """
[bla]
a=Hello
this="that",4
empty=
"""
print(parser.parse(sample_conf).pretty())
題外話
與jinja2完美結(jié)合棚点，一個(gè)解析文件冲甘，一個(gè)寫文件；
