我在ANTLR解析器规则上使用语义谓词时遇到了一些麻烦。这是我的语法,旨在识别几种不同的日期格式:
grammar sample ;
options { language=Python3; }
@parser::header {
from datetime import datetime
}
month_number returns [val] : INTEGER { 1 <= int($INTEGER.text) <= 12 }? {$val = int($INTEGER.text)} ;
day_number returns [val] : INTEGER { 1 <= int($INTEGER.text) <= 31 }? {$val = int($INTEGER.text)} ;
year_4digit returns [val] : INTEGER { 1900 <= int($INTEGER.text) <= 2100 }? {$val = int($INTEGER.text)} ;
year_2digit returns [val] : '\''? INTEGER {(int($INTEGER.text) >= 65 or int($INTEGER.text) < 40)}?
{$val = (1900 + int($INTEGER.text)) if (int($INTEGER.text) >= 65) else (2000 + int($INTEGER.text))} ;
year_digits returns [val]
: year_4digit {$val = $year_4digit.val}
| year_2digit {$val = $year_2digit.val}
;
mdy returns [val]
: month_number '-' day_number '-' year_digits {$val = datetime($year_digits.val, $month_number.val, $day_number.val)}
| month_number '/' day_number '/' year_digits {$val = datetime($year_digits.val, $month_number.val, $day_number.val)}
;
ymd returns [val]
: year_4digit '-' month_number '-' day_number {$val = datetime($year_4digit.val, $month_number.val, $day_number.val)}
| year_4digit '/' month_number '/' day_number {$val = datetime($year_4digit.val, $month_number.val, $day_number.val)}
;
date_as_numbers returns [val]
: ymd {$val = $ymd.val}
| mdy {$val = $mdy.val}
;
INTEGER: '0'..'9'+ ;
我用以下程序测试:
from myPackage.sampleParser import sampleParser
from myPackage.sampleLexer import sampleLexer
from antlr4 import CommonTokenStream
from antlr4 import InputStream
date_input = InputStream("2/12/2017".lower())
lexer = sampleLexer(date_input)
stream = CommonTokenStream(lexer)
parser = sampleParser(stream)
result = parser.date_as_numbers()
print(result.val)
这会导致以下错误:
line 1:1 rule year_4digit failed predicate: { 1900 <= int($INTEGER.text) <= 2100 }?
line 1:9 rule day_number failed predicate: { 1 <= int($INTEGER.text) <= 31 }?
Traceback (most recent call last):
File "/Users/kwilliams/Library/Preferences/IntelliJIdea2017.3/scratches/scratch_1.py", line 11, in <module>
result = parser.date_as_numbers()
File "/Users/kwilliams/git/myPackage/sampleParser.py", line 482, in date_as_numbers
localctx._ymd = self.ymd()
File "/Users/kwilliams/git/myPackage/sampleParser.py", line 436, in ymd
localctx.val = datetime(localctx._year_4digit.val, localctx._month_number.val, localctx._day_number.val)
TypeError: an integer is required (got type NoneType)
所以我认为正在发生的是year_4digit
中的谓词会引发异常,因为数字2
不在其范围内,但无论如何都会返回year_4digit
匹配,尚未填充其val
属性,导致下游错误NoneType
。这是对的吗?
如果是这样 - 什么是好的解决方案?我是否需要将语义谓词放在规则或其他内容的前面?如果这是正确的解决方案,我将如何对INTEGER
令牌进行预测?
(另外 - 我希望能够$INTEGER.int
而不是int($INTEGER.text)
,但也许这在Python目标中不可用?切向和小问题。)
感谢。