为了学习Lex / Yacc，我正在按照RFC 4180第3页上指定的语法编写CSV解析器。
我遇到了“减少/减少冲突”，而且我不确定如何前进。我的语法规则1和规则3之间似乎有冲突，但是我不知道有没有其他方法可以在最后一条记录之后描述带有或不带有换行符的CSV。同样，当我删除规则10（空字段规则）时，减少/减少冲突也消失了。但是，我需要处理空字段。
我的语法有什么问题，应该如何纠正？
%token COMMA
%token DQUOTE
%token CRLF
%token TEXTDATA
%%
file: records CRLF
| records;
records: records CRLF record
| record;
record: fields;
fields: fields COMMA field
| field;
field: DQUOTE escaped DQUOTE
| TEXTDATA
| ;
escaped: escaped TEXTDATA
| escaped COMMA
| escaped CRLF
| escaped DQUOTE DQUOTE
| TEXTDATA
| COMMA
| CRLF
| DQUOTE DQUOTE;
yacc -v输出State 14 conflicts: 1 reduce/reduce
Grammar
0 $accept: file $end
1 file: records CRLF
2 | records
3 records: records CRLF record
4 | record
5 record: fields
6 fields: fields COMMA field
7 | field
8 field: DQUOTE escaped DQUOTE
9 | TEXTDATA
10 | /* empty */
11 escaped: escaped TEXTDATA
12 | escaped COMMA
13 | escaped CRLF
14 | escaped DQUOTE DQUOTE
15 | TEXTDATA
16 | COMMA
17 | CRLF
18 | DQUOTE DQUOTE
Terminals, with rules where they appear
$end (0) 0
error (256)
COMMA (258) 6 12 16
DQUOTE (259) 8 14 18
CRLF (260) 1 3 13 17
TEXTDATA (261) 9 11 15
Nonterminals, with rules where they appear
$accept (7)
on left: 0
file (8)
on left: 1 2, on right: 0
records (9)
on left: 3 4, on right: 1 2 3
record (10)
on left: 5, on right: 3 4
fields (11)
on left: 6 7, on right: 5 6
field (12)
on left: 8 9 10, on right: 6 7
escaped (13)
on left: 11 12 13 14 15 16 17 18, on right: 8 11 12 13 14
state 0
0 $accept: . file $end
DQUOTE shift, and go to state 1
TEXTDATA shift, and go to state 2
$default reduce using rule 10 (field)
file go to state 3
records go to state 4
record go to state 5
fields go to state 6
field go to state 7
state 1
8 field: DQUOTE . escaped DQUOTE
COMMA shift, and go to state 8
DQUOTE shift, and go to state 9
CRLF shift, and go to state 10
TEXTDATA shift, and go to state 11
escaped go to state 12
state 2
9 field: TEXTDATA .
$default reduce using rule 9 (field)
state 3
0 $accept: file . $end
$end shift, and go to state 13
state 4
1 file: records . CRLF
2 | records .
3 records: records . CRLF record
CRLF shift, and go to state 14
$default reduce using rule 2 (file)
state 5
4 records: record .
$default reduce using rule 4 (records)
state 6
5 record: fields .
6 fields: fields . COMMA field
COMMA shift, and go to state 15
$default reduce using rule 5 (record)
state 7
7 fields: field .
$default reduce using rule 7 (fields)
state 8
16 escaped: COMMA .
$default reduce using rule 16 (escaped)
state 9
18 escaped: DQUOTE . DQUOTE
DQUOTE shift, and go to state 16
state 10
17 escaped: CRLF .
$default reduce using rule 17 (escaped)
state 11
15 escaped: TEXTDATA .
$default reduce using rule 15 (escaped)
state 12
8 field: DQUOTE escaped . DQUOTE
11 escaped: escaped . TEXTDATA
12 | escaped . COMMA
13 | escaped . CRLF
14 | escaped . DQUOTE DQUOTE
COMMA shift, and go to state 17
DQUOTE shift, and go to state 18
CRLF shift, and go to state 19
TEXTDATA shift, and go to state 20
state 13
0 $accept: file $end .
$default accept
state 14
1 file: records CRLF .
3 records: records CRLF . record
DQUOTE shift, and go to state 1
TEXTDATA shift, and go to state 2
$end reduce using rule 1 (file)
$end [reduce using rule 10 (field)]
$default reduce using rule 10 (field)
record go to state 21
fields go to state 6
field go to state 7
state 15
6 fields: fields COMMA . field
DQUOTE shift, and go to state 1
TEXTDATA shift, and go to state 2
$default reduce using rule 10 (field)
field go to state 22
state 16
18 escaped: DQUOTE DQUOTE .
$default reduce using rule 18 (escaped)
state 17
12 escaped: escaped COMMA .
$default reduce using rule 12 (escaped)
state 18
8 field: DQUOTE escaped DQUOTE .
14 escaped: escaped DQUOTE . DQUOTE
DQUOTE shift, and go to state 23
$default reduce using rule 8 (field)
state 19
13 escaped: escaped CRLF .
$default reduce using rule 13 (escaped)
state 20
11 escaped: escaped TEXTDATA .
$default reduce using rule 11 (escaped)
state 21
3 records: records CRLF record .
$default reduce using rule 3 (records)
state 22
6 fields: fields COMMA field .
$default reduce using rule 6 (fields)
state 23
14 escaped: escaped DQUOTE DQUOTE .
$default reduce using rule 14 (escaped)
[例如，如果输入是TEXTDATA CRLF，则不清楚是导出file -> records CRLF然后将records导出到单个记录，还是不清楚是否应该导出file -> records然后将records导出到两个记录，其中第二个是空的。
为了避免这种歧义，您只需删除records CRLF替代项。以CRLF结尾的文件仍将被接受，但它们将被视为末尾有空记录。
如果这不是您想要的，则需要重写records，以使最后一个记录不允许为空（然后保留file: records CRLF的产生）。