yacc: 冲突: 1 reduce/reduce
yacc: conflicts: 1 reduce/reduce
为了学习 Lex/Yacc，我正在按照 RFC 4180 第 3 页指定的语法编写 CSV 解析器。
我 运行 陷入了“reduce/reduce 冲突”，我不确定如何进行。这似乎是我的语法规则 1 和规则 3 之间的冲突，但我不知道在最后一条记录之后有或没有换行符的任何其他方式来描述 CSV。此外，当我删除规则 10（空字段规则）时，reduce/reduce 冲突消失；但是，我需要处理空字段。
我的语法有什么问题，我应该如何纠正它？
Yacc 来源
%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)
如果输入，比如TEXTDATA CRLF，不清楚是先导出file -> records CRLF再导出records到单条记录，还是先导出file -> records 然后将 records 派生为两条记录，其中第二条记录仅包含一个空字段。
为避免这种歧义，您可以删除 records CRLF 替代项。以 CRLF 结尾的文件仍将被接受 - 它们将被视为末尾有一个空字段。
如果这不是你想要的，你需要重写fields，让最后一条记录不允许为空（然后保留file: records CRLF产生）。
PS：顺便说一句，在我看来，您应该将一些解析工作移至词法分析器，特别是解析引用字符串内容的部分。像 "abc" 这样的东西最好通过让词法分析器把它变成一个单一的标记来处理。
为了学习 Lex/Yacc，我正在按照 RFC 4180 第 3 页指定的语法编写 CSV 解析器。
我 运行 陷入了“reduce/reduce 冲突”，我不确定如何进行。这似乎是我的语法规则 1 和规则 3 之间的冲突，但我不知道在最后一条记录之后有或没有换行符的任何其他方式来描述 CSV。此外，当我删除规则 10（空字段规则）时，reduce/reduce 冲突消失；但是，我需要处理空字段。
我的语法有什么问题，我应该如何纠正它？
Yacc 来源
%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)
如果输入，比如TEXTDATA CRLF，不清楚是先导出file -> records CRLF再导出records到单条记录，还是先导出file -> records 然后将 records 派生为两条记录，其中第二条记录仅包含一个空字段。
为避免这种歧义，您可以删除 records CRLF 替代项。以 CRLF 结尾的文件仍将被接受 - 它们将被视为末尾有一个空字段。
如果这不是你想要的，你需要重写fields，让最后一条记录不允许为空（然后保留file: records CRLF产生）。
PS：顺便说一句，在我看来，您应该将一些解析工作移至词法分析器，特别是解析引用字符串内容的部分。像 "abc" 这样的东西最好通过让词法分析器把它变成一个单一的标记来处理。