我在状态19有1次转移/减少冲突。我认为标识符＆＃39;的不同出现可能存在问题。但是我很难理解野牛报告并解决冲突。下面是我的语法，然后是带有州信息的野牛报告：
%{
#include <cstdio>
#include <iostream>
using namespace std;
extern "C" int yylex();
extern "C" int yyparse();
void yyerror(const char *s);
%}
%union{
int int_val;
double d_val;
char *strng;
}
%token TLINEC TBLOCKC TPRINT
%token TASSIGN TCPA TOB TCB TCOMMA TSEMIC
%token TIF TELSE TFOR
%token TINT TFLOAT TD TCHAR
%token TPLUS TMINUS TDIV TMULT
%token TLT TGT TAND TOR TEQUAL TNE
%token<int_val> TINTEGER
%token<d_val> TDOUBLE
%token<strng> TID
%token TOPA
%start program
%%
program : command_list
command_list : declaration
| command_list declaration
declaration : function_dec
| variable_dec
| expression
variable_dec : type identifier TSEMIC
| type assignment TSEMIC
assignment : identifier TASSIGN expression
var_list : expression
| var_list TCOMMA expression
|
function_dec : type identifier TOPA p_list TCPA scope
p_list : variable_dec
| p_list TCOMMA variable_dec
type : TINT
| TD
| TFLOAT
| TCHAR
/* inside function scope */
scope : TOB command_list TCB
| TOB TCB
function_call : identifier TOPA var_list TCPA TSEMIC
/* expression rules */
expression : assignment
| function_call
| TOPA expression TCPA
| constant arithmetic_op expression
| constant logical_op expression
| constant
constant : identifier
| num
identifier : TID
num : TINTEGER
| TDOUBLE
arithmetic_op : TPLUS | TMINUS | TDIV | TMULT
logical_op : TLT | TGT | TAND | TOR | TEQUAL | TNE
%%
int main(int, char**){
int y=0;
do{
y=yyparse();
}while(y);
}
void yyerror(const char *s){
cout << "parse error! Message: " << s << endl;
exit(-1);
}
野牛报告：
State 19 conflicts: 1 shift/reduce
Grammar
0 $accept: program $end
1 program: command_list
2 command_list: declaration
3 | command_list declaration
4 declaration: function_dec
5 | variable_dec
6 | expression
7 variable_dec: type identifier TSEMIC
8 | type assignment TSEMIC
9 assignment: identifier TASSIGN expression
10 var_list: expression
11 | var_list TCOMMA expression
12 | /* empty */
13 function_dec: type identifier TOPA p_list TCPA scope
14 p_list: variable_dec
15 | p_list TCOMMA variable_dec
16 type: TINT
17 | TD
18 | TFLOAT
19 | TCHAR
20 scope: TOB command_list TCB
21 | TOB TCB
22 function_call: identifier TOPA var_list TCPA TSEMIC
23 expression: assignment
24 | function_call
25 | TOPA expression TCPA
26 | constant arithmetic_op expression
27 | constant logical_op expression
28 | constant
29 constant: identifier
30 | num
31 identifier: TID
32 num: TINTEGER
33 | TDOUBLE
34 arithmetic_op: TPLUS
35 | TMINUS
36 | TDIV
37 | TMULT
38 logical_op: TLT
39 | TGT
40 | TAND
41 | TOR
42 | TEQUAL
43 | TNE
Terminals, with rules where they appear
$end (0) 0
error (256)
TLINEC (258)
TBLOCKC (259)
TPRINT (260)
TASSIGN (261) 9
TCPA (262) 13 22 25
TOB (263) 20 21
TCB (264) 20 21
TCOMMA (265) 11 15
TSEMIC (266) 7 8 22
TIF (267)
TELSE (268)
TFOR (269)
TINT (270) 16
TFLOAT (271) 18
TD (272) 17
TCHAR (273) 19
TPLUS (274) 34
TMINUS (275) 35
TDIV (276) 36
TMULT (277) 37
TLT (278) 38
TGT (279) 39
TAND (280) 40
TOR (281) 41
TEQUAL (282) 42
TNE (283) 43
TINTEGER (284) 32
TDOUBLE (285) 33
TID (286) 31
TOPA (287) 13 22 25
Nonterminals, with rules where they appear
$accept (33)
on left: 0
program (34)
on left: 1, on right: 0
command_list (35)
on left: 2 3, on right: 1 3 20
declaration (36)
on left: 4 5 6, on right: 2 3
variable_dec (37)
on left: 7 8, on right: 5 14 15
assignment (38)
on left: 9, on right: 8 23
var_list (39)
on left: 10 11 12, on right: 11 22
function_dec (40)
on left: 13, on right: 4
p_list (41)
on left: 14 15, on right: 13 15
type (42)
on left: 16 17 18 19, on right: 7 8 13
scope (43)
on left: 20 21, on right: 13
function_call (44)
on left: 22, on right: 24
expression (45)
on left: 23 24 25 26 27 28, on right: 6 9 10 11 25 26 27
constant (46)
on left: 29 30, on right: 26 27 28
identifier (47)
on left: 31, on right: 7 9 13 22 29
num (48)
on left: 32 33, on right: 30
arithmetic_op (49)
on left: 34 35 36 37, on right: 26
logical_op (50)
on left: 38 39 40 41 42 43, on right: 27
state 18
26 expression: constant . arithmetic_op expression
27 | constant . logical_op expression
28 | constant . [$end, TCPA, TCB, TCOMMA, TSEMIC, TINT, TFLOAT, TD, TCHAR, TINTEGER, TDOUBLE, TID, TOPA]
34 arithmetic_op: . TPLUS
35 | . TMINUS
36 | . TDIV
37 | . TMULT
38 logical_op: . TLT
39 | . TGT
40 | . TAND
41 | . TOR
42 | . TEQUAL
43 | . TNE
TPLUS shift, and go to state 26
TMINUS shift, and go to state 27
TDIV shift, and go to state 28
TMULT shift, and go to state 29
TLT shift, and go to state 30
TGT shift, and go to state 31
TAND shift, and go to state 32
TOR shift, and go to state 33
TEQUAL shift, and go to state 34
TNE shift, and go to state 35
$default reduce using rule 28 (expression)
arithmetic_op go to state 36
logical_op go to state 37
state 19
9 assignment: identifier . TASSIGN expression
22 function_call: identifier . TOPA var_list TCPA TSEMIC
29 constant: identifier . [$end, TCPA, TCB, TCOMMA, TSEMIC, TINT, TFLOAT, TD, TCHAR, TPLUS, TMINUS, TDIV, TMULT, TLT, TGT, TAND, TOR, TEQUAL, TNE, TINTEGER, TDOUBLE, TID, TOPA]
TASSIGN shift, and go to state 38
TOPA shift, and go to state 39
TOPA [reduce using rule 29 (constant)]
$default reduce using rule 29 (constant)
state 20
30 constant: num .
$default reduce using rule 30 (constant)
答案 0 :(得分：1)
根据野牛的输出，从州19开始，可以在（）的前瞻中减少expression。这怎么可能呢？换句话说，在什么情况下可以expression之后是一个左括号？
通过语法搜索仅显示TOPA的三种用法。其中两个（函数声明和函数调用）跟在identifier之后，identifier无法导出expression，所以它必须是第三个：
expression: TOPA expression TCPA;
但是，在的实例之前立即减少expression的唯一方法是（，如果两个expression可能连续发生的话。 ，在C语言中，通过要求; 来分隔语句（可能是，以expression开头，或以command_list: declaration
| command_list declaration
declaration: expression
结束）消除了可能性，我想这是你的意图。
然而，我们看到：
'('允许两个连续的表达式而不插入分号。
与往常一样，我鼓励在野牛语法中使用更具可读性的标记。 TOPA比COB更容易理解，我真的不知道{{1}}可能是什么。但这是一个风格问题。