我有以下Bison语法：
%error-verbose
%{
#include "node.h"
NBlock *programBlock;
#define YYDEBUG 1
extern int yylex();
void yyerror(const char *s) { printf("Error: %s\n", s); }
%}
%union {
Node *node;
NBlock *block;
NBody *body;
NHeader *header;
NExpression *expression;
NStatement *statement;
NIdentifier *identifier;
NVariableDeclaration *variableDeclaration;
NDoWhileStatement *doWhileStatement;
NWhileStatement *whileStatement;
NIfStatement *ifStatement;
NForStatement *forStatement;
std::vector<NVariableDeclaration*> *variableDeclarations;
std::vector<NExpression*> *expressions;
std::vector<NStatement*> *statements;
std:string *string;
int token;
}
/*
The %token directive is used to associate a type to a terminal symbol.
%token <type> 'terminal_list'
associates the specific type <type> to each terminal in 'terminal_list'.
The type <type> is the same used in the %union declaration
*/
%token <string> TIDENTIFIER TINTEGER TDOUBLE
%token <token> TCEQ TCNE TCLT TCLE TCGT TCGE TEQUAL
%token <token> TLPAREN TRPAREN TLBRACE TRBRACE TCOMMA TDOT
%token <token> TPLUS TMINUS TMUL TDIV TDO TDOUBLE_TYPE TINT_TYPE
%token <token> TELSE TFOR TIF TSEMICOLON TTHEN TWHILE
/*
The %type directive is used to associate a type to a nonterminal symbol.
%type <type> nonterminal_list
associates the specific type <type> to each nonterminal in 'nonterminal_list'.
The type <type> is the same used in the %union declaration
*/
%type <expression> expression term factor
%type <block> program body header tail statements
%type <statement> statement forStatement ifStatement doWhileStatement whileStatement variableDeclaration
%type <token> comparison
%type <string> identifier_type
/*
Operator precedence for mathematical operators
*/
%left TPLUS TMINUS
%left TMUL TDIV
%left TCEQ TCNE TCLT TCLE TCGT TCGE
/*
Start grammar symbol
*/
%start program
%%
program: TLBRACE body TRBRACE { printf("Reduce body to program\n"); }
;
body: header TLBRACE block TRBRACE tail { printf("Reduce header block tail to body\n"); }
;
header: TLBRACE variableDeclarations TRBRACE { printf("Reduce variableDeclarations to header\n"); }
| TLBRACE TRBRACE { printf("Reduce empty to header\n"); }
;
variableDeclarations: variableDeclaration TSEMICOLON { printf("Reduce variable declaration to header\n"); }
| variableDeclarations variableDeclaration TSEMICOLON { printf("Reduce variable declaration list to header\n"); }
;
tail: TLBRACE statements TRBRACE { printf("reduce statement list to tail\n"); }
| TLBRACE TRBRACE { printf("Reduce empty to tal\n"); }
;
statements: statement TSEMICOLON { printf("Reduce statement to statement list\n"); }
| statements statement TSEMICOLON { printf("Reduce statement list to statement list\n"); }
;
statement: ifStatement { printf("Reduce if to statement\n"); };
| forStatement { printf("Reduce for to statement\n"); };
| doWhileStatement { printf("Reduce doWhile to statement\n"); };
| whileStatement { printf("reduce while to statement\n"); }
| TIDENTIFIER TEQUAL expression { printf("Reduce assignment to expression\n"); }
;
forStatement: TFOR TLPAREN expression TSEMICOLON expression TSEMICOLON expression TRPAREN block { printf("Reduce for to for statement\n"); }
;
ifStatement: TIF expression TTHEN block { printf("Reduce if to if statement\n"); }
| TIF expression block TELSE block { printf("Reduce ifelse to if statement\n"); }
;
doWhileStatement: TDO block TWHILE expression { printf("reduce dowhile to while statement\n"); }
;
whileStatement: TWHILE block expression { printf("Reduce while to while statement\n"); }
;
block: TLBRACE statements TRBRACE { printf("Reduce statement list to block\n"); }
| TLBRACE TRBRACE { printf("Reduce empty to block\n"); }
;
variableDeclaration: identifier_type TIDENTIFIER { printf("reduce uninitialized identifier to variable declaration\n"); }
| identifier_type TIDENTIFIER TEQUAL expression { printf("Reduce initialized identifier to variable declaration\n"); }
;
identifier_type: TINT_TYPE { printf("Reduce int to identifier type\n"); }
| TDOUBLE_TYPE { printf("Reduce double to identifier type\n"); }
| { printf("Reduce empty to identifier type\n"); }
;
expression: term { printf("Reduce term to expresson\n"); }
| expression comparison expression { printf("Reduce comparison to expression\n"); }
| expression TPLUS term { printf("Reduce addition to expression\n"); }
| expression TMINUS term { printf("Reduce subtraction to expression\n"); }
;
term: factor { printf("Reduce factor to term\n"); }
| term TMUL factor { printf("Reduce multiplication to term\n"); }
| term TDIV factor { printf("Reduce division to term\n"); }
;
factor: TLPAREN expression TRPAREN { printf("Reduce nested expression to expression\n"); }
| TMINUS factor { printf("Reduce -factor to factor\n"); }
| TIDENTIFIER { printf("Reduce identifier to factor\n"); }
| TINTEGER { printf("Reduce integer to numeric\n"); }
| TDOUBLE { printf("Reduce double to numeric\n"); }
;
comparison: TCEQ { printf("Reduce eq to comparison\n"); }
| TCNE { printf("Reduce ne to comparison\n"); }
| TCLT { printf("Reduce lt to comparison\n"); }
| TCLE { printf("Reduce le to comparison\n"); }
| TCGT { printf("reduce gt to comparison\n"); }
| TCGE { printf("Reduce ge to comparison\n"); }
;
我得到8次转移/减少冲突，我不知道如何修复。
以下是我使用--report = all参数生成的parser.output文件的piace。这是受8个转变/减少冲突影响的状态：
State 79
29 expression: expression . comparison expression
29 | expression comparison expression . [TCEQ, TCNE, TCLT, TCLE, TCGT, TCGE, TRPAREN, TLBRACE, TPLUS, TMINUS, TSEMICOLON, TTHEN]
30 | expression . TPLUS term
31 | expression . TMINUS term
40 comparison: . TCEQ
41 | . TCNE
42 | . TCLT
43 | . TCLE
44 | . TCGT
45 | . TCGE
TCEQ shift and go to state 56
TCNE shift and go to state 57
TCLT shift and go to state 58
TCLE shift and go to state 59
TCGT shift and go to state 60
TCGE shift and go to state 61
TPLUS shift and go to state 62
TMINUS shift and go to state 63
TCEQ [reduction with rule 29 (expression)]
TCNE [reduction with rule 29 (expression)]
TCLT [reduction with rule 29 (expression)]
TCLE [reduction with rule 29 (expression)]
TCGT [reduction with rule 29 (expression)]
TCGE [reduction with rule 29 (expression)]
TPLUS [reduction with rule 29 (expression)]
TMINUS [reduction with rule 29 (expression)]
$default reduction with rule 29 (expression)
comparison go to state 64
如果我理解的话，问题是解析器不知道是继续读取另一个文本还是立即减少规则表达式：表达式比较表达式。
我想说立即减少是正确的。但如果我这是正确的，那么我如何强制立即减少转移？
答案 0 :(得分：5)
您的语法含糊不清 - 像1 < 2 < 3这样的输入可以解析为(1 < 2) < 3或1 < (2 < 3)。
有两种方法可以解决这个问题 - 添加%left / %right / %nonassoc指令以使用bison的内部优先级处理，或引入其他级别的规则来处理它。
现在，您的其他运营商（* / + -）您正在做这些 - 这通常是一个错误，您想要做的只是非此即彼。但是如果你做两者都做，那么附加规则将优先，优先级指令将被忽略，有时会引起令人惊讶的问题。
这样的关系的“正常”处理就是说你不能有多个（1 < 2 < 3是一个语法错误，不应该左右递归解析。）另外做这个规则，您将表达式规则更改为：
expression: add_expression
| add_expression comparison add_expression
;
add_expression: term
| add_expression TPLUS term
| add_expression TMINUS term
;
使用优先级指令，摆脱term，factor和comparison（将它们全部移到expression并添加：
%nonassoc TCEQ TCNE TCLT TCLE TCGT TCGE
%left TPLUS TMINUS
%left TMUL TDIV
答案 1 :(得分：1)
问题在于关联规则（如您的%left指令）不能通过语法间接工作。如果您取消comparison规则并将所有比较运算符拉入expression规则，则问题就会消失。 （我用Bison v2.4.1验证了这一点。）
这可能不方便，因为它使expression比你更加冗长。解决方法是将决策推回扫描程序。将COMPARISON定义为单个标记，并将比较的风格作为单独的枚举类型传递到yylval，以便$n可用。
答案 2 :(得分：0)
感谢您的回答。这是完整的Bison语法：
%error-verbose
%{
#include "node.h"
#include <iostream>
#include <string>
NBlock *programBlock;
#define YYDEBUG 1
extern int yylex();
void yyerror(const char *) { printf("Error: %s\n", s); }
%}
%union {
Node *node;
NBlock *block;
NBody *body;
NHeader *header;
NExpression *expression;
NStatement *statement;
NIdentifier *identifier;
NVariableDeclaration *variableDeclaration;
NDoWhileStatement *doWhileStatement;
NWhileStatement *whileStatement;
NIfStatement *ifStatement;
NForStatement *forStatement;
std::vector<NVariableDeclaration*> *variableDeclarations;
std::vector<NExpression*> *expressions;
std::vector<NStatement*> *statements;
std:string *string;
int token;
}
%token <string> TIDENTIFIER TINTEGER TDOUBLE
%token <token> TCEQ TCNE TCLT TCLE TCGT TCGE TEQUAL
%token <token> TLPAREN TRPAREN TLBRACE TRBRACE TCOMMA TDOT
%token <token> TPLUS TMINUS TMUL TDIV TDO TDOUBLE_TYPE TINT_TYPE
%token <token> TELSE TFOR TIF TSEMICOLON TTHEN TWHILE TLSQUARE TRSQUARE
%type <expression> expression term factor
%type <block> program body header tail
%type <statements> statements
%type <statement> statement
%type <forStatement> forStatement
%type <ifStatement> ifStatement
%type <doWhileStatement> doWhileStatement
%type <whileStatement> whileStatement
%type <variableDeclaration> variableDeclaration
%type <token> comparison
%type <string> identifier_type
%type <variableDeclarations> variableDeclarations
/*
Start grammar symbol
*/
%start program
%%
program: TLBRACE body TRBRACE { printf("Reduce body to program\n"); }
;
body: header TLBRACE block TRBRACE tail { printf("Reduce header block tail to body\n"); }
;
header: TLBRACE variableDeclarations TRBRACE { printf("Reduce variableDeclarations to header\n"); }
| TLBRACE TRBRACE { printf("Reduce empty to header\n"); }
;
variableDeclarations: variableDeclaration TSEMICOLON { printf("Reduce variable declaration to header\n"); }
| variableDeclarations variableDeclaration TSEMICOLON { printf("Reduce variable declaration list to header\n"); }
;
tail: TLBRACE statements TRBRACE { printf("reduce statement list to tail\n"); }
| TLBRACE TRBRACE { printf("Reduce empty to tal\n"); }
;
statements: statement TSEMICOLON { printf("Reduce statement to statement list\n"); }
| statements statement TSEMICOLON { printf("Reduce statement list to statement list\n"); }
;
statement: ifStatement { printf("Reduce if to statement\n"); };
| forStatement { printf("Reduce for to statement\n"); };
| doWhileStatement { printf("Reduce doWhile to statement\n"); };
| whileStatement { printf("reduce while to statement\n"); }
| TIDENTIFIER TEQUAL expression { printf("Reduce assignment to expression\n"); }
| TIDENTIFIER TLSQUARE TINTEGER TRSQUARE TEQUAL expression { printf("Reduce array assignment to expression\n"); }
;
forStatement: TFOR TLPAREN expression TSEMICOLON expression TSEMICOLON expression TRPAREN block { printf("Reduce for to for statement\n"); }
;
ifStatement: TIF expression TTHEN block { printf("Reduce if to if statement\n"); }
| TIF expression TTHEN block TELSE block { printf("Reduce ifelse to if statement\n"); }
;
doWhileStatement: TDO block TWHILE expression { printf("reduce dowhile to while statement\n"); }
;
whileStatement: TWHILE block expression { printf("Reduce while to while statement\n"); }
;
block: TLBRACE statements TRBRACE { printf("Reduce statement list to block\n"); }
| TLBRACE TRBRACE { printf("Reduce empty to block\n"); }
;
variableDeclaration: identifier_type TIDENTIFIER { printf("Reduce uninitialized identifier to variable declaration\n"); }
| identifier_type TIDENTIFIER TLSQUARE TINTEGER TRSQUARE { printf("Reduce array to variable declaration\n"); }
| identifier_type TIDENTIFIER TEQUAL expression { printf("Reduce initialized identifier to variable declaration\n"); }
| identifier_type TIDENTIFIER TLSQUARE TINTEGER TRSQUARE TEQUAL expression { printf("Reduce initialized array to variable declaration\n"); }
;
identifier_type: TINT_TYPE { printf("Reduce int to identifier type\n"); }
| TDOUBLE_TYPE { printf("Reduce double to identifier type\n"); }
| { printf("Reduce empty to identifier type\n"); }
;
expression: add-expression { printf("Reduce add-expression to expression\n"); }
|add-expression comparison add-expression { printf("Reduce add-expression comparison add-expression to expression\n"); }
add-expression: term { printf("Reduce term to expresson\n"); }
| add-expression TPLUS term { printf("Reduce addition to expression\n"); }
| add-expression TMINUS term { printf("Reduce subtraction to expression\n"); }
;
term: factor { printf("Reduce factor to term\n"); }
| term TMUL factor { printf("Reduce multiplication to term\n"); }
| term TDIV factor { printf("Reduce division to term\n"); }
;
factor: TLPAREN expression TRPAREN { printf("Reduce nested expression to expression\n"); }
| TMINUS factor { printf("Reduce -factor to factor\n"); }
| TIDENTIFIER { printf("Reduce identifier to factor\n"); }
| TINTEGER { printf("Reduce integer to numeric\n"); }
| TDOUBLE { printf("Reduce double to numeric\n"); }
;
comparison: TCEQ { printf("Reduce eq to comparison\n"); }
| TCNE { printf("Reduce ne to comparison\n"); }
| TCLT { printf("Reduce lt to comparison\n"); }
| TCLE { printf("Reduce le to comparison\n"); }
| TCGT { printf("reduce gt to comparison\n"); }
| TCGE { printf("Reduce ge to comparison\n"); }
;