Beaver解析器生成器移位-减少与悬挂其他冲突有关的冲突

Question

我将向Beaver解析器生成器提供(生成的)语法。多重移位-减少冲突是由以下规则中的其他问题引起的：

Condition
    = IF LPAR Expression.expression RPAR Statement.trueStatement OptionalStatement_1.elem2  
    ;
OptionalStatement_1
    = ELSE StatementArray3.falseStatement   
    |   
    ;

我认为悬挂的其他问题不会是一个问题，因为工具默认选择SHIFT，这是对悬空的其他问题AFAIK的一个公认的解决方案。但是，有一些问题，因为我还有16条警告，我不明白为什么：

grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (ELSE: SHIFT; goto 93) over (ELSE: REDUCE OptionalStatement_1 = ) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (LBR: SHIFT; goto 5) over (LBR: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (IF: SHIFT; goto 18) over (IF: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (RETURN: SHIFT; goto 95) over (RETURN: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (DO: SHIFT; goto 100) over (DO: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (READ: SHIFT; goto 107) over (READ: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (WRITE: SHIFT; goto 110) over (WRITE: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (SEMICOLON: SHIFT; goto 113) over (SEMICOLON: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (WHILE: SHIFT; goto 114) over (WHILE: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (LPAR: SHIFT; goto 63) over (LPAR: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (PLUSPLUS: SHIFT; goto 71) over (PLUSPLUS: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (PLUS: SHIFT; goto 73) over (PLUS: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (EXCL: SHIFT; goto 75) over (EXCL: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (MINUS: SHIFT; goto 77) over (MINUS: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (MINUSMINUS: SHIFT; goto 79) over (MINUSMINUS: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (VALUE: SHIFT; goto 81) over (VALUE: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.
grammar.grammar: Warning: Resolved Shift-Reduce conflict by selecting (IDENT: SHIFT; goto 82) over (IDENT: REDUCE OptionalStatement_1 = ELSE StatementArray3.falseStatement) using precedence.

结果是，在StatementArray3中，有垃圾被注入其他分支(完全错误的类型，一个列表而不是可选的，充斥着以下语句中的大量内容)。能不能请人解释一下这些转移是什么--减少冲突(除了明显的第一个)？头脑，语法是由类模型生成的，所以对于这个问题非常具体的解决方案不是最好的，我需要一般地解决这类问题，或者改变语法。

由另一种方法生成的以前的语法(我想避免)产生了以下语法：

Condition
    = IF LPAR Expression.expression RPAR Statement.trueStatement    
    | IF LPAR Expression.expression RPAR Statement.trueStatement ELSE Statement.falseStatement  
    ;

但是，对于以下输入，在编译过程中不会发生冲突：

{
  if(b == 21)
    c = 10;
  else
    c = 15;
}

解析器在运行时失败，只需跳过其他任务并将第二个赋值作为顶级任务处理：

4,4-4,7: Syntax Error: unexpected token "else"
4,4-4,7: Recovered: removed unexpected token "else"

完整的有问题的语法(除去%import、%typeof of和{: ... :})：

%terminals PERC, ASSIGNDIV, LT, RPAR, VALUE, DO, ASSIGN, PLUSPLUS, QUESTION, MINUS, WRITE, RETURN, LPAR, SEMICOLON, ASSIGNADD, ELSE, LBR, IF, COMMA, RBR, OR, SLASH, MINUSMINUS, COLON, EQ, GT, READ, ASSIGNMUL, STAR, IDENT, ASSIGNSUB, ASSIGNMOD, AND, GTE, WHILE, NEQ, EXCL, LTE, PLUS;

%left LPAR, RPAR;
%nonassoc PLUSPLUS, MINUSMINUS;
%left PREC_13_1, EXCL, PREC_13_2;
%left PERC, SLASH, STAR;
%left PLUS, MINUS;
%left LT, LTE, GT, GTE;
%left NEQ, EQ;
%left AND;
%left OR;
%left QUESTION, COLON;
%right ASSIGN, ASSIGNADD, ASSIGNMUL, ASSIGNDIV, ASSIGNSUB, ASSIGNMOD;


%goal Program;

Number
    = VALUE.value   
    ;

Program
    = FunctionArray1.functions Block.main   
    ;

UnaryOperation
    = PLUSPLUS Expression.expression    
    | PLUS Expression.expression @ PREC_13_1    
    | EXCL Expression.expression    
    | MINUS Expression.expression @ PREC_13_2   
    | MINUSMINUS Expression.expression  
    ;

Block
    = LBR StatementArray3.statements RBR    
    ;

BinaryOperation
    = Expression.expression1 NEQ Expression.expression2 
    | Expression.expression1 OR Expression.expression2  
    | Expression.expression1 PERC Expression.expression2    
    | Expression.expression1 EQ Expression.expression2  
    | Expression.expression1 PLUS Expression.expression2    
    | Expression.expression1 LT Expression.expression2  
    | Expression.expression1 MINUS Expression.expression2   
    | Expression.expression1 LTE Expression.expression2 
    | Expression.expression1 SLASH Expression.expression2   
    | Expression.expression1 GT Expression.expression2  
    | Expression.expression1 ASSIGN Expression.expression2  
    | Expression.expression1 STAR Expression.expression2    
    | AssignmentGeneric.val 
    | Expression.expression1 GTE Expression.expression2 
    | Expression.expression1 AND Expression.expression2 
    ;

Expression
    = LPAR Expression.val RPAR  
    | Expression.expression1 QUESTION Expression.expression2 COLON Expression.expression3   
    | UnaryOperation.val    
    | Number.val    
    | Variable.val  
    | FunctionCall.val  
    | BinaryOperation.val   
    ;

ParameterArray2
    = ParameterArray2.list COMMA Parameter.elem 
    |   
    | Parameter.elem    
    ;

Statement
    = Block.val 
    | Condition.val 
    | ReturnFunction.val    
    | ExpressionStatement.val   
    | DoWhile.val   
    | Read.val  
    | Write.val 
    | EmptyStatement.val    
    | WhileStatement.val    
    ;

Parameter
    = IDENT.ident   
    ;

Write
    = WRITE Expression.expression SEMICOLON 
    ;

OptionalStatement_1
    = ELSE StatementArray3.falseStatement   
    |   
    ;

FunctionArray1
    = FunctionArray1.list Function.elem 
    |   
    ;

WhileStatement
    = WHILE LPAR Expression.expression RPAR Statement.statement 
    ;

ExpressionArray4
    = ExpressionArray4.list COMMA Expression.elem   
    |   
    | Expression.elem   
    ;

ExpressionStatement
    = Expression.expression SEMICOLON   
    ;

Variable
    = IDENT.ident   
    ;

EmptyStatement
    = SEMICOLON 
    ;

Read
    = READ IDENT.ident SEMICOLON    
    ;

FunctionCall
    = IDENT.ident LPAR ExpressionArray4.expressions RPAR    
    ;

Condition
    = IF LPAR Expression.expression RPAR Statement.trueStatement OptionalStatement_1.elem2  
    ;

DoWhile
    = DO Statement.statement WHILE LPAR Expression.expression RPAR SEMICOLON    
    ;

Function
    = IDENT.ident LPAR ParameterArray2.parameters RPAR Block.body   
    ;

ReturnFunction
    = RETURN Expression.expression SEMICOLON    
    ;

StatementArray3
    = StatementArray3.list Statement.elem   
    |   
    ;

AssignmentGeneric
    = Expression.expression1 ASSIGNADD Expression.expression2   
    | Expression.expression1 ASSIGNMUL Expression.expression2   
    | Expression.expression1 ASSIGNDIV Expression.expression2   
    | Expression.expression1 ASSIGNSUB Expression.expression2   
    | Expression.expression1 ASSIGNMOD Expression.expression2   
    ;

Answer 1

语法生成中存在一个问题。它应该是

OptionalStatement_1
    = ELSE Statement.falseStatement   
    |   
    ;

不是StatementArray3.falseStatement

在正确生成ELSE Statement.falseStatement替代方案之后，只会出现一个SHIFT -还原冲突，而我可以依赖默认的SHIFT操作。