Question

我正在使用Jison开发一种语言，而我遇到的一个问题是运算符优先级。我希望比较运算符成为第一个要评估的运算符，例如，1 + 2 < 3 - 3 * 4将成为(1+2) < (3 - (3 * 4))

我现在的规则：

expression
  : expression OP_COMPARISON expression
    { $$ = { type: "Comparison", operator: $2, args: [$1, $3], location: locationFromObject(@$) } }
  | literal
    { $$ = $literal; }
  | NAME
    { $$ = { type: "Variable", variable: $1, location: locationFromObject(@$) }; }
  | field
    { $$ = { type: "Field", field: $field, location: locationFromObject(@$) }; }
  | '(' ':' typename ')' expression
    { $$ = { type: "Cast", cast_type: $typename, expression: $expression, location: locationFromObject(@$) }; }
  | function_call
    { $$ = $function_call; $$.type = "FunctionCall"; }
  | method_call
    { $$ = $method_call; $$.type = "FunctionCall"; }
  | '(' expression ')'
    { $$ = { type: "Grouped", expression: $expression, location: locationFromObject(@$) }; }
  | OP_PREPOSTFIX expression
    { $$ = { type: "Prefix", operator: $1, arg: $expression, location: locationFromObject(@$) }; }
  | expression OP_PREPOSTFIX
      { $$ = { type: "Postfix", operator: $2, arg: $expression, location: locationFromObject(@$) }; }
  | expression OP_ARITHMETIC expression
    {
      if($1.type == "Arithmetic"){
        $$ = $1;
        $$.args.push($3);
        $$.operators.push($2);
        $$.location = locationFromObject(@$);
      }else{
        $$ = { type: "Arithmetic", operators: [$2], args: [$1, $3], location: locationFromObject(@$) };
      }
    }
  | expression OP_LOGICAL expression
    {
      if($1.type == "Logical"){
        $$ = $1;
        $$.args.push($3);
        $$.operators.push($2);
        $$.location = locationFromObject(@$);
      }else{
        $$ = { type: "Logical", operators: [$2], args: [$1, $3], location: locationFromObject(@$) };
      }
    }
  | '!' expression
    { $$ = {type: "LogicalNot", arg: $expression, location: locationFromObject(@$) }; }
  ;

任何帮助都将不胜感激

Answer 1

将运算符优先级转换为无上下文语法的最佳方法是使用几个指示优先级的规则。例如，使用简单的算术：

expression : expression PLUS term
           | expression MINUS term
           | term
           ;

term : term MULTIPLY factor
     | term DIVIDE factor
     | factor
     ;

factor : IDENTIFIER
       | CONSTANT
       | LEFT expression RIGHT
       ;

使用此层次结构实现 BODMAS 算术规则。

你可以用你的语法做类似的事情：分成几个代表不同优先层的规则。

（有关详细信息，请参阅编写计算机科学文本的标准编译器）

Jison运算符优先级

1 个答案: