如何在我的语法中执行操作优先级 (+ * -/)? [英] How to do Priority of Operations (+ * - /) in my grammars?

问题描述

我使用 antlr 4 定义了我自己的语法，我想根据操作的优先级 (+ * -/) ....

I define my own grammars using antlr 4 and I want to build tree true According to Priority of Operations (+ * - /) ....

我在 do Priority of Operations (* +) 上找到示例，它工作正常......

I find sample on do Priority of Operations (* +) it work fine ...

我尝试编辑它以添加操作优先级 (-/) 但我失败了 :(

I try to edit it to add the Priority of Operations (- /) but I failed :(

操作优先级 (+ *) 的语法是:

the grammars for Priority of Operations (+ *) is :

 println:PRINTLN  expression SEMICOLON {System.out.println($expression.value);};
 expression returns [Object value]:
  t1=factor {$value=(int)$t1.value;}
  (PLUS t2=factor{$value=(int)$value+(int)$t2.value;})*;

  factor returns [Object value]: t1=term {$value=(int)$t1.value;}
  (MULT t2=term{$value=(int)$value*(int)$t2.value;})*;

 term returns [Object value]:
  NUMBER {$value=Integer.parseInt($NUMBER.text);}
   | ID {$value=symbolTable.get($value=$ID.text);}
   | PAR_OPEN expression {$value=$expression.value;} PAR_CLOSE
   ;
MULT :'*';
PLUS :'+';

MINUS:'-';
DIV:'/' ; 

如何向它们添加操作优先级 (-/) ?

How I can add to them the Priority of Operations (- /) ?

推荐答案

在 ANTLR3(和 ANTLR4)中 * 和 / 可以被赋予比 更高的优先级+ 和 - 像这样:

In ANTLR3 (and ANTLR4) * and / can be given a higher precedence than + and - like this:

println
 : PRINTLN  expression SEMICOLON
 ;

expression
 : factor ( PLUS factor 
          | MINUS factor
          )*
 ;

factor
 : term ( MULT term
        | DIV term
        )*
 ;

term
 : NUMBER
 | ID
 | PAR_OPEN expression PAR_CLOSE
 ;

但在 ANTLR4 中，这也适用:

But in ANTLR4, this will also work:

println
 : PRINTLN  expression SEMICOLON
 ;

expression
 : NUMBER
 | ID
 | PAR_OPEN expression PAR_CLOSE
 | expression ( MULT | DIV ) expression   // higher precedence
 | expression ( PLUS | MINUS ) expression // lower precedence
 ;

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