Antlr4解析器中缺少变量

Question

I am trying to build a symbol table for a language using Antlr4. I have the following rule in my grammar file.

/* Global String Declaration */
//string_decl       : STRING id ASSIGN str SEMICOLON ;
string_decl returns [StrEntry s] : STRING id ASSIGN ex=str SEMICOLON 
           { $s = new StrEntry(); s.addID($id.text); s.addValue($ex.text);} ;

I also created a StrEntry class (a dummy implementation)

public class StrEntry{


    String value;
    String id;
    String type;


    void addID(String x){
        id = x;
    }

    void addValue(String c){
        value = c;
    }

}

When I compile ( javac *.java ) I get the following error:

MicroParser.java:382: error: cannot find symbol
                         ((String_declContext)_localctx).s =  new   StrEntry(); s.addID((((String_declContext)_localctx).id!=null?  _input.getText(((String_declContext)_localctx).id.start,    ((String_declContext)_localctx).id.stop):null));    s.addValue((((String_declContext)_localctx).ex!=null?_input.getText(((String_declContext)_localctx).ex.start,   ((String_declContext)_localctx).ex.stop):null));
                                                                                                                                                                                                                                        ^
  symbol:   variable s
  location: class MicroParser

It says variable s of type StrEntry is missing, but I have defined it in my grammar file. I don't think editing it in MicroParser.java file is a good idea as it was generated by Antlr4.

What should I do?

Answer 1

$s = new StrEntry(); s.addID($id.text); s.addValue($ex.text)

Here you're using both $s (which will be translated to _localctx.s in the generated Java code) and s (which will remain just s ). The latter is the symbol that the compiler can't find because there is no variable with that name defined in that block.

In other words, you just need to consistently use $s instead of s and it will work fine.