Question

I am working on ANLTR to support type checking. I am in trouble at some point. I will try to explain it with an example grammar, suppose that I have the following:

@members {
    private java.util.HashMap<String, String> mapping = new java.util.HashMap<String, String>();
}

var_dec  
    : type_specifiers d=dec_list? SEMICOLON 
    {
         mapping.put($d.ids.get(0).toString(), $type_specifiers.type_name);
         System.out.println("identext = " + $d.ids.get(0).toString() + " - " + $type_specifiers.type_name);
    };

type_specifiers returns [String type_name]
    : 'int' { $type_name = "int";}
    | 'float' {$type_name = "float"; }
    ;

dec_list returns [List ids]
    : ( a += ID brackets*) (COMMA ( a += ID brackets* ) )* 
    {$ids = $a;}
    ; 

brackets : LBRACKET (ICONST | ID) RBRACKET;

ID : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*;
LBRACKET : '[';  
RBRACKET : ']';

In rule dec_list, you will see that I am returning List with ids. However, in var_dec when I try to put the first element of the list (I am using only get(0) just to see the return value from dec_list rule, I can iterate it later, that’s not my point) into mapping I get a whole string like

[@4,6:6='a',<17>,1:6] 

for an input

int   a, b;

What I am trying to do is to get text of each ID, in this case a and b in the list of index 0 and 1, respectively.

Does anyone have any idea?

Answer 1

The += operator creates a List of Tokens, not just the text these Tokens match. You’ll need to initialize the List in the @init{...} block of the rule and add the inner-text of the tokens yourself.

Also, you don’t need to do this:

type_specifiers returns [String type_name]
  :  'int' { $type_name = "int";}
  |  ...
  ;

simply access type_specifiers‘s text attribute from the rule you use it in and remove the returns statement, like this:

var_dec
  :  t=type_specifiers ... {System.out.println($t.text);}
  ;

type_specifiers
  :  'int'
  |  ...
  ;

Try something like this:

grammar T;

var_dec  
  :  type dec_list? ';' 
     {
       System.out.println("type = " + $type.text);
       System.out.println("ids  = " + $dec_list.ids);
     }
  ;

type
  :  Int
  |  Float
  ;

dec_list returns [List ids]
@init{$ids = new ArrayList();}
  :  a=ID {$ids.add($a.text);} (',' b=ID {$ids.add($b.text);})*
  ;

Int   : 'int';
Float : 'float';
ID    : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*;
Space : ' ' {skip();};

which will print the following to the console:

type = int
ids  = [a, b, foo]

If you run the following class:

import org.antlr.runtime.*;

public class Main {
  public static void main(String[] args) throws Exception {
    TLexer lexer = new TLexer(new ANTLRStringStream("int a, b, foo;"));
    TParser parser = new TParser(new CommonTokenStream(lexer));
    parser.var_dec();
  }
}