[antlr-interest] Own Tree Class

[Bart Kiers]

On Mon, Feb 14, 2011 at 6:50 PM, Filip Habr <habr.filip at seznam.cz> wrote:

> Hello, can you help me somebody? I wrote ExpressionParser in ANTLR, which
> parse
> math expression to a tree. I was using CommonTree class as a target. Now I
> need
> to create my own tree class, because I have to create additional methods.
> Is
> there any way to create own tree class, which could be used by ANTLR
> grammar as
> a target tree class.
>
> options {
>        language=CSharp2;
>        output=AST;
>        ASTLabelType=MY_OWN_CLASS;
>        }
>
> Best help for me would be an advice, how to write class like CommonTree,
> because
> the code of CommonTree methods is not visible of course. Every class, i
> have
> written doesn't work. Thanks a lot!!!!




On Mon, Feb 14, 2011 at 6:50 PM, Filip Habr <habr.filip at seznam.cz> wrote:

> Hello, can you help me somebody? I wrote ExpressionParser in ANTLR, which
> parse
> math expression to a tree. I was using CommonTree class as a target. Now I
> need
> to create my own tree class, because I have to create additional methods.
> Is
> there any way to create own tree class, which could be used by ANTLR
> grammar as
> a target tree class.
>
> options {
>        language=CSharp2;
>        output=AST;
>        ASTLabelType=MY_OWN_CLASS;
>        }
>
> Best help for me would be an advice, how to write class like CommonTree,
> because
> the code of CommonTree methods is not visible of course. Every class, i
> have
> written doesn't work. Thanks a lot!!!!
>
>

Besides writing your own CommonTree subclass and adding `` to your
`options{...}` section, you should write your own CommonTreeAdaptor that
actually creates instances of your custom tree(s).

A little demo. Specifically note the lines that have `// !!!` after them:

// file://BooleExp.g
grammar BoolExp;

options {
  output=AST;
  ASTLabelType=BoolExpTree;               // !!!
}

parse
  :  exp EOF -> exp
  ;

exp
  :  orExp
  ;

orExp
  :  andExp (Or^ andExp)*
  ;

andExp
  :  atom (And^ atom)*
  ;

atom
  :  '(' exp ')' -> exp
  |  True
  |  False
  ;

Or    : 'OR' | '||';
And   : 'AND' | '&&';
True  : 'true';
False : 'false';
Space : (' ' | '\t' | '\r' | '\n') {$channel=HIDDEN;};

// file://Main.java
import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;

public class Main {

    private static void walk(BoolExpTree tree, int depth) {
        if(tree == null) {
            return;
        }
        for(int i = 0; i < depth; i++) {
            System.out.print(". ");
        }
        System.out.println(tree);
        walk(tree.left(), depth + 1);
        walk(tree.right(), depth + 1);
    }

    public static void main(String[] args) throws Exception {
        ANTLRStringStream in = new ANTLRStringStream("true AND (false ||
true && (true OR false))");
        BoolExpLexer lexer = new BoolExpLexer(in);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        BoolExpParser parser = new BoolExpParser(tokens);
        parser.setTreeAdaptor(new BoolExpTreeAdaptor());
      // !!!
        BoolExpParser.parse_return returnValue = parser.parse();
        CommonTree tree = (BoolExpTree)returnValue.getTree();
        walk((BoolExpTree)tree, 0);
    }
}

class BoolExpTree extends CommonTree {

    public BoolExpTree(Token token) {
        super(token);
    }

    public BoolExpTree left() {
        return super.getChildCount() > 0 ? (BoolExpTree)super.getChild(0) :
null;
    }

    public BoolExpTree right() {
        return super.getChildCount() > 1 ? (BoolExpTree)super.getChild(1) :
null;
    }

    @Override
    public String toString() {
        return "BoolExpTree[" + super.toString() + "]";
    }
}

class BoolExpTreeAdaptor extends CommonTreeAdaptor {

    @Override
    public Object create(Token token) {
        return new BoolExpTree(token);
    }
}


When generating a lexer/parser, compiling all .java source files, and
running the main class:

java -cp antlr-3.2.jar org.antlr.Tool BoolExp.g
javac -cp .:antlr-3.2.jar *.java
java -cp .:antlr-3.2.jar Main


you will see the following output:

BoolExpTree[AND]
. BoolExpTree[true]
. BoolExpTree[||]
. . BoolExpTree[false]
. . BoolExpTree[&&]
. . . BoolExpTree[true]
. . . BoolExpTree[OR]
. . . . BoolExpTree[true]
. . . . BoolExpTree[false]


Regards,

Bart.