ANTLR: expression evaluation with custom object and method

Question

Is it possible to use ANTLR internally in a Java program and use custom classes to execute actual operations ? I would like to be able to parse simple expressions and execute custom operations for them defined in my own Java classes.

Sample expression :

(( AB1 op1 BC2) op2 BB )

AB1, BC2 and BB represent custom Java classes for example MyObj. op1 and op2 are very simple operations and could be thought as + or -

Let's say I have:

interface Operation {
    public MyObj operation(MyObj obj1, MyObj obj2);
}

class SomeOperation implements Operation {
    public MyObj operation(MyObj obj1, MyObj obj2) {

    };
}

class Some2Operation implements Operation {
    public MyObj operation(MyObj obj1, MyObj obj2) {

    };
}

SomeOperation refers to op1 and Some2Operation refers to op2.

Before evaluating the expression of course actual objects for AB1, BC2 and BB are assigned.

If there's easier/simpler way to accomplish this than using ANTLR please let me know.

EDIT: Continues here...

grammar MyTest;

ID: [a-z]+;

Operator_I: 'I';
Operator_U: 'U';


prog:   (expr)* #myProg;
expr:   expr op=(Operator_I | Operator_U) expr  #myExpr
    | ID    #myID
    |   '(' expr ')' #myWithPar
    ;


import org.antlr.v4.runtime.misc.NotNull;
import org.antlr.v4.runtime.tree.TerminalNode;

import java.util.*;

public class EvalVisitor extends MyTestBaseVisitor<Value> {

    @Override
    public Value visitMyProg(MyTestParser.MyProgContext ctx) {
        // TODO Auto-generated method stub
        System.out.println("prog:"+ctx.getText());
        return super.visitMyProg(ctx);
    }

    @Override
    public Value visitMyWithPar(MyTestParser.MyWithParContext ctx) {
        // TODO Auto-generated method stub
        System.out.println("par:"+ctx.getText());
        return super.visitMyWithPar(ctx);
    }

    @Override
    public Value visitMyID(MyTestParser.MyIDContext ctx) {
        // TODO Auto-generated method stub
        System.out.println("id:"+ctx.getText());
        return super.visitMyID(ctx);
    }

    @Override
    public Value visitMyExpr(MyTestParser.MyExprContext ctx) {
        // TODO Auto-generated method stub
        System.out.println("expr:"+ctx.getText());
        return super.visitMyExpr(ctx);
    }

    private Map<String, Value> memory = new HashMap<String, Value>();   
    private Map<String, Value> values = new HashMap<String, Value>();

    public EvalVisitor() {
        values.put("a", new Value(new Double(5)));
        values.put("u", new Value(new Double(9)));

    }

}

 public static void main(String[] args) throws Exception {
        MyTestLexer lexer = new MyTestLexer(new ANTLRFileStream("c:\\test.mu"));
        MyTestParser parser = new MyTestParser(new CommonTokenStream(lexer));
        ParseTree tree = parser.prog();
        EvalVisitor visitor = new EvalVisitor();
        visitor.visit(tree);
    }

test.mu contains:

(aIu)U(aUu)

output of the program:

prog:(aIu)U(aUu)
expr:(aIu)U(aUu)
par:(aIu)
expr:aIu
id:a
id:u
par:(aUu)
expr:aUu
id:a
id:u

score 1 · Accepted Answer · edited May 23 '17 at 12:21

1

ANTLR only provides a parser for your language. An actual interpreter (evaluating your input) is up to you. You can use ANTLR's visitors to easily create an interpreter. A demo can be found in this Q&A: If/else statements in ANTLR using listeners

If you don't want to write the interpreter yourself, you'll need to find a library that suits your needs. See this Q&A for a list of available libraries: Evaluating a math expression given in string form

edited May 23 '17 at 12:21

Community

1
1

answered May 27 '15 at 06:43

Bart Kiers

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Added some more data in main question area. I got basic things done quite quickly. Thanks a lot for that. Thanks! I'm wondering about what to do in actual callback functions visitMyExpr etc. Should I save value of 'expr' in hashtable or what ? Also is my grammar correct ? I want also to do this: ((aUb)Ic) and now it seems it will omit the last 'Ic)' ? – knocker_d May 27 '15 at 12:06
@knocker_d, I've not the time right now. Instead of editing your original question (which was a short question, and I therefor answered it), I recommend asking a new question instead. Good luck! – Bart Kiers May 27 '15 at 16:11

ANTLR: expression evaluation with custom object and method

1 Answers1