Question

I’ve got task to do and I even dont know how to start. I need to implement AST parser for queries like that one:

((book where publish_date > 2000).author)

In main method it should look like this:

Expression ex = new DotExpression(
   new WhereExpression(
      new NameExpression("book"),
      new NameExpression("publish_date") > 2000
   ),
   new NameExpression("author"));
ex.accept(new ASTVisitor());

That’s only example how to call it. Any advices how to start? Some code examples would be great.

Answer 1

A factory for all those classes would be fine:

public abstract class Expressions {
    public static DotExpression dot(NameExpression lhs, Expression rhs);
    public static BooleanExpression where(Expression lhs, Expression rhs);
    public static NameExpression name(String name);
    public static BooleanExpression gt(Expression lhs, Expression rhs);
}

Usage

 static import Expressions.*;

 ... where(gt(name("publish_date"), value(2000)));