[antlr-interest] What to do when you need to semantically validate an expression?

[Bill Mayfield]

Hi,

I need to create a formula language for our product. The formulas 
entered need to be translated to SQL statements that can be executed 
against our database.

Basically I would create a lexer and parser for the formula language 
using ANTLR so that I can build an expression tree. But then I'm 
somewhat *stuck*.

1. Do I let ANTLR create an AST automatically or do I create a tree by 
hand with more meaningful types like Expression, Sum, etc...
2. The parsed result needs to be semantically validated. I presume I 
need to write custom validation logic in each type for this??? This 
might answer question 1?

for instance: (pseudo-code)

public class Sum
{
    private Expression left;
    private Expression right;

    public void validate()
    {
       //validate whether left and right are of correct datatypes
    }
}

3. Would it be better to write a translater by hand to translate the 
expression tree to SQL or would it be better to use a treewalker to do 
this?


I'm new to ANTLR, have just read (most of) the spec, and I could use 
some guidance.


Thanks!