What's the easiest way to distinguish different input types based on your Antlr grammar?

Question

In my grammar I have rules as below:

set_stmt
:SET  ID (DOT ID)?  TO  setExpr NEWLINE+
;

setExpr
: arithExpr
| ID (DOT ID)?
| STRINGLITERAL
; 

For the different input types as below,

set id to id
set id to ""
set id to id.id
set id to arithExpr

set id.id to id
set id.id to ""
set id.id to id.id
set id.id to arithExpr

I must implement different logics in my visitor class. What's the easiest way for me to do that?

Answer 1

First decompose your grammar:

set_stmt
:SET  ID TO  setExpr NEWLINE+ #setvar
|SET  ID DOT ID  TO  setExpr NEWLINE+ #setatt
;

setExpr
: arithExpr # number
| STRINGLITERAL # string
| ID # getvar
| ID DOT ID #getatt
;

This will generate a visitor with a visit method for each labeled alternative. This enables you to write different code in each visitor method.