Antlr4 how to build a grammar allowed keywords as identifier

Question

This is a demo code

label:
var id
let id = 10
goto label

If allowed keyword as identifier will be

let:
var var
let var = 10         


        

Answer 1

The simplest way is to define a parser rule for identifiers:

id: ID | VAR | LET;

VAR: 'var';
LET: 'let';
ID: [a-zA-Z] [a-zA-Z0-9]*;

And then use id instead of ID in your parser rules.

A different way is to use ID for identifiers and keywords, and use predicates for disambiguation. But it's less readable, so I'd use the first way instead.