token Num='<number>';
token Plus='+' Minus='-' Star='*' Slash='/';
token LPar='(' RPar=')';
token Whitespace;

skip Whitespace;

start calc;

calc: expr;
expr:
  expr ('*' | '/') expr
| expr ('+' | '-') expr
| atomic
;
atomic: literal | paren;
literal: Num;
paren: '(' expr ')';