Cactus example made slightly simpler

.blank = [" \t\f\b\v\r\n"]
.number :: Int = ['0'..'9']+

%left.6 = '+', '-'
%left.7 = '*', '/'

expr
  = Add..    ::= expr '+' expr
  | Sub..    ::= expr '-' expr
  | Mul..    ::= expr '*' expr
  | Div..    ::= expr '/' expr
  | Number.. ::= number
  | ..       ::= '(' expr ')' ;