Cactus example made even simpler

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

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

expr
  = Op..    ::= expr op expr
  | Number.. ::= number
  | ..       ::= '(' expr ')' ;

%expand op ::= '+' | '-' | '*' | '/' ;

• The %expand directive can be used to avoid conflicts in LR parsers that can arise when refactoring the grammar.
• The abstract syntax can be omitted from a rule.