example_final.rb

entityDef returns [ entity ]
  : 'entity' entityName '{' { 
      entity = Entity.new($entityName.text, 
                          $entityName.start.line)
    }
      (attrib = attribDef { entity << attrib } )+
    '}'
  ;

example_first.rb

entityDef returns [ entity ]
  : 'entity' entityName '{' { 
      entity = Entity.new($entityName.text, 
                          $entityName.start.line)
    }
      attribDef+
    '}'
  ;

attribDef returns [ attrib ]
  : ID ':' TYPE {
     attrib = Attribute.new($ID.text, 
                            $TYPE.text.downcase.to_sym, 
                            $ID.line)
    }
  ;

input

entity User {
  first_name: String
  last_name: String
  age: Integer
}