gf-3.10: gf-book/examples/chapter7/Query.gf

abstract Query = {
  flags startcat=Question ;
  cat 
    Answer ; Question ; Object ;
  fun 
    Even   : Object -> Question ;
    Odd    : Object -> Question ;
    Prime  : Object -> Question ;
    Number : Int -> Object ;
    Yes    : Answer ;
    No     : Answer ;
}