USING: classes.tuple kernel prettyprint sequences ;

TUPLE: worker first last occupation ;
TUPLE: lawyer < worker ;
TUPLE: dentist < worker ;

: field-sets-class ( cls -- sub )
  dup occupation>> {
    { "lawyer" [ lawyer ] }
    { "dentist" [ dentist ] }
    [ drop worker ]
  } case
  [ tuple>array [ ] each ] dip boa nip ;

: field-sets-class-2 ( cls -- sub )
  dup occupation>> {
    { "lawyer" [ lawyer ] }
    { "dentist" [ dentist ] }
    [ drop "fake-obj" worker ]
  } case
  [ tuple>array [ ] each ] dip boa nip ;

"j" "mack" "lawyer" worker boa
field-sets-class .