try
   F=$(fun x, 1)
   printvln($F)
   println($"Arity of F is $(F.arity)")
   if $(not $(eq $(F.arity), 1))
      eprintln($"Arity of F is $(F.arity), when 1 was expected")
      exit 1
default
   eprintln($"Could not compute the arity of a \$(fun) expression")
   exit 1
