Example 2: a question-answering system

Transfer function

• import PGF
  import Arithmetic
  
  transfer :: Tree -> Tree
  transfer = gf . answer . fg
  
  answer :: GQuestion -> GAnswer
  answer (GEven  x) = test even  x
  answer (GOdd   x) = test odd   x
  answer (GPrime x) = test prime x
  
  test :: (Int->Bool) -> GObject -> GAnswer    
  test p (GNumber (GInt x)) = if p x then GYes else GNo
  
  prime n = and [n `mod` d /= 0 | d <-[2..n-1]]
  

• Complete program: Answer.hs