afp/a12/cashModel.dcl

   1 definition module cashModel
   2 /*
   3         Pieter Koopman, Radboud University, 2017 -2018
   4         pieter@cs.ru.nl
   5         Advanced programming
   6
   7         A simple state model for an automated cash register
   8 */
   9
  10 import StdEnv, Data.GenEq
  11
  12 :: Euro = {euro :: Int, cent :: Int}
  13 :: Product = Pizza | Beer | Cola
  14 :: Action = Add Product | Rem Product | Pay
  15
  16 class euro a :: a -> Euro
  17 instance euro Product, Euro
  18 instance euro Int, (Int, Int), [e] | euro e
  19 instance + Euro
  20 instance - Euro
  21 instance zero Euro
  22 derive gEq Euro
  23 instance ~ Euro
  24 instance == Euro, Product
  25
  26 model :: [Product] Action -> ([Product],[Euro])