old/afp/a12/cashModel.icl

   1 implementation 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 class euro a :: a -> Euro
  13 instance euro Product where
  14         euro Pizza = euro (4,99)
  15         euro Beer  = euro (0,65)
  16         euro _     = euro 1
  17
  18 instance euro Int where euro e = {euro = e, cent = 0}
  19 instance euro (Int, Int) where euro (e,c) = {euro = e, cent = c}
  20 instance euro [e] | euro e where euro l = sum (map euro l)
  21 instance euro Euro where euro e = e
  22 instance + Euro where + x y = fromCents (toCents x + toCents y)
  23 instance - Euro where - x y = fromCents (toCents x - toCents y)
  24 instance zero Euro where zero = {euro = 0, cent = 0}
  25 derive gEq Euro, Product
  26 instance == Product where (==) p q = p === q
  27 instance == Euro where (==) p q = p === q
  28
  29 instance ~ Euro where ~ e = {euro = ~e.euro, cent = ~e.cent}
  30
  31 toCents :: Euro -> Int
  32 toCents e = if (e.euro < 0 || e.cent < 0) (~) id (abs e.euro*100 + abs e.cent)
  33
  34 fromCents :: Int -> Euro
  35 fromCents c = if (c < 0) (~) id {euro=abs c / 100, cent=abs c rem 100}
  36
  37 model :: [Product] Action -> ([Product],[Euro])
  38 model list (Add p) = ([p:list],[euro p])
  39 model list (Rem p) | isMember p list
  40  = (removeMember p list,[~ (euro p)])
  41  = (list,[])
  42 model list Pay = ([],[euro list])