old/expr/exist/while.icl

   1 implementation module while
   2
   3 import StdEnv
   4
   5 :: Gamma :== String -> Int
   6 instance gamma Gamma
   7 where
   8         put g i v = \i`->if (i == i`) v (g i)
   9         get g v = g v
  10
  11 emptyGamma :: Gamma
  12 emptyGamma = abort "Undefined variable"
  13
  14 instance eval WhileExpr
  15 where
  16         eval (i =. v)         = \g->put g i (evali v g)
  17         eval (If b _ t _ e)   = \g->if (evalb b g) (eval t g) (eval e g)
  18         eval (a :. b)         = eval b o eval a
  19         eval x=:(While b _ e) = \g->if (evalb b g) (eval (e :. x) g) g
  20         eval Skip             = id
  21         eval (WExpr e)        = eval e
  22
  23 instance evali WhileInt
  24 where
  25         evali (Int i)  = const i
  26         evali (Var s)  = flip get s
  27         evali (a +. b) = \g->evali a g + evali b g
  28         evali (WInt e) = evali e
  29
  30 instance evalb WhileBool
  31 where
  32         evalb (Bool b)  = const b
  33         evalb (a ==. b) = \g->evali a g == evali b g
  34         evalb (a &. b)  = \g->evalb a g && evalb b g
  35         evalb (Not a)   = not o evalb a
  36         evalb (WBool e) = evalb e
  37
  38 instance print WhileExpr
  39 where
  40         print (i =. v)         = i +++ " := " +++ print v
  41         print (If b _ t _ e)   = "If " +++ print b +++ " then " +++ print t +++ " else " +++ print e
  42         print (a :. b)         = print a +++ "; " +++ print b
  43         print x=:(While b _ e) = "While " +++ print b +++ " do " +++ print e
  44         print Skip             = "Skip"
  45         print (WExpr e)        = print e
  46
  47 instance print WhileInt
  48 where
  49         print (Int i)  = toString i
  50         print (Var s)  = s
  51         print (a +. b) = print a +++ " + " +++ print b
  52         print (WInt e) = print e
  53
  54 instance print WhileBool
  55 where
  56         print (Bool b)  = toString b
  57         print (a ==. b) = print a +++ " = " +++ print b
  58         print (a &. b)  = print a +++ " && " +++ print b
  59         print (Not a)   = "!" +++ print a
  60         print (WBool e) = print e
  61
  62 Start = (eval ("a" =. Int 42 :. While (Bool False) Do ("b" =. Int 4)) emptyGamma) "a"