a11/mart/skeleton11.icl

   1 module skeleton11
   2 //Mart Lubbers s4109503
   3 //Charlie Gerhardus s3050009
   4 import StdEnv
   5
   6 :: Prog :== [Instr]
   7 :: Instr = Write Expr | Atomic [Instr]
   8 :: Expr = Int   Int
   9         | Plus  Expr Expr
  10         | Times Expr Expr
  11         | Read
  12
  13 possibleResults :: [Prog] -> [Int]
  14 possibleResults x = produce x 0
  15
  16 produce :: [Prog] Int -> [Int]
  17 produce x i
  18 | all (isEmpty) x = [i]
  19 = flatten [produce (updateAt idx ys x) (eval y i)\\(idx, [y:ys])<-zip2 [0..] x]
  20
  21 eval :: Instr Int -> Int
  22 eval (Write (Int i)) s = i
  23 eval (Write (Plus e1 e2)) s = eval (Write e1) s + eval (Write e2) s
  24 eval (Write (Times e1 e2)) s = eval (Write e1) s * eval (Write e2) s
  25 eval (Write Read) s = s
  26 eval (Atomic x) s = hd (produce [x] s)
  27
  28 prog0 = [Write (Int 12), Write (Plus Read (Int 1))]
  29 prog1 = [Write (Times Read (Int 2))]
  30 test0 = [prog0]
  31 test1 = [prog0, prog1]
  32
  33 Start = 0
  34 /* Writing the semantics in clean is advantageous because you can execute the
  35  * code, have it type checked and it is very readable for a programmer.
  36  *
  37  * Disadvantages might be that it might be harder to prove stuff. Also
  38  * mathematic notation is generally more concise.
  39  *
  40  * Some things are modelled very difficultly in a functional language. For
  41  * example file io, parallel processes or user interaction.
  42 */