implementation module while

import StdEnv

:: Gamma :== String -> Int
instance gamma Gamma
where
	put g i v = \i`->if (i == i`) v (g i)
	get g v = g v

emptyGamma :: Gamma
emptyGamma = abort "Undefined variable"

instance eval WhileExpr
where
	eval (i =. v)         = \g->put g i (evali v g)
	eval (If b _ t _ e)   = \g->if (evalb b g) (eval t g) (eval e g)
	eval (a :. b)         = eval b o eval a
	eval x=:(While b _ e) = \g->if (evalb b g) (eval (e :. x) g) g
	eval Skip             = id
	eval (WExpr e)        = eval e

instance evali WhileInt
where
	evali (Int i)  = const i
	evali (Var s)  = flip get s
	evali (a +. b) = \g->evali a g + evali b g
	evali (WInt e) = evali e

instance evalb WhileBool
where
	evalb (Bool b)  = const b
	evalb (a ==. b) = \g->evali a g == evali b g
	evalb (a &. b)  = \g->evalb a g && evalb b g
	evalb (Not a)   = not o evalb a
	evalb (WBool e) = evalb e

Start = (eval ("a" =. Int 42 :. While (Bool False) Do ("b" =. Int 4)) emptyGamma) "a"