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diff --git a/expr/exist/while.icl b/expr/exist/while.icl
new file mode 100644
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--- /dev/null
+++ b/expr/exist/while.icl
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+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"