Fix example

sample-programs/working/lambda_calculus-2.crf

@@ -7,19 +7,24 @@ data Exp where
 
 data Val where
     VInt     : Int -> Val
-    VClosure : List (Pair Char Val) -> Char -> Exp -> Val
+    VClosure : Cxt -> Char -> Exp -> Val
 
-lookup : Char -> List (Pair Char Val) -> Val
+data Cxt where 
+    Cxt : List (Pair Char Val) -> Cxt
+
+lookup : Char -> Cxt -> Val
 lookup x cxt = case cxt of
+    Cxt ps => case ps of
         Cons p ps => case p of
             Pair y v => case (asciiCode x) == (asciiCode y) of
                 True  => v
-                False => lookup x ps
+                False => lookup x (Cxt ps)
 
-insert : Char -> Val -> List (Pair Char Val) -> List (Pair Char Val)
-insert x v cxt = Cons (Pair x v) cxt
+insert : Char -> Val -> Cxt -> Cxt
+insert x v cxt = case cxt of
+    Cxt ps => Cxt (Cons (Pair x v) ps)
 
-eval : List (Pair Char Val) -> Exp -> Val
+eval : Cxt -> Exp -> Val
 eval cxt exp = case exp of
     EVar x => case lookup x cxt of
         VInt i             => VInt i
@@ -39,6 +44,6 @@ exp = EApp (EAbs 'x' (EVar 'x')) (EApp (EAbs 'x' (EAdd (EVar 'x') (EInt 100))) (
 -- (λ x . x) (λ x . x + 100) 200
 
 main : Int
-main = case eval Nil exp of
+main = case eval (Cxt Nil) exp of
            VInt i => i