Now when a var is evaluated, the new evaluation replaces the old

src/Evaluator.hs

@@ -15,8 +15,9 @@ base = M.fromList [
 
 eval :: Env -> Expr -> (Env, Expr)
 eval env (IntE x)      = (env, IntE x)
-eval env (VarE v)      = eval env $ env M.! v
-eval env (SetE v expr) = (M.insert v expr env, expr)
+eval env (VarE v)      = (M.insert v nExpr nEnv, nExpr)
+  where (nEnv, nExpr) = eval env $ env M.! v
+eval env (SetE v expr) = (M.insert v expr env, NilE)
 eval env NilE          = (env, NilE)
 
 --apply :: Proc -> Args -> Expr

src/ExprType.hs

@@ -4,9 +4,9 @@ data Expr = IntE Integer
           | VarE String
           | ProcedureE String [Expr]
           | SetE String Expr
-          | NilE
+          | NilE deriving (Show)
 
-instance Show Expr where
-  show (IntE x) = show x
-  show (VarE x) = x ++ " ; var"
-  show NilE     = "nil"
+-- instance Show Expr where
+--   show (IntE x) = show x
+--   show (VarE x) = x ++ " ; var"
+--   show NilE     = "nil"