Base on the correct compiler desc on https://github.com/pa-ba/calc-comp Here is the source code module Lambda_define ( Name, Expr, eval )where import Prelude hiding (null, lookup, map, filter) import Data.HashMap.Lazy type Name = [Char] data Expr = Val Int | Add [Expr] | Var Name | Abs Name Expr | App Expr Expr | Define Name Expr | Begin [Expr] | Let (Name, Expr) Expr data Env = Root | Env { current :: HashMap Name Value, parent :: Env } data Value = Num Int | Clo Name Expr Env envLookup :: Name -> Env -> Value envLookup n Root = Num 10000 --- fix it envLookup n env = case lookup n (current env) of Just v -> v otherwise -> envLookup n (parent env) --------------- setvar :: Name -> Value -> Env -> Env setvar n v Root = Env{current=fromList [(n, v)] , parent=Root } setvar n v Env{current=c, parent=p} = Env{current=(insert n v c), parent=p } eval :: Expr -> Env -> (Value, Env) eval (Val n) e = (Num n , e) eval (Add [x , y]) e = case eval x e of (Num n, e') -> case eval y e of (Num m, e1') -> (Num (n+m), e) eval (Add [x]) e = case eval x e of (Num n, e') -> (Clo "y" (Add [(Val n), (Var "y")]) e' , e) eval (Var n) e = (envLookup n e, e) eval (Abs n x) e = (Clo n x e, e) eval (App x y) e = case eval x e of (Clo n' x' e', env') -> case eval y e of (vy, e'') -> (fst (eval x' (Env (fromList [(n', vy)]) e')), e ) --- the saved clojure env can't be changed eval (Define n e) env = case eval e env of (v, e') -> (Num 0, setvar n v env) --- fix me why 0 eval (Let (n, e1) e2) env = ------ Let should don't chanve the env (fst (eval e2 (Env (fromList [(n, (fst (eval e1 env)))]) env)), env) eval (Begin xs) e = case length xs of 0 -> (Num 0, Root) -- never come here 1 -> case eval (xs !! 0) e of (v, e') -> (v, e') n -> case eval (Begin (take (n - 1) xs)) e of (v, e') -> eval (last xs) e' test1 = eval (Begin [(Define "z" (Val 1)), (Define "y" (Abs "x" (Add [(Var "z"), (Var "x")]))), (Define "x" (Val 7)), (Define "z" (Val 90)), (Add [(Val 5), (App (Var "y") (Val 8))])]) Root test2 = eval (Begin [(Define "z" (Val 1)), (Define "y" (Abs "x" (Add [(Var "z"), (Var "x")]))), (Define "x" (Val 7)), (Let ("z", (Val 90)) (Add [(Val 5), (App (Var "y") (Val 8))])) ]) Root In case you want to see the total program. I put it into https://github.com/jiamo/correct_compiler/blob/master/src/Lambda_define.hs Here is my problem: I want test1 return (Num 103) I want test2 return (Num 14) But now it both return (Num 14) One problem I can figure out that "the eval of Define return a new env can't change the old env" Any one have suggests?