module Environments where

{- Definitions from the Environments slides -}

data Value = I Int | R Float -- or, whatever

data Env = Env (String -> Value) 

tweek :: (String,Value) -> Env -> Env
tweek (x,v) (Env rho) = Env (\ n -> if n==x then v else rho n) 

tweekList :: [(String,Value)] -> Env -> Env
tweekList bindings env = foldr tweek env bindings 

emptyenv :: Env
emptyenv = Env (\ x -> I 0) 

extendenv :: [String] -> [Value] -> Env -> Env
extendenv vars vals (Env rho) = tweekList (zip vars vals) (Env rho) 

applyenv :: Env -> String -> Value
applyenv (Env rho) x = rho x 

-----------------------------------
-- Making unbound things unbound --
-----------------------------------
data Env1 = Env1 (String -> Maybe Value) 

tweek1 :: (String,Value) -> Env1 -> Env1
tweek1 (x,v) (Env1 rho) = Env1 (\ n -> if n==x then Just v else rho n) 

tweekList1 :: [(String,Value)] -> Env1 -> Env1
tweekList1 bindings env = foldr tweek1 env bindings 

emptyenv1 :: Env1
emptyenv1 = Env1 (\ x -> Nothing) 

extendenv1 :: [String] -> [Value] -> Env1 -> Env1
extendenv1 vars vals (Env1 rho) = tweekList1 (zip vars vals) (Env1 rho) 

applyenv1 :: Env1 -> String -> Value
applyenv1 (Env1 rho) x = case rho x of
                              (Just v) -> v
                              Nothing  -> error (x ++ " is unbound")

-----------------------------------
-- Making unbound things unbound --
-----------------------------------
data Env2 val = Env2 (String -> Maybe val) 

tweek2 :: (String,val) -> Env2 val -> Env2 val
tweek2 (x,v) (Env2 rho) = Env2 (\ n -> if n==x then Just v else rho n) 

tweekList2 :: [(String,val)] -> Env2 val -> Env2 val
tweekList2 bindings env = foldr tweek2 env bindings 

emptyenv2 :: Env2 val
emptyenv2 = Env2 (\ x -> Nothing) 

extendenv2 :: [String] -> [val] -> Env2 val -> Env2 val
extendenv2 vars vals (Env2 rho) = tweekList2 (zip vars vals) (Env2 rho) 

applyenv2 :: Env2 val -> String -> val
applyenv2 (Env2 rho) x = case rho x of
                              (Just v) -> v
                              Nothing  -> error (x ++ " is unbound")

data FunVal = DefineYourself
type Zee = Env2 Int
type Rho = Env2 Int
type Phi = Env2 FunVal

data Exp = SeeTheSlides
data ExpStore = ES Exp Zee Phi Rho

data Store a = Str a Zee Phi Rho