Moved Enviroment into a separate file

cherry-lisp.cabal

@@ -22,7 +22,8 @@ executable cherry
                        Parser,
                        TokenType,
                        Lexer,
-                       Evaluator
+                       Evaluator,
+                       Enviroment
 
   build-depends:       base >= 4.7 && < 5,
                        containers,

src/Enviroment.hs

@@ -0,0 +1,19 @@
+module Enviroment where
+
+import qualified Data.Map as M
+import ExprType
+import Data.Maybe
+
+data Enviroment = Enviroment (M.Map String Expr) (Maybe Enviroment)
+
+base :: Enviroment
+base = Enviroment (M.fromList [
+  ("test-var", IntE 10)
+  ]) Nothing
+
+lookupVar :: Enviroment -> String -> Maybe Expr
+lookupVar (Enviroment menv upperEnv) var = let mExpr = M.lookup var menv in
+  if isNothing mExpr then upperEnv >>= (`lookupVar` var) else mExpr
+
+insertVar :: Enviroment -> String -> Expr -> Enviroment
+insertVar (Enviroment menv u) var expr = Enviroment (M.insert var expr menv) u

src/Evaluator.hs

@@ -1,22 +1,16 @@
 module Evaluator where
 
-import qualified Data.Map as M
 import ExprType
-
-type Env = M.Map String Expr
+import Enviroment
+import Data.Maybe
 
 -- TODO: create a separated file for builtinProcs
 -- TODO: create a BuiltinProc or something like that in data Expr, and make + a builtin proc
 
-base :: Env
-base = M.fromList [
-  ("test-var", IntE 10)
-  ]
-
-eval :: Env -> Expr -> (Env, Expr)
+eval :: Enviroment -> Expr -> (Enviroment, Expr)
 eval env i@(IntE _)    = (env, i)
-eval env (VarE v)      = eval env $ env M.! v
-eval env (SetE v expr) = (M.insert v expr env, NilE)
+eval env (VarE v)      = eval env $ fromJust $ lookupVar env v
+eval env (SetE v expr) = (insertVar env v expr, NilE)
 eval env (QuotedE e)    = (env, e)
 eval env (ConsE car cdr) = (env, apply car cdr)
 eval env NilE          = (env, NilE)

src/ExprType.hs

@@ -5,7 +5,8 @@ data Expr = IntE Integer
           | SetE String Expr
           | ConsE Expr Expr
           | QuotedE Expr
-          | NilE deriving (Show)
+          | NilE
+          deriving (Show)
 
 -- instance Show Expr where
 --   show (IntE x) = show x

src/Main.hs

@@ -1,6 +1,7 @@
 module Main where
 
 import Evaluator
+import Enviroment
 import Parser
 import Control.Monad
 import Data.Maybe