diff --git a/src/Evaluator.hs b/src/Evaluator.hs
index b5b8bd6..d6baaa0 100644
--- a/src/Evaluator.hs
+++ b/src/Evaluator.hs
@@ -5,23 +5,21 @@ import ExprType
 
 type Env = M.Map String Expr
 type Proc = String
-type Args = [Expr]
 
-eval :: Expr -> Expr
-eval (IntE x)             = IntE x
-eval (VarE v)             = VarE v
-eval (DefinitionE v exp)  = NilE
-eval (ProcedureE p args)  = apply p args
-eval NilE                 = NilE
-
-apply :: Proc -> Args -> Expr
-apply p args
-    | p == "+" = builtinPlus $ map eval args
 -- TODO: create a separated file for builtinProcs
 -- TODO: create a BuiltinProc or something like that in data Expr, and make + a builtin proc
 -- TODO: create enviroments
 
-builtinPlus :: [Expr] -> Expr
-builtinPlus [IntE x, IntE y] = IntE $ x + y
-builtinPlus ((IntE x):xs) = IntE $ x + n
-  where (IntE n) = builtinPlus xs
+base :: Env
+base = M.fromList [
+  ("test-var", IntE 10)
+  ]
+
+eval :: Env -> Expr -> (Env, Expr)
+eval env (IntE x)      = (env, IntE x)
+eval env (VarE v)      = (env, env M.! v)
+eval env (SetE v expr) = (M.insert v expr env, NilE)
+eval env NilE          = (env, NilE)
+
+--apply :: Proc -> Args -> Expr
+--apply p args
diff --git a/src/ExprParser.hs b/src/ExprParser.hs
index da4599e..36cc1b0 100644
--- a/src/ExprParser.hs
+++ b/src/ExprParser.hs
@@ -49,11 +49,11 @@ nilE = do
 defineE :: GenParser Token st Expr
 defineE = do
   _ <- parseLeftParenT
-  _ <- parseDefineT
+  _ <- parseSetT
   (VarT var) <- parseVarT
   expr <- expressionFromTokens
   _ <- parseRightParenT
-  return $ DefinitionE var expr
+  return $ SetE var expr
 
 ------------------------------------------------------------
 
@@ -68,8 +68,8 @@ parseLeftParenT = satisfyT (== LeftParenT)
 parseRightParenT :: GenParser Token st Token
 parseRightParenT = satisfyT (== RightParenT)
 
-parseDefineT :: GenParser Token st Token
-parseDefineT = satisfyT (== DefineT)
+parseSetT :: GenParser Token st Token
+parseSetT = satisfyT (== SetT)
 
 parseNilT :: GenParser Token st Token
 parseNilT = satisfyT (== NilT)
diff --git a/src/ExprType.hs b/src/ExprType.hs
index 558ac67..97635b5 100644
--- a/src/ExprType.hs
+++ b/src/ExprType.hs
@@ -3,7 +3,7 @@ module ExprType where
 data Expr = IntE Integer
           | VarE String
           | ProcedureE String [Expr]
-          | DefinitionE String Expr
+          | SetE String Expr
           | NilE
 
 instance Show Expr where
diff --git a/src/Main.hs b/src/Main.hs
index 5a7138b..fa79d53 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -2,7 +2,6 @@ module Main where
 
 import Evaluator
 import ExprParser
-import Text.Parsec.Error
 import Control.Monad
 import Data.Maybe
 import System.Console.Haskeline
@@ -10,21 +9,21 @@ import System.Console.Haskeline
 main :: IO ()
 main = do
   putStrLn logo
-  runInputT defaultSettings loop
-  where loop = do
+  runInputT defaultSettings repl
+
+repl :: InputT IO ()
+repl = do
+  repl' base
+  where repl' env = do
           line <- getInputLine "cherry> "
           unless (isNothing line) $ do
-            let r = readEval $ fromJust line
-            outputStrLn $ case r of
-              Right res -> res
-              Left err -> show err
-            loop
-
-readEval :: String -> Either ParseError String
-readEval s = do
-  expr <- parseExpression s
-  let result = eval expr
-  return $ show result
+            let expr = parseExpression $ fromJust line
+            let (nEnv, out) = case expr of
+                  (Left err)    -> (env, show err)
+                  (Right expr') -> let (env', nExp) = eval env expr'
+                                   in (env', show nExp)
+            outputStrLn out
+            repl' nEnv
 
 logo :: String
 logo = unlines ["","  /\\", " |  \\", " @   @",""]
diff --git a/src/TokenParser.hs b/src/TokenParser.hs
index 8900e6d..8d31055 100644
--- a/src/TokenParser.hs
+++ b/src/TokenParser.hs
@@ -13,7 +13,7 @@ parseTokens = do
     return tokns
 
 anyLispToken :: GenParser Char st Token
-anyLispToken = leftParenT <|> rightParenT <|> try nilT <|> try defineT <|> varT <|> intT
+anyLispToken = leftParenT <|> rightParenT <|> try nilT <|> try setT <|> varT <|> intT
 
 ------------------------------------------------------------
 
@@ -28,8 +28,8 @@ leftParenT = char '(' >> return LeftParenT
 rightParenT :: GenParser Char st Token
 rightParenT = char ')' >> return RightParenT
 
-defineT :: GenParser Char st Token
-defineT = caseInsensitiveString "define" >> return DefineT
+setT :: GenParser Char st Token
+setT = caseInsensitiveString "set!" >> return SetT
 
 nilT :: GenParser Char st Token
 nilT = caseInsensitiveString "nil" >> return NilT
diff --git a/src/TokenType.hs b/src/TokenType.hs
index b357518..25a9a27 100644
--- a/src/TokenType.hs
+++ b/src/TokenType.hs
@@ -2,7 +2,7 @@ module TokenType where
 
 data Token = LeftParenT
            | RightParenT
-           | DefineT
+           | SetT
            | VarT String
            | IntT Integer
            | NilT