Haskell Error

gistfile1.txt

src/sc.hs:78:35:
    Couldn't match type `M.Map String LispVal' with `[(String, b0)]'
    Expected type: [(String, b0)]
      Actual type: Env
    In the second argument of `lookup', namely `env'
    In the expression: lookup var env
    In the expression:
      case lookup var env of {
        Just value -> True
        Nothing -> False }

sc.hs

 23 type Env = M.Map String LispVal

 76 -- Naive implementation, no need to lookup value
 77 isBound :: Env -> String -> Bool
 78 isBound env var = case lookup var env of
 79                       Just value  -> True
 80                       Nothing     -> False