haskell/Env.hs

   1 module Env
   2 ( Env, env_new, env_bind, env_get, env_set )
   3 where
   4
   5 import Data.IORef (modifyIORef, newIORef, readIORef)
   6 import qualified Data.Map  as Map
   7
   8 import Types
   9
  10 -- The Env type si defined in Types module to avoid dep cycle.
  11
  12 env_new :: Env -> IO Env
  13 env_new outer = (: outer) <$> newIORef (Map.fromList [])
  14
  15 --  True means that the actual arguments match the signature.
  16 env_bind :: Env -> [String] -> [MalVal] -> IO Bool
  17 env_bind env (k : ks) (v : vs) | k /= "&" = do
  18     env_set env k v
  19     env_bind env ks vs
  20 env_bind env ["&", k] vs = do
  21     env_set env k $ toList vs
  22     return True
  23 env_bind _ [] [] = return True
  24 env_bind _ _ _ = return False
  25
  26 env_get :: Env -> String -> IO (Maybe MalVal)
  27 env_get [] _ = return Nothing
  28 env_get (ref : outer) key = do
  29     hm <- readIORef ref
  30     case Map.lookup key hm of
  31         Nothing -> env_get outer key
  32         justVal -> return justVal
  33
  34 env_set :: Env -> String -> MalVal -> IO ()
  35 env_set (ref : _) key val = modifyIORef ref $ Map.insert key val
  36 env_set [] _ _ = error "assertion failed in env_set"