kvskvskvs.hs

import           Control.Monad.State (StateT)
import qualified Control.Monad.State as State
import           Data.Map (Map)
import qualified Data.Map as Map
import           Data.IORef (IORef)
import qualified Data.IORef as IORef

data AbstractKVS m k v = AbstractKVS 
  { kvsPut :: k -> v -> m ()
  , kvsGet :: k -> m (Maybe v)
  , kvsModify :: (Maybe v -> Maybe v) -> k -> m ()
  }

stateTKVS :: (Ord k, Monad m) => AbstractKVS (StateT (Map k v) m) k v
stateTKVS = AbstractKVS
  { kvsPut    = \k v -> State.modify (Map.insert k v)
  , kvsGet    = \k   -> State.gets (Map.lookup k)
  , kvsModify = \f k -> State.modify (Map.alter f k)
  }

iorefMapKVS :: (Ord k) => IORef (Map k v) -> AbstractKVS IO k v
iorefMapKVS s = AbstractKVS
  { kvsPut    = \k v -> IORef.modifyIORef' s (Map.insert k v)
  , kvsGet    = \k   -> fmap (Map.lookup k) (IORef.readIORef s) 
  , kvsModify = \f k -> IORef.modifyIORef' s (Map.alter f k)
  }

test0 :: Monad m => AbstractKVS m String Int -> m Int
test0 (AbstractKVS put get modify) = do
  x <- get "7"
  put "8" 5
  Just i <- get "8"
  return i

runtests :: IO ()
runtests = do
  print =<< State.evalStateT (test0 stateTKVS) Map.empty
  print =<< test0 . iorefMapKVS =<< IORef.newIORef Map.empty