module Happstack.Data.GOps where
import Data.Generics hiding (GT)
import Control.Monad.Reader
import Control.Monad.State
import Data.Maybe
gSet :: (Data b, Typeable a) => a -> b -> b
gSet = gReplace . const
gReplace :: (Typeable a, Data b) => (a -> a) -> b -> b
gReplace f x = everywhere (mkT f) x
gFind :: (MonadPlus m, Data a, Typeable b) => a -> m b
gFind = msum . map return . listify (const True)
gFind' :: (Data a, Typeable b) => a -> b
gFind' = fromJust . gFind
gModify :: (MonadState s m,Typeable a,Data s) => (a->a) -> m ()
gModify = modify . gReplace
gAsk :: (Data r, Typeable a, MonadReader r m, MonadPlus n) =>
(a -> n b) -> m (n b)
gAsk f = do st <- ask
let y = gFind st
return $ maybe mzero f y
gGet :: (Data s, Typeable a, MonadState s m, MonadPlus n) =>
(a -> n b) -> c -> m (n b)
gGet f _ = do st <- get
let y = gFind st
return $ maybe mzero f y