{- | This module retained Haskell 98 compatability, but users who are happy with multi-parameter type classes should look towards "Data.Generics.Biplate". The only function missing from "Data.Generics.Uniplate" is 'fold', as it can be constructed from 'children' and has little meaning in a multi-typed setting. All operations, apart from 'childrenOn' should perform identically to their non @On@ counterparts. -} module Data.Generics.UniplateOn( module Data.Generics.Uniplate, module Data.Generics.UniplateOn ) where import Data.Generics.Uniplate import Control.Monad(liftM) import Data.List(inits,tails) -- * Types -- | Return all the top most children of type @to@ within @from@. -- -- If @from == to@ then this function should return the root as the single -- child. type BiplateType from to = from -> ([to], [to] -> from) -- * Operations -- ** Queries universeOn :: Uniplate to => BiplateType from to -> from -> [to] universeOn biplate x = concatMap universe $ fst $ biplate x -- | Return the children of a type. If @to == from@ then it returns the -- original element (in constract to 'children' childrenOn :: Uniplate to => BiplateType from to -> from -> [to] childrenOn biplate x = fst $ biplate x -- ** Transformations transformOn :: Uniplate to => BiplateType from to -> (to -> to) -> from -> from transformOn biplate f x = generate $ map (transform f) current where (current, generate) = biplate x transformOnM :: (Monad m, Uniplate to) => BiplateType from to -> (to -> m to) -> from -> m from transformOnM biplate f x = liftM generate $ mapM (transformM f) current where (current, generate) = biplate x rewriteOn :: Uniplate to => BiplateType from to -> (to -> Maybe to) -> from -> from rewriteOn biplate f x = generate $ map (rewrite f) current where (current, generate) = biplate x rewriteOnM :: (Monad m, Uniplate to) => BiplateType from to -> (to -> m (Maybe to)) -> from -> m from rewriteOnM biplate f x = liftM generate $ mapM (rewriteM f) current where (current, generate) = biplate x descendOn :: Uniplate to => BiplateType from to -> (to -> to) -> from -> from descendOn biplate f x = generate $ map (descend f) current where (current, generate) = biplate x descendOnM :: (Monad m, Uniplate to) => BiplateType from to -> (to -> m to) -> from -> m from descendOnM biplate f x = liftM generate $ mapM (descendM f) current where (current, generate) = biplate x -- ** Other contextsOn :: Uniplate to => BiplateType from to -> from -> [(to, to -> from)] contextsOn biplate x = concat [f pre b post | (pre,b:post) <- zip (inits current) (tails current)] where (current, generate) = biplate x f pre x post = [(cur, \new -> generate (pre ++ [new] ++ post)) | (cur,gen) <- contexts x] -- * Helper for writing instances -- | Used for defining instances @UniplateFoo a => UniplateFoo [a]@ uniplateOnList :: BiplateType a b -> BiplateType [a] b uniplateOnList f [] = ([], \[] -> []) uniplateOnList f (x:xs) = (a ++ as, \ns -> let (n1,n2) = splitAt (length a) ns in b n1 : bs n2) where (a , b ) = f x (as, bs) = uniplateOnList f xs