{-| Compos compatibility layer. This module serves as a drop-in replacement in some situations for some of the Compos operations. Only the single-type traversals are supported, on normal algebraic data types. Users should also import either "Data.Generics.Uniplate.Data" or "Data.Generics.Uniplate.Direct". Compos is described in the paper: \"A Pattern for Almost Compositional Functions\" by Bjorn Bringert and Aarne Ranta. * <http://doi.acm.org/10.1145/1159803.1159834> * <http://www.cs.chalmers.se/~bringert/publ/composOp/composOp.pdf> -} module Data.Generics.Compos where import Control.Monad import Data.Monoid import Data.Generics.Uniplate.Operations -- | If you want to keep an existing type class class Uniplate a => Compos a where -- | @composOp == 'descend'@ composOp :: Uniplate a => (a -> a) -> a -> a composOp = descend -- | @composOpM == 'descendM'@ composOpM :: (Uniplate a, Monad m) => (a -> m a) -> a -> m a composOpM = descendM -- | @composOpM_ == 'composOpFold' (return ()) (>>)@ composOpM_ :: (Uniplate a, Monad m) => (a -> m ()) -> a -> m () composOpM_ = composOpFold (return ()) (>>) -- | @composOpMonoid = 'composOpFold' mempty mappend@ composOpMonoid :: (Uniplate a, Monoid m) => (a -> m) -> a -> m composOpMonoid = composOpFold mempty mappend -- | @composOpMPlus = 'composOpFold' mzero mplus@ composOpMPlus :: (Uniplate a, MonadPlus m) => (a -> m b) -> a -> m b composOpMPlus = composOpFold mzero mplus -- | Probably replace with 'universe', perhaps 'para' composOpFold :: Uniplate a => b -> (b -> b -> b) -> (a -> b) -> a -> b composOpFold zero combine f = foldr combine zero . map f . children