content: {-|
      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.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, Applicative 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
  