    {-|
        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 :: (a -> a) -> a -> a
    composOp = (a -> a) -> a -> a
    forall on. Uniplate on => (on -> on) -> on -> on
    descend

    -- | @composOpM == 'descendM'@
    composOpM :: (Uniplate a, Monad m) => (a -> m a) -> a -> m a
    composOpM :: (a -> m a) -> a -> m a
    composOpM = (a -> m a) -> a -> m a
    forall on (m :: * -> *).
    (Uniplate on, Monad m) =>
    (on -> m on) -> on -> m on
    descendM

    -- | @composOpM_ == 'composOpFold' (return ()) (>>)@
    composOpM_ :: (Uniplate a, Monad m) => (a -> m ()) -> a -> m ()
    composOpM_ :: (a -> m ()) -> a -> m ()
    composOpM_ = m () -> (m () -> m () -> m ()) -> (a -> m ()) -> a -> m ()
    forall a b. Uniplate a => b -> (b -> b -> b) -> (a -> b) -> a -> b
    composOpFold (() -> m ()
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()) m () -> m () -> m ()
    forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
    (>>)

    -- | @composOpMonoid = 'composOpFold' mempty mappend@
    composOpMonoid :: (Uniplate a, Monoid m) => (a -> m) -> a -> m
    composOpMonoid :: (a -> m) -> a -> m
    composOpMonoid = m -> (m -> m -> m) -> (a -> m) -> a -> m
    forall a b. Uniplate a => b -> (b -> b -> b) -> (a -> b) -> a -> b
    composOpFold m
    forall a. Monoid a => a
    mempty m -> m -> m
    forall a. Monoid a => a -> a -> a
    mappend

    -- | @composOpMPlus = 'composOpFold' mzero mplus@
    composOpMPlus :: (Uniplate a, MonadPlus m) => (a -> m b) -> a -> m b
    composOpMPlus :: (a -> m b) -> a -> m b
    composOpMPlus = m b -> (m b -> m b -> m b) -> (a -> m b) -> a -> m b
    forall a b. Uniplate a => b -> (b -> b -> b) -> (a -> b) -> a -> b
    composOpFold m b
    forall (m :: * -> *) a. MonadPlus m => m a
    mzero m b -> m b -> m b
    forall (m :: * -> *) a. MonadPlus m => m a -> m a -> m a
    mplus

    -- | Probably replace with 'universe', perhaps 'para'
    composOpFold :: Uniplate a => b -> (b -> b -> b) -> (a -> b) -> a -> b
    composOpFold :: b -> (b -> b -> b) -> (a -> b) -> a -> b
    composOpFold zero :: b
    zero combine :: b -> b -> b
    combine f :: a -> b
    f = (b -> b -> b) -> b -> [b] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr b -> b -> b
    combine b
    zero ([b] -> b) -> (a -> [b]) -> a -> b
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (a -> b) -> [a] -> [b]
    forall a b. (a -> b) -> [a] -> [b]
    map a -> b
    f ([a] -> [b]) -> (a -> [a]) -> a -> [b]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . a -> [a]
    forall on. Uniplate on => on -> [on]
    children