    -- | Generalized cursors to be applied to different nodes.
    module Text.XML.Cursor.Generic
        ( -- * Core
          Cursor
        , Axis
        , toCursor
        , node
          -- * Axes
        , child
        , parent
        , precedingSibling
        , followingSibling
        , ancestor
        , descendant
        , orSelf
        , preceding
        , following
          -- * Operators
        , (&|)
        , (&/)
        , (&//)
        , (&.//)
        , ($|)
        , ($/)
        , ($//)
        , ($.//)
        , (>=>)
        ) where

    import Data.Maybe (maybeToList)
    import Data.List (foldl')
    import Control.Monad ((>=>))

    type DiffCursor node = [Cursor node] -> [Cursor node]
    type Axis node = Cursor node -> [Cursor node]

    -- | A cursor: contains an XML 'Node' and pointers to its children, ancestors and siblings.
    data Cursor node = Cursor
        { forall node. Cursor node -> Maybe (Cursor node)
    parent' :: Maybe (Cursor node)
        , forall node. Cursor node -> DiffCursor node
    precedingSibling' :: DiffCursor node
        , forall node. Cursor node -> DiffCursor node
    followingSibling' :: DiffCursor node
        -- | The child axis. XPath:
        -- /the child axis contains the children of the context node/.
        , forall node. Cursor node -> [Cursor node]
    child :: [Cursor node]
        -- | The current node.
        , forall node. Cursor node -> node
    node :: node
        }

    instance Show node => Show (Cursor node) where
        show :: Cursor node -> String
    show Cursor { node :: forall node. Cursor node -> node
    node = node
    n } = String
    "Cursor @ " String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ node -> String
    forall a. Show a => a -> String
    show node
    n

    toCursor :: (node -> [node]) -- ^ get children
             -> node
             -> Cursor node
    toCursor :: forall node. (node -> [node]) -> node -> Cursor node
    toCursor node -> [node]
    cs = (node -> [node])
    -> Maybe (Cursor node)
    -> DiffCursor node
    -> DiffCursor node
    -> node
    -> Cursor node
    forall node.
    (node -> [node])
    -> Maybe (Cursor node)
    -> DiffCursor node
    -> DiffCursor node
    -> node
    -> Cursor node
    toCursor' node -> [node]
    cs Maybe (Cursor node)
    forall a. Maybe a
    Nothing DiffCursor node
    forall a. a -> a
    id DiffCursor node
    forall a. a -> a
    id

    toCursor' :: (node -> [node])
              -> Maybe (Cursor node) -> DiffCursor node -> DiffCursor node -> node -> Cursor node
    toCursor' :: forall node.
    (node -> [node])
    -> Maybe (Cursor node)
    -> DiffCursor node
    -> DiffCursor node
    -> node
    -> Cursor node
    toCursor' node -> [node]
    cs Maybe (Cursor node)
    par DiffCursor node
    pre DiffCursor node
    fol node
    n =
        Cursor node
    me
      where
        me :: Cursor node
    me = Maybe (Cursor node)
    -> DiffCursor node
    -> DiffCursor node
    -> [Cursor node]
    -> node
    -> Cursor node
    forall node.
    Maybe (Cursor node)
    -> DiffCursor node
    -> DiffCursor node
    -> [Cursor node]
    -> node
    -> Cursor node
    Cursor Maybe (Cursor node)
    par DiffCursor node
    pre DiffCursor node
    fol [Cursor node]
    chi node
    n
        chi' :: [node]
    chi' = node -> [node]
    cs node
    n
        chi :: [Cursor node]
    chi = DiffCursor node -> [node] -> DiffCursor node
    go DiffCursor node
    forall a. a -> a
    id [node]
    chi' []
        go :: DiffCursor node -> [node] -> DiffCursor node
    go DiffCursor node
    _ [] = DiffCursor node
    forall a. a -> a
    id
        go DiffCursor node
    pre' (node
    n':[node]
    ns') =
            (:) Cursor node
    me' DiffCursor node -> DiffCursor node -> DiffCursor node
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DiffCursor node
    fol'
          where
            me' :: Cursor node
    me' = (node -> [node])
    -> Maybe (Cursor node)
    -> DiffCursor node
    -> DiffCursor node
    -> node
    -> Cursor node
    forall node.
    (node -> [node])
    -> Maybe (Cursor node)
    -> DiffCursor node
    -> DiffCursor node
    -> node
    -> Cursor node
    toCursor' node -> [node]
    cs (Cursor node -> Maybe (Cursor node)
    forall a. a -> Maybe a
    Just Cursor node
    me) DiffCursor node
    pre' DiffCursor node
    fol' node
    n'
            fol' :: DiffCursor node
    fol' = DiffCursor node -> [node] -> DiffCursor node
    go (DiffCursor node
    pre' DiffCursor node -> DiffCursor node -> DiffCursor node
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (:) Cursor node
    me') [node]
    ns'

    -- | The parent axis. As described in XPath:
    -- /the parent axis contains the parent of the context node, if there is one/.
    --
    -- Every node but the root element of the document has a parent. Parent nodes
    -- will always be 'NodeElement's.
    parent :: Axis node
    parent :: forall node. Cursor node -> [Cursor node]
    parent = Maybe (Cursor node) -> [Cursor node]
    forall a. Maybe a -> [a]
    maybeToList (Maybe (Cursor node) -> [Cursor node])
    -> (Cursor node -> Maybe (Cursor node))
    -> Cursor node
    -> [Cursor node]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Cursor node -> Maybe (Cursor node)
    forall node. Cursor node -> Maybe (Cursor node)
    parent'

    -- | The preceding-sibling axis. XPath:
    -- /the preceding-sibling axis contains all the preceding siblings of the context node [...]/.
    precedingSibling :: Axis node
    precedingSibling :: forall node. Cursor node -> [Cursor node]
    precedingSibling = (([Cursor node] -> [Cursor node]) -> [Cursor node] -> [Cursor node]
    forall a b. (a -> b) -> a -> b
    $ []) (([Cursor node] -> [Cursor node]) -> [Cursor node])
    -> (Cursor node -> [Cursor node] -> [Cursor node])
    -> Cursor node
    -> [Cursor node]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Cursor node -> [Cursor node] -> [Cursor node]
    forall node. Cursor node -> DiffCursor node
    precedingSibling'

    -- | The following-sibling axis. XPath:
    -- /the following-sibling axis contains all the following siblings of the context node [...]/.
    followingSibling :: Axis node
    followingSibling :: forall node. Cursor node -> [Cursor node]
    followingSibling = (([Cursor node] -> [Cursor node]) -> [Cursor node] -> [Cursor node]
    forall a b. (a -> b) -> a -> b
    $ []) (([Cursor node] -> [Cursor node]) -> [Cursor node])
    -> (Cursor node -> [Cursor node] -> [Cursor node])
    -> Cursor node
    -> [Cursor node]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Cursor node -> [Cursor node] -> [Cursor node]
    forall node. Cursor node -> DiffCursor node
    followingSibling'

    -- | The preceding axis. XPath:
    -- /the preceding axis contains all nodes in the same document as the context node that are before the context node in document order, excluding any ancestors and excluding attribute nodes and namespace nodes/.
    preceding :: Axis node
    preceding :: forall node. Cursor node -> [Cursor node]
    preceding Cursor node
    c =
        [Cursor node] -> [Cursor node] -> [Cursor node]
    forall {t :: * -> *} {node}.
    Foldable t =>
    t (Cursor node) -> [Cursor node] -> [Cursor node]
    go (Cursor node -> [Cursor node] -> [Cursor node]
    forall node. Cursor node -> DiffCursor node
    precedingSibling' Cursor node
    c []) (Axis node
    forall node. Cursor node -> [Cursor node]
    parent Cursor node
    c [Cursor node] -> Axis node -> [Cursor node]
    forall a b. [a] -> (a -> [b]) -> [b]
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= Axis node
    forall node. Cursor node -> [Cursor node]
    preceding)
      where
        go :: t (Cursor node) -> [Cursor node] -> [Cursor node]
    go t (Cursor node)
    x [Cursor node]
    y = ([Cursor node] -> Cursor node -> [Cursor node])
    -> [Cursor node] -> t (Cursor node) -> [Cursor node]
    forall b a. (b -> a -> b) -> b -> t a -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' ((Cursor node -> [Cursor node] -> [Cursor node])
    -> [Cursor node] -> Cursor node -> [Cursor node]
    forall a b c. (a -> b -> c) -> b -> a -> c
    flip Cursor node -> [Cursor node] -> [Cursor node]
    forall node. Cursor node -> DiffCursor node
    go') [Cursor node]
    y t (Cursor node)
    x
        go' :: Cursor node -> [Cursor node] -> [Cursor node]
    go' Cursor node
    x [Cursor node]
    rest = ([Cursor node] -> Cursor node -> [Cursor node])
    -> [Cursor node] -> [Cursor node] -> [Cursor node]
    forall b a. (b -> a -> b) -> b -> [a] -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' ((Cursor node -> [Cursor node] -> [Cursor node])
    -> [Cursor node] -> Cursor node -> [Cursor node]
    forall a b c. (a -> b -> c) -> b -> a -> c
    flip  Cursor node -> [Cursor node] -> [Cursor node]
    go') (Cursor node
    x Cursor node -> [Cursor node] -> [Cursor node]
    forall a. a -> [a] -> [a]
    : [Cursor node]
    rest) (Cursor node -> [Cursor node]
    forall node. Cursor node -> [Cursor node]
    child Cursor node
    x)

    -- | The following axis. XPath:
    -- /the following axis contains all nodes in the same document as the context node that are after the context node in document order, excluding any descendants and excluding attribute nodes and namespace nodes/.
    following :: Axis node
    following :: forall node. Cursor node -> [Cursor node]
    following Cursor node
    c =
        ([Cursor node] -> [Cursor node]) -> [Cursor node] -> [Cursor node]
    forall {t :: * -> *} {a} {node}.
    Foldable t =>
    ([a] -> t (Cursor node)) -> [Cursor node] -> [Cursor node]
    go (Cursor node -> [Cursor node] -> [Cursor node]
    forall node. Cursor node -> DiffCursor node
    followingSibling' Cursor node
    c) (Axis node
    forall node. Cursor node -> [Cursor node]
    parent Cursor node
    c [Cursor node] -> Axis node -> [Cursor node]
    forall a b. [a] -> (a -> [b]) -> [b]
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= Axis node
    forall node. Cursor node -> [Cursor node]
    following)
      where
        go :: ([a] -> t (Cursor node)) -> [Cursor node] -> [Cursor node]
    go [a] -> t (Cursor node)
    x [Cursor node]
    z = (Cursor node -> [Cursor node] -> [Cursor node])
    -> [Cursor node] -> t (Cursor node) -> [Cursor node]
    forall a b. (a -> b -> b) -> b -> t a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr Cursor node -> [Cursor node] -> [Cursor node]
    forall node. Cursor node -> DiffCursor node
    go' [Cursor node]
    z ([a] -> t (Cursor node)
    x [])
        go' :: Cursor node -> [Cursor node] -> [Cursor node]
    go' Cursor node
    x [Cursor node]
    rest = Cursor node
    x Cursor node -> [Cursor node] -> [Cursor node]
    forall a. a -> [a] -> [a]
    : (Cursor node -> [Cursor node] -> [Cursor node])
    -> [Cursor node] -> [Cursor node] -> [Cursor node]
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr Cursor node -> [Cursor node] -> [Cursor node]
    go' [Cursor node]
    rest (Cursor node -> [Cursor node]
    forall node. Cursor node -> [Cursor node]
    child Cursor node
    x)

    -- | The ancestor axis. XPath:
    -- /the ancestor axis contains the ancestors of the context node; the ancestors of the context node consist of the parent of context node and the parent's parent and so on; thus, the ancestor axis will always include the root node, unless the context node is the root node/.
    ancestor :: Axis node
    ancestor :: forall node. Cursor node -> [Cursor node]
    ancestor = Axis node
    forall node. Cursor node -> [Cursor node]
    parent Axis node -> Axis node -> Axis node
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> (\Cursor node
    p -> Cursor node
    p Cursor node -> [Cursor node] -> [Cursor node]
    forall a. a -> [a] -> [a]
    : Axis node
    forall node. Cursor node -> [Cursor node]
    ancestor Cursor node
    p)

    -- | The descendant axis. XPath:
    -- /the descendant axis contains the descendants of the context node; a descendant is a child or a child of a child and so on; thus the descendant axis never contains attribute or namespace nodes/.
    descendant :: Axis node
    descendant :: forall node. Cursor node -> [Cursor node]
    descendant = Cursor node -> [Cursor node]
    forall node. Cursor node -> [Cursor node]
    child (Cursor node -> [Cursor node])
    -> (Cursor node -> [Cursor node]) -> Cursor node -> [Cursor node]
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> (\Cursor node
    c -> Cursor node
    c Cursor node -> [Cursor node] -> [Cursor node]
    forall a. a -> [a] -> [a]
    : Cursor node -> [Cursor node]
    forall node. Cursor node -> [Cursor node]
    descendant Cursor node
    c)

    -- | Modify an axis by adding the context node itself as the first element of the result list.
    orSelf :: Axis node -> Axis node
    orSelf :: forall node. Axis node -> Axis node
    orSelf Axis node
    ax Cursor node
    c = Cursor node
    c Cursor node -> [Cursor node] -> [Cursor node]
    forall a. a -> [a] -> [a]
    : Axis node
    ax Cursor node
    c

    infixr 1 &|
    infixr 1 &/
    infixr 1 &//
    infixr 1 &.//
    infixr 1 $|
    infixr 1 $/
    infixr 1 $//
    infixr 1 $.//

    -- | Apply a function to the result of an axis.
    (&|) :: (Cursor node -> [a]) -> (a -> b) -> (Cursor node -> [b])
    Cursor node -> [a]
    f &| :: forall node a b.
    (Cursor node -> [a]) -> (a -> b) -> Cursor node -> [b]
    &| a -> b
    g = (a -> b) -> [a] -> [b]
    forall a b. (a -> b) -> [a] -> [b]
    map a -> b
    g ([a] -> [b]) -> (Cursor node -> [a]) -> Cursor node -> [b]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Cursor node -> [a]
    f

    -- | Combine two axes so that the second works on the children of the results
    -- of the first.
    (&/) :: Axis node -> (Cursor node -> [a]) -> (Cursor node -> [a])
    Axis node
    f &/ :: forall node a.
    Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    &/ Cursor node -> [a]
    g = Axis node
    f Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> Axis node
    forall node. Cursor node -> [Cursor node]
    child Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> Cursor node -> [a]
    g

    -- | Combine two axes so that the second works on the descendants of the results
    -- of the first.
    (&//) :: Axis node -> (Cursor node -> [a]) -> (Cursor node -> [a])
    Axis node
    f &// :: forall node a.
    Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    &// Cursor node -> [a]
    g = Axis node
    f Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> Axis node
    forall node. Cursor node -> [Cursor node]
    descendant Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> Cursor node -> [a]
    g

    -- | Combine two axes so that the second works on both the result nodes, and their
    -- descendants.
    (&.//) :: Axis node -> (Cursor node -> [a]) -> (Cursor node -> [a])
    Axis node
    f &.// :: forall node a.
    Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    &.// Cursor node -> [a]
    g = Axis node
    f Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> Axis node -> Axis node
    forall node. Axis node -> Axis node
    orSelf Axis node
    forall node. Cursor node -> [Cursor node]
    descendant Axis node -> (Cursor node -> [a]) -> Cursor node -> [a]
    forall (m :: * -> *) a b c.
    Monad m =>
    (a -> m b) -> (b -> m c) -> a -> m c
    >=> Cursor node -> [a]
    g

    -- | Apply an axis to a 'Cursor node'.
    ($|) :: Cursor node -> (Cursor node -> a) -> a
    Cursor node
    v $| :: forall node a. Cursor node -> (Cursor node -> a) -> a
    $| Cursor node -> a
    f = Cursor node -> a
    f Cursor node
    v

    -- | Apply an axis to the children of a 'Cursor node'.
    ($/) :: Cursor node -> (Cursor node -> [a]) -> [a]
    Cursor node
    v $/ :: forall node a. Cursor node -> (Cursor node -> [a]) -> [a]
    $/ Cursor node -> [a]
    f = Cursor node -> [Cursor node]
    forall node. Cursor node -> [Cursor node]
    child Cursor node
    v [Cursor node] -> (Cursor node -> [a]) -> [a]
    forall a b. [a] -> (a -> [b]) -> [b]
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= Cursor node -> [a]
    f

    -- | Apply an axis to the descendants of a 'Cursor node'.
    ($//) :: Cursor node -> (Cursor node -> [a]) -> [a]
    Cursor node
    v $// :: forall node a. Cursor node -> (Cursor node -> [a]) -> [a]
    $// Cursor node -> [a]
    f = Axis node
    forall node. Cursor node -> [Cursor node]
    descendant Cursor node
    v [Cursor node] -> (Cursor node -> [a]) -> [a]
    forall a b. [a] -> (a -> [b]) -> [b]
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= Cursor node -> [a]
    f

    -- | Apply an axis to a 'Cursor node' as well as its descendants.
    ($.//) :: Cursor node -> (Cursor node -> [a]) -> [a]
    Cursor node
    v $.// :: forall node a. Cursor node -> (Cursor node -> [a]) -> [a]
    $.// Cursor node -> [a]
    f = Axis node -> Axis node
    forall node. Axis node -> Axis node
    orSelf Axis node
    forall node. Cursor node -> [Cursor node]
    descendant Cursor node
    v [Cursor node] -> (Cursor node -> [a]) -> [a]
    forall a b. [a] -> (a -> [b]) -> [b]
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= Cursor node -> [a]
    f