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{-# LANGUAGE DeriveTraversable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{- |
Module : Text.Pandoc.Lua.Walk
Copyright : © 2012–2020 John MacFarlane,
© 2017-2020 Albert Krewinkel
License : GNU GPL, version 2 or above
Maintainer : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
Stability : alpha
Walking documents in a filter-suitable way.
-}
module Text.Pandoc.Lua.Walk
( SingletonsList (..)
)
where
import Control.Monad ((<=<))
import Text.Pandoc.Definition
import Text.Pandoc.Walk
-- | Helper type which allows to traverse trees in order, while splicing in
-- trees.
--
-- The only interesting use of this type is via it's '@Walkable@' instance. That
-- instance makes it possible to walk a Pandoc document (or a subset thereof),
-- while applying a function on each element of an AST element /list/, and have
-- the resulting list spliced back in place of the original element. This is the
-- traversal/splicing method used for Lua filters.
newtype SingletonsList a = SingletonsList { singletonsList :: [a] }
deriving (Functor, Foldable, Traversable)
--
-- SingletonsList Inline
--
instance {-# OVERLAPPING #-} Walkable (SingletonsList Inline) [Inline] where
walkM = walkSingletonsListM
query = querySingletonsList
instance Walkable (SingletonsList Inline) Pandoc where
walkM = walkPandocM
query = queryPandoc
instance Walkable (SingletonsList Inline) Citation where
walkM = walkCitationM
query = queryCitation
instance Walkable (SingletonsList Inline) Inline where
walkM = walkInlineM
query = queryInline
instance Walkable (SingletonsList Inline) Block where
walkM = walkBlockM
query = queryBlock
instance Walkable (SingletonsList Inline) MetaValue where
walkM = walkMetaValueM
query = queryMetaValue
instance Walkable (SingletonsList Inline) Meta where
walkM f (Meta metamap) = Meta <$> walkM f metamap
query f (Meta metamap) = query f metamap
--
-- SingletonsList Block
--
instance {-# OVERLAPPING #-} Walkable (SingletonsList Block) [Block] where
walkM = walkSingletonsListM
query = querySingletonsList
instance Walkable (SingletonsList Block) Pandoc where
walkM = walkPandocM
query = queryPandoc
instance Walkable (SingletonsList Block) Citation where
walkM = walkCitationM
query = queryCitation
instance Walkable (SingletonsList Block) Inline where
walkM = walkInlineM
query = queryInline
instance Walkable (SingletonsList Block) Block where
walkM = walkBlockM
query = queryBlock
instance Walkable (SingletonsList Block) MetaValue where
walkM = walkMetaValueM
query = queryMetaValue
instance Walkable (SingletonsList Block) Meta where
walkM f (Meta metamap) = Meta <$> walkM f metamap
query f (Meta metamap) = query f metamap
walkSingletonsListM :: (Monad m, Walkable (SingletonsList a) a)
=> (SingletonsList a -> m (SingletonsList a))
-> [a] -> m [a]
walkSingletonsListM f =
let f' = fmap singletonsList . f . SingletonsList . (:[]) <=< walkM f
in fmap mconcat . mapM f'
querySingletonsList :: (Monoid c, Walkable (SingletonsList a) a)
=> (SingletonsList a -> c)
-> [a] -> c
querySingletonsList f =
let f' x = f (SingletonsList [x]) `mappend` query f x
in mconcat . map f'
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