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|
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{- |
Module : Text.Pandoc.Parsing.Future
Copyright : Copyright (C) 2006-2024 John MacFarlane
License : GPL-2.0-or-later
Maintainer : John MacFarlane <[email protected]>
Future type for parsing.
-}
module Text.Pandoc.Parsing.Future
( Future (..)
, runF
, askF
, asksF
, returnF
)
where
import Prelude hiding (Applicative(..))
import Control.Applicative (Applicative(..))
import Control.Monad.Reader
( asks, runReader, MonadReader(ask), Reader, ReaderT(ReaderT) )
-- | Reader monad wrapping the parser state. This is used to possibly
-- delay evaluation until all relevant information has been parsed and
-- made available in the parser state.
newtype Future s a = Future { runDelayed :: Reader s a }
deriving (Monad, Applicative, Functor)
instance Semigroup a => Semigroup (Future s a) where
(<>) = liftA2 (<>)
instance (Semigroup a, Monoid a) => Monoid (Future s a) where
mempty = return mempty
mappend = (<>)
-- | Run a delayed action with the given state.
runF :: Future s a -> s -> a
runF = runReader . runDelayed
askF :: Future s s
askF = Future ask
asksF :: (s -> a) -> Future s a
asksF f = Future $ asks f
returnF :: Monad m => a -> m (Future s a)
returnF = return . return
|
