{-# LANGUAGE BlockArguments #-}

module WithLower where

-- base
import Data.Void

-- transformers
import Control.Monad.Trans.Reader

-- text
import Data.Text (Text)

-- megaparsec
import Text.Megaparsec

type Parser = Parsec Void Text

withLower :: ((forall a. ReaderT r f a -> f a) -> f b) -> ReaderT r f b
withLower k = ReaderT \r -> k (`runReaderT` r)

myParser :: ReaderT r Parser a
myParser = withLower \lower -> 
  choice [try (lower parserA) <|> try parserB <|> parserC]

parserA :: ReaderT r Parser a
parserA = undefined

parserB, parserC :: Parser a
parserB = undefined
parserC = undefined