content: --------------------------------------------------------------------------------
  -- | Parser utilities
  module Hakyll.Core.Util.Parser
      ( metadataKey
      ) where
  
  
  --------------------------------------------------------------------------------
  import           Control.Applicative ((<|>))
  import           Control.Monad       (guard, mzero, void)
  import qualified Text.Parsec         as P
  import           Text.Parsec.String  (Parser)
  
  
  --------------------------------------------------------------------------------
  metadataKey :: Parser String
  metadataKey = do
      -- Ensure trailing '-' binds to '$' if present.
      let hyphon = P.try $ do
              void $ P.char '-'
              x <- P.lookAhead P.anyChar
              guard $ x /= '$'
              pure '-'
  
      i <- (:) <$> P.letter <*> P.many (P.alphaNum <|> P.oneOf "_." <|> hyphon)
      if i `elem` reservedKeys then mzero else return i
  
  
  --------------------------------------------------------------------------------
  reservedKeys :: [String]
  reservedKeys = ["if", "else", "endif", "for", "sep", "endfor", "partial"]
  