1 files changed, 32 insertions, 0 deletions
diff --git a/lib/Hakyll/Core/Util/Parser.hs b/lib/Hakyll/Core/Util/Parser.hs
new file mode 100644
index 0000000..c4b2f8d
--- /dev/null
+++ b/lib/Hakyll/Core/Util/Parser.hs
@@ -0,0 +1,32 @@
+--------------------------------------------------------------------------------
+-- | Parser utilities
+module Hakyll.Core.Util.Parser
+    ( metadataKey
+    , reservedKeys
+    ) 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"]