Added module to deal with tags.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/Text/Hakyll/Tags.hs b/src/Text/Hakyll/Tags.hs
new file mode 100644
index 0000000..98fda86
--- /dev/null
+++ b/src/Text/Hakyll/Tags.hs
@@ -0,0 +1,21 @@
+-- | Module containing some specialized functions to deal with tags.
+module Text.Hakyll.Tags
+    ( readTagMap
+    ) where
+
+import qualified Data.Map as M
+import qualified Data.ByteString.Lazy.Char8 as B
+import Control.Monad
+
+import Text.Hakyll.Util
+import Text.Hakyll.Page
+
+-- | Read a tag map. This creates a map from tags to page paths. This function
+--   assumes the tags are located in the `tags` metadata field, separated by
+--   commas.
+readTagMap :: [FilePath] -> IO (M.Map String [FilePath])
+readTagMap paths = foldM addPaths M.empty paths
+    where addPaths current path = do
+            page <- readPage path
+            let tags = map trim $ split "," $ B.unpack $ getValue ("tags") page
+            return $ foldr (\t -> M.insertWith (++) t [path]) current tags