1 files changed, 21 insertions, 0 deletions
diff --git a/src/Text/Hakyll/Tags.hs b/src/Text/Hakyll/Tags.hs
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+++ b/src/Text/Hakyll/Tags.hs
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+-- | 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