Add basic support for h-entry categories, which are actually more like tags than categories really

src/Handler/Categories.hs

@@ -0,0 +1,22 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE OverloadedStrings #-}
+module Handler.Categories where
+
+import Import hiding ( on, (==.) )
+
+import Database.Esqueleto
+import Web.Slug ( Slug, unSlug )
+import Widget.Feed ( hFeed )
+
+import qualified Data.Text as T
+
+getCategoryR :: Slug -> Handler Html
+getCategoryR tag = do
+    entries <- runDB . select . from $ \(category `InnerJoin` ec `InnerJoin` entry) -> do
+        on $ entry ^. EntryId ==. ec ^. EntryCategoryEntryId
+        on $ category ^. CategoryId ==. ec ^. EntryCategoryCategoryId
+        where_ $ category ^. CategoryTag ==. val tag
+        return entry
+    defaultLayout $ do
+        setTitle . toHtml . T.cons '#' . unSlug $ tag
+        hFeed entries