add tags (per https://javran.github.io/posts/2014-03-01-add-tags-to-your-hakyll-blog.html)

site.hs

@@ -7,61 +7,80 @@ import           Hakyll
 --------------------------------------------------------------------------------
 main :: IO ()
 main = hakyll $ do
-    match "images/*" $ do
-        route   idRoute
-        compile copyFileCompiler
-
-    match "css/*" $ do
-        route   idRoute
-        compile compressCssCompiler
-
-    match (fromList ["about.rst", "contact.markdown"]) $ do
-        route   $ setExtension "html"
-        compile $ pandocCompiler
-            >>= loadAndApplyTemplate "templates/default.html" defaultContext
-            >>= relativizeUrls
-
-    match "posts/*" $ do
-        route $ setExtension "html"
-        compile $ pandocCompiler
-            >>= loadAndApplyTemplate "templates/post.html"    postCtx
-            >>= loadAndApplyTemplate "templates/default.html" postCtx
-            >>= relativizeUrls
-
-    create ["archive.html"] $ do
-        route idRoute
-        compile $ do
-            posts <- recentFirst =<< loadAll "posts/*"
-            let archiveCtx =
-                    listField "posts" postCtx (return posts) `mappend`
-                    constField "title" "Archives"            `mappend`
-                    defaultContext
-
-            makeItem ""
-                >>= loadAndApplyTemplate "templates/archive.html" archiveCtx
-                >>= loadAndApplyTemplate "templates/default.html" archiveCtx
-                >>= relativizeUrls
-
-
-    match "index.html" $ do
-        route idRoute
-        compile $ do
-            posts <- recentFirst =<< loadAll "posts/*"
-            let indexCtx =
-                    listField "posts" postCtx (return posts) `mappend`
-                    constField "title" "Home"                `mappend`
-                    defaultContext
-
-            getResourceBody
-                >>= applyAsTemplate indexCtx
-                >>= loadAndApplyTemplate "templates/default.html" indexCtx
-                >>= relativizeUrls
-
-    match "templates/*" $ compile templateBodyCompiler
+  match "images/*" $ do
+    route   idRoute
+    compile copyFileCompiler
+
+  match "css/*" $ do
+    route   idRoute
+    compile compressCssCompiler
+
+  match (fromList ["about.rst", "contact.markdown"]) $ do
+    route   $ setExtension "html"
+    compile $ pandocCompiler
+      >>= loadAndApplyTemplate "templates/default.html" defaultContext
+      >>= relativizeUrls
+
+  tags <- buildTags "posts/*" (fromCapture "tags/*.html")
+  tagsRules tags $ \tag pattern -> do
+    let title = "Posts tagged \"" ++ tag ++ "\""
+    route idRoute
+    compile $ do
+      posts <- recentFirst =<< loadAll pattern
+      let ctx = constField "title" title
+            `mappend` listField "posts" postCtx (return posts)
+            `mappend` defaultContext
+
+      makeItem ""
+        >>= loadAndApplyTemplate "templates/tag.html" ctx
+        >>= loadAndApplyTemplate "templates/default.html" ctx
+        >>= relativizeUrls
+
+  match "posts/*" $ do
+    route $ setExtension "html"
+    compile $ pandocCompiler
+      >>= loadAndApplyTemplate "templates/post.html"    postCtxWithTags
+      >>= loadAndApplyTemplate "templates/default.html" postCtxWithTags
+      >>= relativizeUrls
+
+  create ["archive.html"] $ do
+    route idRoute
+    compile $ do
+      posts <- recentFirst =<< loadAll "posts/*"
+      let archiveCtx =
+            listField "posts" postCtx (return posts) `mappend`
+            constField "title" "Archives"            `mappend`
+            defaultContext
+
+      makeItem ""
+        >>= loadAndApplyTemplate "templates/archive.html" archiveCtx
+        >>= loadAndApplyTemplate "templates/default.html" archiveCtx
+        >>= relativizeUrls
+
+
+  match "index.html" $ do
+    route idRoute
+    compile $ do
+      posts <- recentFirst =<< loadAll "posts/*"
+      let indexCtx =
+            listField "posts" postCtx (return posts) `mappend`
+            constField "title" "Home"                `mappend`
+            defaultContext
+
+      getResourceBody
+        >>= applyAsTemplate indexCtx
+        >>= loadAndApplyTemplate "templates/default.html" indexCtx
+        >>= relativizeUrls
+
+  match "templates/*" $ compile templateBodyCompiler
 
 
 --------------------------------------------------------------------------------
 postCtx :: Context String
 postCtx =
-    dateField "date" "%B %e, %Y" `mappend`
-    defaultContext
+  dateField "date" "%B %e, %Y" `mappend`
+  defaultContext
+
+postCtxWithTags :: Tags -> Context String
+postCtxWithTags tags = tagsField "tags" tags `mappend` postCtx
+

templates/post.html

@@ -1,8 +1,14 @@
 <div class="info">
-    Posted on $date$
-    $if(author)$
-        by $author$
-    $endif$
+  Posted on $date$
+  $if(author)$
+    by $author$
+  $endif$
+</div>
+
+<div class="info">
+  $if(tags)$
+  Tags: $tags$
+  $endif$
 </div>
 
 $body$