From 7af4014e3fb650db497249e113fe007a53ae6d09 Mon Sep 17 00:00:00 2001
From: Jasper Van der Jeugt <jaspervdj@gmail.com>
Date: Tue, 19 Jan 2010 09:53:52 +0100
Subject: [PATCH] [awesome feature] Added combining of Renderables.

---
 src/Text/Hakyll/Renderables.hs | 60 +++++++++++++++++++++++++++++-----
 1 file changed, 52 insertions(+), 8 deletions(-)

diff --git a/src/Text/Hakyll/Renderables.hs b/src/Text/Hakyll/Renderables.hs
index 0151f10..5832a09 100644
--- a/src/Text/Hakyll/Renderables.hs
+++ b/src/Text/Hakyll/Renderables.hs
@@ -3,6 +3,9 @@ module Text.Hakyll.Renderables
     , createCustomPage
     , PagePath
     , createPagePath
+    , CombinedRenderable
+    , combine
+    , combineWithURL
     ) where
 
 import qualified Data.Map as M
@@ -14,9 +17,9 @@ import Text.Hakyll.File
 
 -- | A custom page.
 data CustomPage = CustomPage 
-    { url :: String,
-      dependencies :: [FilePath],
-      mapping :: [(String, Either String (Hakyll String))]
+    { customPageURL :: String,
+      customPageDependencies :: [FilePath],
+      customPageContext :: [(String, Either String (Hakyll String))]
     }
 
 -- | Create a custom page.
@@ -33,12 +36,12 @@ createCustomPage :: String -- ^ Destination of the page, relative to _site.
 createCustomPage = CustomPage
 
 instance Renderable CustomPage where
-    getDependencies = dependencies
-    getURL = url
+    getDependencies = customPageDependencies
+    getURL = customPageURL
     toContext page = do
-        values <- mapM (either (return) (>>= return) . snd) (mapping page)
-        return $ M.fromList $ [ ("url", url page)
-                              ] ++ zip (map fst $ mapping page) values 
+        values <- mapM (either return id . snd) (customPageContext page)
+        return $ M.fromList $ [ ("url", customPageURL page)
+                              ] ++ zip (map fst $ customPageContext page) values
 
 -- | PagePath is a class that wraps a FilePath. This is used to render Pages
 --   without reading them first through use of caching.
@@ -53,3 +56,44 @@ instance Renderable PagePath where
     getDependencies (PagePath path) = return path
     getURL (PagePath path) = toURL path
     toContext (PagePath path) = readPage path >>= toContext
+
+-- | A combination of two other renderables.
+data CombinedRenderable a b = CombinedRenderable a b
+                            | CombinedRenderableWithURL FilePath a b
+
+-- | Combine two renderables. The url will always be taken from the first
+--   "Renderable". Also, if a `$key` is present in both renderables, the
+--   value from the first "Renderable" will be taken as well.
+combine :: (Renderable a, Renderable b) => a -> b -> CombinedRenderable a b
+combine = CombinedRenderable
+
+-- | Combine two renderables and set a custom URL.
+combineWithURL :: (Renderable a, Renderable b)
+               => FilePath
+               -> a
+               -> b
+               -> CombinedRenderable a b
+combineWithURL = CombinedRenderableWithURL
+
+-- | Render combinations.
+instance (Renderable a, Renderable b)
+         => Renderable (CombinedRenderable a b) where
+
+    -- Add the dependencies.
+    getDependencies (CombinedRenderable a b) =
+        getDependencies a ++ getDependencies b
+    getDependencies (CombinedRenderableWithURL _ a b) =
+        getDependencies a ++ getDependencies b
+
+    -- Take the url from the first renderable, or the specified URL.
+    getURL (CombinedRenderable a _) = getURL a
+    getURL (CombinedRenderableWithURL url _ _) = url
+
+    -- Take a union of the contexts.
+    toContext (CombinedRenderable a b) = do
+        c1 <- toContext a
+        c2 <- toContext b
+        return $ c1 `M.union` c2
+    toContext (CombinedRenderableWithURL url a b) = do
+        c <- toContext (CombinedRenderable a b)
+        return $ (M.singleton "url" url) `M.union` c