3 files changed, 52 insertions, 45 deletions
diff --git a/src/Text/Hakyll/Internal/Template.hs b/src/Text/Hakyll/Internal/Template.hs
index 54636ee..bd9121b 100644
--- a/src/Text/Hakyll/Internal/Template.hs
+++ b/src/Text/Hakyll/Internal/Template.hs
@@ -22,16 +22,22 @@ import Text.Hakyll.Internal.Template.Template
 import Text.Hakyll.Internal.Template.Hamlet
 
 -- | Construct a @Template@ from a string.
+--
 fromString :: String -> Template
-fromString [] = End
-fromString string
-    | "$$" `isPrefixOf` string = EscapeCharacter (fromString $ tail tail')
-    | "$" `isPrefixOf` string = let (key, rest) = span isAlphaNum tail'
-                                in Identifier key (fromString rest)
-    | otherwise = let (chunk, rest) = break (== '$') string
-                  in Chunk chunk (fromString rest)
+fromString = Template . fromString'
   where
-    tail' = tail string
+    fromString' [] = []
+    fromString' string
+        | "$$" `isPrefixOf` string =
+            EscapeCharacter : (fromString' $ tail tail')
+        | "$" `isPrefixOf` string =
+            let (key, rest) = span isAlphaNum tail'
+            in Identifier key : fromString' rest
+        | otherwise =
+            let (chunk, rest) = break (== '$') string
+            in Chunk chunk : fromString' rest
+      where
+        tail' = tail string
 
 -- | Read a @Template@ from a file. This function might fetch the @Template@
 --   from the cache, if available.
@@ -60,15 +66,12 @@ readTemplate path = do
 --   "Context". When a key is not found, it is left as it is. You can specify
 --   the characters used to replace escaped dollars (@$$@) here.
 substitute :: String -> Template -> Context -> String 
-substitute escaper (Chunk chunk template) context =
-    chunk ++ substitute escaper template context
-substitute escaper (Identifier key template) context =
-    replacement ++ substitute escaper template context
+substitute escaper template context = substitute' =<< unTemplate template
   where
-    replacement = fromMaybe ('$' : key) $ M.lookup key $ unContext context
-substitute escaper (EscapeCharacter template) context =
-    escaper ++ substitute escaper template context
-substitute _ End _ = []
+    substitute' (Chunk chunk) = chunk
+    substitute' (Identifier key) =
+        fromMaybe ('$' : key) $ M.lookup key $ unContext context
+    substitute' (EscapeCharacter) = escaper
 
 -- | @substitute@ for use during a chain. This will leave escaped characters as
 --   they are.
diff --git a/src/Text/Hakyll/Internal/Template/Hamlet.hs b/src/Text/Hakyll/Internal/Template/Hamlet.hs
index 35c8e20..3bd9bb5 100644
--- a/src/Text/Hakyll/Internal/Template/Hamlet.hs
+++ b/src/Text/Hakyll/Internal/Template/Hamlet.hs
@@ -6,7 +6,6 @@ module Text.Hakyll.Internal.Template.Hamlet
     , fromHamletRT
     ) where
 
-import Data.List (intercalate)
 import Control.Monad.Trans (liftIO)
 import System.FilePath (takeExtension)
 
@@ -29,16 +28,18 @@ readHamletRT fileName = do
     string <- liftIO $ readFile fileName
     liftIO $ parseHamletRT settings string 
 
-
 -- | Convert a 'HamletRT' to a 'Template'
 --
 fromHamletRT :: HamletRT  -- ^ Hamlet runtime template
              -> Template  -- ^ Hakyll template
-fromHamletRT (HamletRT sd) = fromSimpleDoc sd
+fromHamletRT (HamletRT sd) = Template $ map fromSimpleDoc sd
   where
-    fromSimpleDoc :: [SimpleDoc] -> Template
-    fromSimpleDoc [] = End
-    fromSimpleDoc (SDRaw chunk : xs) = Chunk chunk $ fromSimpleDoc xs
-    fromSimpleDoc (SDVar vars : xs) =
-        Identifier (intercalate "." vars) $ fromSimpleDoc xs
-    fromSimpleDoc (_ : xs) = fromSimpleDoc xs  -- Unsupported elements
+    fromSimpleDoc :: SimpleDoc -> TemplateElement
+    fromSimpleDoc (SDRaw chunk) = Chunk chunk
+    fromSimpleDoc (SDVar [var]) = Identifier var
+    fromSimpleDoc (SDVar _) =
+        error "Hakyll does not support '.' in identifier names when using \
+              \hamlet templates."
+    fromSimpleDoc _ =
+        error "Only simple $key$ identifiers are allowed when using hamlet \
+              \templates."
diff --git a/src/Text/Hakyll/Internal/Template/Template.hs b/src/Text/Hakyll/Internal/Template/Template.hs
index 0fb2d09..49373fd 100644
--- a/src/Text/Hakyll/Internal/Template/Template.hs
+++ b/src/Text/Hakyll/Internal/Template/Template.hs
@@ -1,31 +1,34 @@
 -- | Module containing the template data structure.
 --
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 module Text.Hakyll.Internal.Template.Template
     ( Template (..)
+    , TemplateElement (..)
     ) where
 
-import Control.Monad (liftM, liftM2)
-import Data.Word (Word8)
+import Control.Applicative ((<$>))
 
-import Data.Binary (Binary, get, put, getWord8)
+import Data.Binary (Binary, get, getWord8, put, putWord8)
 
 -- | Datatype used for template substitutions.
 --
-data Template = Chunk String Template
-              | Identifier String Template
-              | EscapeCharacter Template
-              | End
-              deriving (Show, Read, Eq)
-    
-instance Binary Template where
-    put (Chunk string template) = put (0 :: Word8) >> put string >> put template
-    put (Identifier key template) = put (1 :: Word8) >> put key >> put template
-    put (EscapeCharacter template) = put (2 :: Word8) >> put template
-    put (End) = put (3 :: Word8)
+newtype Template = Template { unTemplate :: [TemplateElement] }
+                 deriving (Show, Eq, Binary)
 
-    get = do tag <- getWord8
-             case tag of 0 -> liftM2 Chunk get get
-                         1 -> liftM2 Identifier get get
-                         2 -> liftM EscapeCharacter get
-                         3 -> return End
-                         _ -> error "Error reading template"
+-- | Elements of a template.
+--
+data TemplateElement = Chunk String
+                     | Identifier String
+                     | EscapeCharacter
+                     deriving (Show, Eq)
+
+instance Binary TemplateElement where
+    put (Chunk string)    = putWord8 0 >> put string
+    put (Identifier key)  = putWord8 1 >> put key
+    put (EscapeCharacter) = putWord8 2
+
+    get = getWord8 >>= \tag ->
+         case tag of 0 -> Chunk <$> get
+                     1 -> Identifier <$> get
+                     2 -> return EscapeCharacter
+                     _ -> error "Error reading cached template"