Add Resource type for improved type-safety

src/Hakyll/Core/Compiler.hs

@@ -87,7 +87,7 @@ getRouteFor = fromJob $ \identifier -> CompilerM $ do
 
 -- | Get the resource we are compiling as a string
 --
-getResourceString :: Compiler a String
+getResourceString :: Compiler Resource String
 getResourceString = getIdentifier >>> getResourceString'
   where
     getResourceString' = fromJob $ \id' -> CompilerM $ do
@@ -165,8 +165,8 @@ requireAllA pattern = (id &&& requireAll_ pattern >>>)
 
 cached :: (Binary a, Typeable a, Writable a)
        => String
-       -> Compiler () a
-       -> Compiler () a
+       -> Compiler Resource a
+       -> Compiler Resource a
 cached name (Compiler d j) = Compiler d $ const $ CompilerM $ do
     identifier <- compilerIdentifier <$> ask
     store <- compilerStore <$> ask
@@ -174,7 +174,7 @@ cached name (Compiler d j) = Compiler d $ const $ CompilerM $ do
     liftIO $ putStrLn $
         show identifier ++ ": " ++ if modified then "MODIFIED" else "OK"
     if modified
-        then do v <- unCompilerM $ j ()
+        then do v <- unCompilerM $ j Resource
                 liftIO $ storeSet store name identifier v
                 return v
         else do v <- liftIO $ storeGet store name identifier

src/Hakyll/Core/ResourceProvider.hs

@@ -3,7 +3,8 @@
 -- the concrete instance.
 --
 module Hakyll.Core.ResourceProvider
-    ( ResourceProvider (..)
+    ( Resource (..)
+    , ResourceProvider (..)
     , resourceExists
     , resourceDigest
     , resourceModified
@@ -19,6 +20,10 @@ import OpenSSL.Digest (MessageDigest (MD5))
 import Hakyll.Core.Identifier
 import Hakyll.Core.Store
 
+-- | A resource
+--
+data Resource = Resource
+
 -- | A value responsible for retrieving and listing resources
 --
 data ResourceProvider = ResourceProvider

src/Hakyll/Core/Rules.hs

@@ -39,6 +39,7 @@ import Hakyll.Core.Routes
 import Hakyll.Core.CompiledItem
 import Hakyll.Core.Writable
 import Hakyll.Core.Rules.Internal
+import Hakyll.Core.Util.Arrow
 
 -- | Add a route
 --
@@ -62,10 +63,11 @@ tellCompilers compilers = RulesM $ tell $ RuleSet mempty $
 -- happen. In this case, you might want to have a look at 'create'.
 --
 compile :: (Binary a, Typeable a, Writable a)
-        => Pattern -> Compiler () a -> Rules
+        => Pattern -> Compiler Resource a -> Rules
 compile pattern compiler = RulesM $ do
     identifiers <- matches pattern . resourceList <$> ask
-    unRulesM $ tellCompilers $ zip identifiers (repeat compiler)
+    unRulesM $ tellCompilers $ zip identifiers $ repeat $
+        constA Resource >>> compiler
 
 -- | Add a compilation rule
 --

src/Hakyll/Web.hs

@@ -19,6 +19,7 @@ import Text.Hamlet (HamletSettings)
 import Hakyll.Core.Compiler
 import Hakyll.Core.Writable
 import Hakyll.Core.Identifier
+import Hakyll.Core.ResourceProvider
 import Hakyll.Web.Page
 import Hakyll.Web.Pandoc
 import Hakyll.Web.Template
@@ -26,7 +27,7 @@ import Hakyll.Web.RelativizeUrls
 import Hakyll.Web.Util.String
 import Hakyll.Web.CompressCss
 
-defaultPageRead :: Compiler () (Page String)
+defaultPageRead :: Compiler Resource (Page String)
 defaultPageRead = cached "Hakyll.Web.defaultPageRead" $
     pageRead >>> addDefaultFields >>> arr applySelf >>> pageRenderPandoc
 
@@ -36,17 +37,17 @@ defaultRelativizeUrls = getRoute &&& id >>^ uncurry relativize
     relativize Nothing = id
     relativize (Just r) = fmap (relativizeUrls $ toSiteRoot r)
 
-defaultTemplateRead :: Compiler () Template
+defaultTemplateRead :: Compiler Resource Template
 defaultTemplateRead = cached "Hakyll.Web.defaultTemplateRead" $ templateRead
 
-defaultTemplateReadWith :: HamletSettings -> Compiler () Template
+defaultTemplateReadWith :: HamletSettings -> Compiler Resource Template
 defaultTemplateReadWith settings = cached "Hakyll.Web.defaultTemplateReadWith" $
     templateReadWith settings
 
-defaultCopyFile :: Compiler () CopyFile
+defaultCopyFile :: Compiler Resource CopyFile
 defaultCopyFile = getIdentifier >>^ CopyFile . toFilePath
 
-defaultCompressCss :: Compiler () String
+defaultCompressCss :: Compiler Resource String
 defaultCompressCss = getResourceString >>^ compressCss
 
 defaultApplyTemplate :: Identifier                            -- ^ Template

src/Hakyll/Web/Page.hs

@@ -68,6 +68,7 @@ import Data.Ord (comparing)
 
 import Hakyll.Core.Identifier
 import Hakyll.Core.Compiler
+import Hakyll.Core.ResourceProvider
 import Hakyll.Web.Page.Internal
 import Hakyll.Web.Page.Read
 import Hakyll.Web.Page.Metadata
@@ -90,7 +91,7 @@ toMap (Page m b) = M.insert "body" b m
 
 -- | Read a page (do not render it)
 --
-pageRead :: Compiler a (Page String)
+pageRead :: Compiler Resource (Page String)
 pageRead = getResourceString >>^ readPage
 
 -- | Add a number of default metadata fields to a page. These fields include:

src/Hakyll/Web/Template.hs

@@ -58,6 +58,7 @@ import Text.Hamlet (HamletSettings, defaultHamletSettings)
 
 import Hakyll.Core.Compiler
 import Hakyll.Core.Identifier
+import Hakyll.Core.ResourceProvider
 import Hakyll.Web.Template.Internal
 import Hakyll.Web.Template.Read
 import Hakyll.Web.Page
@@ -85,12 +86,12 @@ applySelf page = applyTemplate (readTemplate $ pageBody page) page
 -- @.hml@ or @.hamlet@, it will be considered as a Hamlet template, and parsed
 -- as such.
 --
-templateRead :: Compiler a Template
+templateRead :: Compiler Resource Template
 templateRead = templateReadWith defaultHamletSettings
 
 -- | Version of 'templateRead' that enables custom settings.
 --
-templateReadWith :: HamletSettings -> Compiler a Template
+templateReadWith :: HamletSettings -> Compiler Resource Template
 templateReadWith settings =
     getIdentifier &&& getResourceString >>^ uncurry read'
   where