From dd81433d74579848e6853eb5a1500535c378c808 Mon Sep 17 00:00:00 2001
From: Jasper Van der Jeugt <jaspervdj@gmail.com>
Date: Fri, 11 Feb 2011 13:30:55 +0100
Subject: Split Rules module, add documentation

---
 src/Hakyll/Core/CompiledItem.hs   |   9 +++-
 src/Hakyll/Core/Compiler.hs       |   2 +-
 src/Hakyll/Core/Rules.hs          | 101 ++++++++++++++------------------------
 src/Hakyll/Core/Rules/Internal.hs |  70 ++++++++++++++++++++++++++
 src/Hakyll/Core/Run.hs            |   2 +-
 5 files changed, 117 insertions(+), 67 deletions(-)
 create mode 100644 src/Hakyll/Core/Rules/Internal.hs

(limited to 'src')

diff --git a/src/Hakyll/Core/CompiledItem.hs b/src/Hakyll/Core/CompiledItem.hs
index fe6730b..5dd0efc 100644
--- a/src/Hakyll/Core/CompiledItem.hs
+++ b/src/Hakyll/Core/CompiledItem.hs
@@ -1,6 +1,11 @@
 -- | A module containing a box datatype representing a compiled item. This
--- item can be of any type, given that a few restrictions hold (e.g. we want
--- a 'Typeable' instance to perform type-safe casts).
+-- item can be of any type, given that a few restrictions hold:
+--
+-- * we need a 'Typeable' instance to perform type-safe casts;
+--
+-- * we need a 'Binary' instance so we can serialize these items to the cache;
+--
+-- * we need a 'Writable' instance so the results can be saved.
 --
 {-# LANGUAGE ExistentialQuantification #-}
 module Hakyll.Core.CompiledItem
diff --git a/src/Hakyll/Core/Compiler.hs b/src/Hakyll/Core/Compiler.hs
index 5249478..85b912c 100644
--- a/src/Hakyll/Core/Compiler.hs
+++ b/src/Hakyll/Core/Compiler.hs
@@ -38,7 +38,7 @@ import Hakyll.Core.Writable
 import Hakyll.Core.ResourceProvider
 import Hakyll.Core.Compiler.Internal
 import Hakyll.Core.Store
-import Hakyll.Core.Rules
+import Hakyll.Core.Rules.Internal
 import Hakyll.Core.Routes
 
 -- | Run a compiler, yielding the resulting target and it's dependencies. This
diff --git a/src/Hakyll/Core/Rules.hs b/src/Hakyll/Core/Rules.hs
index 28aac1f..fbdd533 100644
--- a/src/Hakyll/Core/Rules.hs
+++ b/src/Hakyll/Core/Rules.hs
@@ -1,13 +1,19 @@
--- | This module provides a monadic DSL in which the user can specify the
--- different rules used to run the compilers
+-- | This module provides a declarative DSL in which the user can specify the
+-- different rules used to run the compilers.
+--
+-- The convention is to just list all items in the 'RulesM' monad, routes and
+-- compilation rules.
+--
+-- A typical usage example would be:
+--
+-- > main = hakyll $ do
+-- >     route   "posts/*" (setExtension "html")
+-- >     compile "posts/*" someCompiler
 --
 {-# LANGUAGE GeneralizedNewtypeDeriving, OverloadedStrings #-}
 module Hakyll.Core.Rules
-    ( CompileRule (..)
-    , RuleSet (..)
-    , RulesM
+    ( RulesM
     , Rules
-    , runRules
     , compile
     , create
     , route
@@ -15,12 +21,12 @@ module Hakyll.Core.Rules
     , metaCompileWith
     ) where
 
-import Control.Applicative (Applicative, (<$>))
-import Control.Monad.Writer (WriterT, execWriterT, tell)
-import Control.Monad.Reader (ReaderT, runReaderT, ask)
+import Control.Applicative ((<$>))
+import Control.Monad.Writer (tell)
+import Control.Monad.Reader (ask)
 import Control.Arrow (second, (>>>), arr, (>>^))
-import Control.Monad.State (State, evalState, get, put)
-import Data.Monoid (Monoid, mempty, mappend)
+import Control.Monad.State (get, put)
+import Data.Monoid (mempty)
 
 import Data.Typeable (Typeable)
 import Data.Binary (Binary)
@@ -32,53 +38,7 @@ import Hakyll.Core.Compiler.Internal
 import Hakyll.Core.Routes
 import Hakyll.Core.CompiledItem
 import Hakyll.Core.Writable
-
--- | Output of a compiler rule
---
--- * The compiler will produce a simple item. This is the most common case.
---
--- * The compiler will produce more compilers. These new compilers need to be
---   added to the runtime if possible, since other items might depend upon them.
---
-data CompileRule = CompileRule CompiledItem
-                 | MetaCompileRule [(Identifier, Compiler () CompileRule)]
-
--- | A collection of rules for the compilation process
---
-data RuleSet = RuleSet
-    { rulesRoutes    :: Routes
-    , rulesCompilers :: [(Identifier, Compiler () CompileRule)]
-    }
-
-instance Monoid RuleSet where
-    mempty = RuleSet mempty mempty
-    mappend (RuleSet r1 c1) (RuleSet r2 c2) =
-        RuleSet (mappend r1 r2) (mappend c1 c2)
-
--- | Rule state
---
-data RuleState = RuleState
-    { rulesMetaCompilerIndex :: Int
-    } deriving (Show)
-
--- | The monad used to compose rules
---
-newtype RulesM a = RulesM
-    { unRulesM :: ReaderT ResourceProvider (WriterT RuleSet (State RuleState)) a
-    } deriving (Monad, Functor, Applicative)
-
--- | Simplification of the RulesM type; usually, it will not return any
--- result.
---
-type Rules = RulesM ()
-
--- | Run a Rules monad, resulting in a 'RuleSet'
---
-runRules :: Rules -> ResourceProvider -> RuleSet
-runRules rules provider =
-    evalState (execWriterT $ runReaderT (unRulesM rules) provider) state
-  where
-    state = RuleState {rulesMetaCompilerIndex = 0}
+import Hakyll.Core.Rules.Internal
 
 -- | Add a route
 --
@@ -95,10 +55,11 @@ tellCompilers compilers = RulesM $ tell $ RuleSet mempty $
   where
     boxCompiler = (>>> arr compiledItem >>> arr CompileRule)
 
--- | Add a compilation rule
+-- | Add a compilation rule to the rules.
 --
 -- This instructs all resources matching the given pattern to be compiled using
--- the given compiler
+-- the given compiler. When no resources match the given pattern, nothing will
+-- happen. In this case, you might want to have a look at 'create'.
 --
 compile :: (Binary a, Typeable a, Writable a)
         => Pattern -> Compiler () a -> Rules
@@ -108,18 +69,32 @@ compile pattern compiler = RulesM $ do
 
 -- | Add a compilation rule
 --
--- This sets a compiler for the given identifier
+-- This sets a compiler for the given identifier. No resource is needed, since
+-- we are creating the item from scratch.
 --
 create :: (Binary a, Typeable a, Writable a)
        => Identifier -> Compiler () a -> Rules
 create identifier compiler = tellCompilers [(identifier, compiler)]
 
--- | Add a route
+-- | Add a route.
+--
+-- This adds a route for all items matching the given pattern.
 --
 route :: Pattern -> Routes -> Rules
 route pattern route' = tellRoute $ ifMatch pattern route'
 
--- | Add a compiler that produces other compilers over time
+-- | Apart from regular compilers, one is also able to specify metacompilers.
+-- Metacompilers are a special class of compilers: they are compilers which
+-- produce other compilers.
+--
+-- And indeed, we can see that the first argument to 'metaCompile' is a
+-- 'Compiler' which produces a list of ('Identifier', 'Compiler') pairs. The
+-- idea is simple: 'metaCompile' produces a list of compilers, and the
+-- corresponding identifiers.
+--
+-- For simple hakyll systems, it is no need for this construction. More
+-- formally, it is only needed when the content of one or more items determines
+-- which items must be rendered.
 --
 metaCompile :: (Binary a, Typeable a, Writable a)
             => Compiler () [(Identifier, Compiler () a)]   
diff --git a/src/Hakyll/Core/Rules/Internal.hs b/src/Hakyll/Core/Rules/Internal.hs
new file mode 100644
index 0000000..bedc67a
--- /dev/null
+++ b/src/Hakyll/Core/Rules/Internal.hs
@@ -0,0 +1,70 @@
+-- | Internal rules module for types which are not exposed to the user
+--
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module Hakyll.Core.Rules.Internal
+    ( CompileRule (..)
+    , RuleSet (..)
+    , RuleState (..)
+    , RulesM (..)
+    , Rules
+    , runRules
+    ) where
+
+import Control.Applicative (Applicative)
+import Control.Monad.Writer (WriterT, execWriterT)
+import Control.Monad.Reader (ReaderT, runReaderT)
+import Control.Monad.State (State, evalState)
+import Data.Monoid (Monoid, mempty, mappend)
+
+import Hakyll.Core.ResourceProvider
+import Hakyll.Core.Identifier
+import Hakyll.Core.Compiler.Internal
+import Hakyll.Core.Routes
+import Hakyll.Core.CompiledItem
+
+-- | Output of a compiler rule
+--
+-- * The compiler will produce a simple item. This is the most common case.
+--
+-- * The compiler will produce more compilers. These new compilers need to be
+--   added to the runtime if possible, since other items might depend upon them.
+--
+data CompileRule = CompileRule CompiledItem
+                 | MetaCompileRule [(Identifier, Compiler () CompileRule)]
+
+-- | A collection of rules for the compilation process
+--
+data RuleSet = RuleSet
+    { rulesRoutes    :: Routes
+    , rulesCompilers :: [(Identifier, Compiler () CompileRule)]
+    }
+
+instance Monoid RuleSet where
+    mempty = RuleSet mempty mempty
+    mappend (RuleSet r1 c1) (RuleSet r2 c2) =
+        RuleSet (mappend r1 r2) (mappend c1 c2)
+
+-- | Rule state
+--
+data RuleState = RuleState
+    { rulesMetaCompilerIndex :: Int
+    } deriving (Show)
+
+-- | The monad used to compose rules
+--
+newtype RulesM a = RulesM
+    { unRulesM :: ReaderT ResourceProvider (WriterT RuleSet (State RuleState)) a
+    } deriving (Monad, Functor, Applicative)
+
+-- | Simplification of the RulesM type; usually, it will not return any
+-- result.
+--
+type Rules = RulesM ()
+
+-- | Run a Rules monad, resulting in a 'RuleSet'
+--
+runRules :: Rules -> ResourceProvider -> RuleSet
+runRules rules provider =
+    evalState (execWriterT $ runReaderT (unRulesM rules) provider) state
+  where
+    state = RuleState {rulesMetaCompilerIndex = 0}
diff --git a/src/Hakyll/Core/Run.hs b/src/Hakyll/Core/Run.hs
index de4114c..7e6851f 100644
--- a/src/Hakyll/Core/Run.hs
+++ b/src/Hakyll/Core/Run.hs
@@ -25,7 +25,7 @@ import Hakyll.Core.Compiler
 import Hakyll.Core.Compiler.Internal
 import Hakyll.Core.ResourceProvider
 import Hakyll.Core.ResourceProvider.FileResourceProvider
-import Hakyll.Core.Rules
+import Hakyll.Core.Rules.Internal
 import Hakyll.Core.DirectedGraph
 import Hakyll.Core.DirectedGraph.DependencySolver
 import Hakyll.Core.Writable
-- 
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