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|
-- | 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
( RulesM
, Rules
, compile
, create
, route
, metaCompile
, metaCompileWith
) where
import Control.Applicative ((<$>))
import Control.Monad.Writer (tell)
import Control.Monad.Reader (ask)
import Control.Arrow (second, (>>>), arr, (>>^))
import Control.Monad.State (get, put)
import Data.Monoid (mempty)
import qualified Data.Set as S
import Data.Typeable (Typeable)
import Data.Binary (Binary)
import Hakyll.Core.ResourceProvider
import Hakyll.Core.Identifier
import Hakyll.Core.Identifier.Pattern
import Hakyll.Core.Compiler.Internal
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
--
tellRoute :: Routes -> Rules
tellRoute route' = RulesM $ tell $ RuleSet route' mempty mempty
-- | Add a number of compilers
--
tellCompilers :: (Binary a, Typeable a, Writable a)
=> [(Identifier, Compiler () a)]
-> Rules
tellCompilers compilers = RulesM $ tell $ RuleSet mempty compilers' mempty
where
compilers' = map (second boxCompiler) compilers
boxCompiler = (>>> arr compiledItem >>> arr CompileRule)
-- | Add resources
--
tellResources :: [Resource]
-> Rules
tellResources resources = RulesM $ tell $ RuleSet mempty mempty $ S.fromList resources
-- | Add a compilation rule to the rules.
--
-- This instructs all resources matching the given pattern to be compiled using
-- 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 Resource a -> Rules
compile pattern compiler = RulesM $ do
identifiers <- matches pattern . map unResource . resourceList <$> ask
unRulesM $ do
tellCompilers $ flip map identifiers $ \identifier ->
(identifier, constA (Resource identifier) >>> compiler)
tellResources $ map Resource identifiers
-- | Add a compilation rule
--
-- This sets a compiler for the given identifier. No resource is needed, since
-- we are creating the item from scratch. This is useful if you want to create a
-- page on your site that just takes content from other items -- but has no
-- actual content itself.
--
create :: (Binary a, Typeable a, Writable a)
=> Identifier -> Compiler () a -> Rules
create identifier compiler = tellCompilers [(identifier, compiler)]
-- | 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'
-- | 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.
--
-- This is needed when the list of compilers depends on something we cannot know
-- before actually running other compilers. The most typical example is if we
-- have a blogpost using tags.
--
-- Every post has a collection of tags. For example,
--
-- > post1: code, haskell
-- > post2: code, random
--
-- Now, we want to create a list of posts for every tag. We cannot write this
-- down in our 'Rules' DSL directly, since we don't know what tags the different
-- posts will have -- we depend on information that will only be available when
-- we are actually compiling the pages.
--
-- The solution is simple, using 'metaCompile', we can add a compiler that will
-- parse the pages and produce the compilers needed for the different tag pages.
--
-- 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)]
-- ^ Compiler generating the other compilers
-> Rules
-- ^ Resulting rules
metaCompile compiler = RulesM $ do
-- Create an identifier from the state
state <- get
let index = rulesMetaCompilerIndex state
id' = fromCaptureString "Hakyll.Core.Rules.metaCompile/*" (show index)
-- Update the state with a new identifier
put $ state {rulesMetaCompilerIndex = index + 1}
-- Fallback to 'metaCompileWith' with now known identifier
unRulesM $ metaCompileWith id' compiler
-- | Version of 'metaCompile' that allows you to specify a custom identifier for
-- the metacompiler.
--
metaCompileWith :: (Binary a, Typeable a, Writable a)
=> Identifier
-- ^ Identifier for this compiler
-> Compiler () [(Identifier, Compiler () a)]
-- ^ Compiler generating the other compilers
-> Rules
-- ^ Resulting rules
metaCompileWith identifier compiler = RulesM $ tell $
RuleSet mempty compilers mempty
where
makeRule = MetaCompileRule . map (second box)
compilers = [(identifier, compiler >>> arr makeRule )]
box = (>>> fromDependency identifier >>^ CompileRule . compiledItem)
|
