-- | This module provides means for reading and applying 'Template's. -- -- Templates are tools to convert items into a string. They are perfectly suited -- for laying out your site. -- -- Let's look at an example template: -- -- > <html> -- > <head> -- > <title>My crazy homepage - $title$</title> -- > </head> -- > <body> -- > <div id="header"> -- > <h1>My crazy homepage - $title$</h1> -- > </div> -- > <div id="content"> -- > $body$ -- > </div> -- > <div id="footer"> -- > By reading this you agree that I now own your soul -- > </div> -- > </body> -- > </html> -- -- As you can see, the format is very simple -- @$key$@ is used to render the -- @$key$@ field from the page, everything else is literally copied. If you want -- to literally insert @\"$key$\"@ into your page (for example, when you're -- writing a Hakyll tutorial) you can use -- -- > <p> -- > A literal $$key$$. -- > </p> -- -- Because of it's simplicity, these templates can be used for more than HTML: -- you could make, for example, CSS or JS templates as well. -- -- Apart from interpolating @$key$@s from the 'Context' you can also -- use the following macros: -- -- * @$if(key)$@ -- -- > $if(key)$ -- > <b> Defined </b> -- > $else$ -- > <b> Non-defined </b> -- > $endif$ -- -- This example will print @Defined@ if @key@ is defined in the -- context and @Non-defined@ otherwise. The @$else$@ clause is -- optional. -- -- * @$for(key)$@ -- -- The @for@ macro is used for enumerating 'Context' elements that are -- lists, i.e. constructed using the 'listField' function. Assume that -- in a context we have an element @listField \"key\" c itms@. Then -- the snippet -- -- > $for(key)$ -- > $x$ -- > $sep$, -- > $endfor$ -- -- would, for each item @i@ in 'itms', lookup @$x$@ in the context @c@ -- with item @i@, interpolate it, and join the resulting list with -- @,@. -- -- Another concrete example one may consider is the following. Given the -- context -- -- > listField "things" (field "thing" (return . itemBody)) -- > (sequence [makeItem "fruits", makeItem "vegetables"]) -- -- and a template -- -- > I like -- > $for(things)$ -- > fresh $thing$$sep$, and -- > $endfor$ -- -- the resulting page would look like -- -- > <p> -- > I like -- > -- > fresh fruits, and -- > -- > fresh vegetables -- > </p> -- -- The @$sep$@ part can be omitted. Usually, you can get by using the -- 'applyListTemplate' and 'applyJoinListTemplate' functions. -- -- * @$partial(path)$@ -- -- Loads a template located in a separate file and interpolates it -- under the current context. -- -- Assuming that the file @test.html@ contains -- -- > <b>$key$</b> -- -- The result of rendering -- -- > <p> -- > $partial("test.html")$ -- > </p> -- -- is the same as the result of rendering -- -- > <p> -- > <b>$key$</b> -- > </p> -- -- That is, calling @$partial$@ is equivalent to just copying and pasting -- template code. -- {-# LANGUAGE ScopedTypeVariables #-} module Hakyll.Web.Template ( Template , templateCompiler , applyTemplate , loadAndApplyTemplate , applyAsTemplate , readTemplate ) where -------------------------------------------------------------------------------- import Control.Monad (liftM) import Control.Monad.Error (MonadError (..)) import Data.List (intercalate) import Data.Monoid (mappend) import Prelude hiding (id) -------------------------------------------------------------------------------- import Hakyll.Core.Compiler import Hakyll.Core.Identifier import Hakyll.Core.Item import Hakyll.Web.Template.Context import Hakyll.Web.Template.Internal -------------------------------------------------------------------------------- -- | Read a template. templateCompiler :: Compiler (Item Template) templateCompiler = cached "Hakyll.Web.Template.templateCompiler" $ do item <- getResourceString return $ fmap readTemplate item -------------------------------------------------------------------------------- applyTemplate :: Template -- ^ Template -> Context a -- ^ Context -> Item a -- ^ Page -> Compiler (Item String) -- ^ Resulting item applyTemplate tpl context item = do body <- applyTemplate' tpl context item return $ itemSetBody body item -------------------------------------------------------------------------------- applyTemplate' :: forall a. Template -- ^ Template -> Context a -- ^ Context -> Item a -- ^ Page -> Compiler String -- ^ Resulting item applyTemplate' tpl context x = go tpl where context' :: String -> [String] -> Item a -> Compiler ContextField context' = unContext (context `mappend` missingField) go = liftM concat . mapM applyElem . unTemplate --------------------------------------------------------------------------- applyElem :: TemplateElement -> Compiler String applyElem (Chunk c) = return c applyElem (Expr e) = applyExpr e >>= getString e applyElem Escaped = return "$" applyElem (If e t mf) = (applyExpr e >> go t) `catchError` handler where handler _ = case mf of Nothing -> return "" Just f -> go f applyElem (For e b s) = applyExpr e >>= \cf -> case cf of StringField _ -> fail $ "Hakyll.Web.Template.applyTemplateWith: expected ListField but " ++ "got StringField for expr " ++ show e ListField c xs -> do sep <- maybe (return "") go s bs <- mapM (applyTemplate' b c) xs return $ intercalate sep bs applyElem (Partial e) = do p <- applyExpr e >>= getString e tpl' <- loadBody (fromFilePath p) applyTemplate' tpl' context x --------------------------------------------------------------------------- applyExpr :: TemplateExpr -> Compiler ContextField applyExpr (Ident (TemplateKey k)) = context' k [] x applyExpr (Call (TemplateKey k) args) = do args' <- mapM (\e -> applyExpr e >>= getString e) args context' k args' x applyExpr (StringLiteral s) = return (StringField s) ---------------------------------------------------------------------------- getString _ (StringField s) = return s getString e (ListField _ _) = fail $ "Hakyll.Web.Template.applyTemplateWith: expected StringField but " ++ "got ListField for expr " ++ show e -------------------------------------------------------------------------------- -- | The following pattern is so common: -- -- > tpl <- loadBody "templates/foo.html" -- > someCompiler -- > >>= applyTemplate tpl context -- -- That we have a single function which does this: -- -- > someCompiler -- > >>= loadAndApplyTemplate "templates/foo.html" context loadAndApplyTemplate :: Identifier -- ^ Template identifier -> Context a -- ^ Context -> Item a -- ^ Page -> Compiler (Item String) -- ^ Resulting item loadAndApplyTemplate identifier context item = do tpl <- loadBody identifier applyTemplate tpl context item -------------------------------------------------------------------------------- -- | It is also possible that you want to substitute @$key$@s within the body of -- an item. This function does that by interpreting the item body as a template, -- and then applying it to itself. applyAsTemplate :: Context String -- ^ Context -> Item String -- ^ Item and template -> Compiler (Item String) -- ^ Resulting item applyAsTemplate context item = let tpl = readTemplate $ itemBody item in applyTemplate tpl context item