A Hakyll site file that provides for blog posts to link to "suggested" posts.

site-suggested-posts.hs

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{-# LANGUAGE OverloadedStrings #-}
import Data.Binary (Binary (..))
import Data.Monoid ((<>))
import System.Random.Shuffle (shuffle')
import System.Random.TF (newTFGen)
import Data.Typeable (Typeable (..))
import Hakyll


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main :: IO ()
main = hakyll $ do
    match "images/*" $ do
        route   idRoute
        compile copyFileCompiler

    match "css/*" $ do
        route   idRoute
        compile compressCssCompiler

    match (fromList ["about.rst", "contact.markdown"]) $ do
        route   $ setExtension "html"
        compile $ pandocCompiler
            >>= loadAndApplyTemplate "templates/default.html" defaultContext
            >>= relativizeUrls

    match "posts/*" $ do
        route $ setExtension "html"
        compile $ pandocCompiler
            >>= loadAndApplyTemplate "templates/post.html"    postCtx
            >>= saveSnapshot "content"
            >>= (\itm -> withSuggestedPosts 5 postCtx $ \ctx ->
                    return itm
                    >>= loadAndApplyTemplate "templates/default.html" ctx
                    >>= relativizeUrls)

    create ["archive.html"] $ do
        route idRoute
        compile $ do
            posts <- recentFirst =<< loadAll "posts/*"
            let archiveCtx =
                    listField "posts" postCtx (return posts) `mappend`
                    constField "title" "Archives"            `mappend`
                    defaultContext

            makeItem ""
                >>= loadAndApplyTemplate "templates/archive.html" archiveCtx
                >>= loadAndApplyTemplate "templates/default.html" archiveCtx
                >>= relativizeUrls


    match "index.html" $ do
        route idRoute
        compile $ do
            posts <- recentFirst =<< loadAll "posts/*"
            let indexCtx =
                    listField "posts" postCtx (return posts) `mappend`
                    constField "title" "Home"                `mappend`
                    defaultContext

            getResourceBody
                >>= applyAsTemplate indexCtx
                >>= loadAndApplyTemplate "templates/default.html" indexCtx
                >>= relativizeUrls

    match "templates/*" $ compile templateCompiler


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postCtx :: Context String
postCtx =
    dateField "date" "%B %e, %Y" `mappend`
    defaultContext

withSuggestedPosts :: (Binary a, Typeable a, Writable a)
                   => Int
                   -> Context String
                   -> (Context String -> Compiler (Item a))
                   -> Compiler (Item a)
withSuggestedPosts count ctx next = do
    ui <- getUnderlying
    rng <- unsafeCompiler newTFGen
    posts <- chronological =<< loadAllSnapshots ("posts/*" .&&. (complement . fromGlob . show $ ui)) "content"

    let postsSuggested = take (min count (length posts)) $ shuffle' posts (length posts) rng

        withSuggestedCtx =
          listField "suggestedPosts" postCtx (return postsSuggested)
          <> ctx

    next withSuggestedCtx