Draft posts with Hakyll

Posted on October 31, 2015

If you’d like to write a long posts in your Hakyll blog, you often can find that you’d like to commit a post (or several posts), but you’re are not going to deploy it on server. Here is my solution inspired by this post. Now I can call Hakyll with --with-drafts and it will use both posts and drafts directories to collect posts data.

There are several issues I had faced with when I was solving this problem:

  1. Detect what program is running in the draft mode.
  2. Pass posts to Hakyll.
  3. It is safer to have a separate folder for generated site while running in the draft mode to avoid the draft articles deploying by mistake.
  4. Hakyll itself uses cmdargs package which checks if the command is executed with proper options.

Passing posts to Hakyll

This is the easiest step. Hakyll uses pattern to match your blog posts to process them. By default it’s "posts/*". In many cases it is used in several places, so it’s a really good idea to define a variable. Patterns can be combined using .||. operator. So we can have something like:

main = do
  let postsPattern = if (draftMode)
    then "posts/*" .||. "drafts/*"
    else "posts/*"

  hakyll $ do
    match postsPattern $ do
      route $ setExtension "html"
      compile $ pandocCompiler
-- other routes implementation

Draft configuration

To put result into another directory we need to change configuration and pass it to Hakyll.

main = do
  let config = if (draftMode) draftConfiguration else defaultConfiguration

  hakyllWith config $ do
    match postsPattern $ do
-- routes implementation

-- Configuraiton for draft
draftConfiguration = defaultConfiguration {
        destinationDirectory = "_draftSite"
      , storeDirectory = "_draftCache"
      , tmpDirectory = "_draftCache/tmp"

Putting all together

So far so good, but we still haven’t detected if it’s a draft mode or not. We need to process command line arguments:

main = do
  draftMode <- fmap (elem "--with-drafts") getArgs

Unfortunately, this is not enough. As I mentioned before, cmdargs does not allow to pass unknown options, so we need to filter out all our stuff before passing it to Hakyll. The good news is that we can process arguments and replace them using withArgs function. So the final solution looks like that:

checkArgs :: [String] -> (Pattern, Configuration, [String])
checkArgs args = case partition (/= "--with-drafts") args of
    (_, []) -> ("posts/*",                  defaultConfiguration,   args)
    (as, _) -> ("posts/*" .||. "drafts/*",  draftConfiguration,     as)

main = checkArgs <$> getArgs >>= 
        \(postsPattern, conf, args) -> withArgs args $ hakyllWith conf $ do
    match postsPattern $ do
-- routes implementation

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