haskellhaskell-lucid

Run Reader wrapped in HtmlT, producing Html ()

I'm using Lucid to generate code for a static site, writing code in the HtmlT (Reader MyEnv) monad to transparently pass around some configuration stored in MyEnv.

The framework I'm using encapsulates the transformation from Html () to file output, so I'd like to write a function to transform HtmlT (Reader MyEnv) () to Html (); something like:

withEnv :: MyEnv -> HtmlT (Reader MyEnv) () -> Html ()

But I haven't yet come up with a simple way to implement this. Am I missing something fundamental, or is there a workaround?

Solution

  • You can use commuteHtmlT:

    commuteHtmlT :: HtmlT (Reader MyEnv) a -> Reader MyEnd (Html a)
runReader :: Reader a r -> a -> r

withEnv :: MyEnv -> HtmlT (Reader MyEnv) a -> Html a
withEnv e = ($ e) . runReader . commuteHtmlT