Adding Next/Previous Post to Hakyll

So. The problem I was trying to solve in my last post was how to add next/prev links to a blogpost.
I’ve since figured out how to do that. See the commit.

My problem was, I had an Item String, and wanted to give a Compiler String corresponding to the next (or previous.. let’s ignore that for generality) post’s url.
I ran into difficulty by taking a list of Identifiers, and getting a list of Compiler Strings. That is, I loaded all the posts, and mapped them to their urls. (At which point I was stuck with [Compiler String]).
What I figured out to do was instead take the list of Identifiers, take the Identifier of the next post, and map that Identifier to a url. (Which is of type Compiler String).

If it’s unclear to you, then what I mean is that the problem I was struggling with was quite simple when done the wrong way.

When I struggled, I was wanting to get a Compiler [String] because I figured I would be able to look up the url after some url. I thought there would be some way to treat Compiler [String] more like [String].
Wrong idea, anyway.

Once you can go from Item a to Compiler String, then it’s quite easy to give this to a post.
For those who hadn’t tinkered around enough with Hakyll for this to be so obvious, you give the Item a -> Compiler String function to field "nextUrl", and adding this to the Context a given to the post.