My memory is hazy, so I cannot say for sure. The fact that I didn't document that as a requirement suggests that either I didn't know it was, or that I did, but it didn't help.
Either way I will revisit this now there is a new Debian stable, and I can install the package natively without using cabal.
That's probably the easiest way to get Haskell up and running. Then it's a simple matter of using cable to install other libraries, including Hakyll.