I was trying to follow along with a few different happstack tutorials and I found that I needed to cabal install a few things. Unfortunately when I did “cabal install happs-tutorial” I got the following:

Happstack/Helpers/DirBrowse.hs:88:105:
    Couldn't match expected type `String' against inferred type `Bool'
    In the third argument of `hscolour', namely `False'
    In the second argument of `(.)', namely
        `(hscolour defaultColourPrefs False False f)'
    In the first argument of `($)', namely
        `BrowseHtmlString . (hscolour defaultColourPrefs False False f)'
cabal: Error: some packages failed to install:
happs-tutorial-0.9.0 depends on happstack-helpers-0.30 which failed to
install.
happstack-helpers-0.30 failed during the building phase. The exception was:
exit: ExitFailure 1

It turns out that happstack-helpers is listed as dependening on hscolour >= 1.0 && < 2.0 when in reality it fails to compile against v1.15 of hscolour. I was thinking, damn, I'm going to have to manually download the sources for happstack-helpers, edit the cabal file so it has the right references and compile it manually. That's horribly convoluted for something that must happen all the time, there must be a better way!

I've been sitting on #haskell recently so I asked the question, and got some very speedy responses:

cabal install happs-tutorial --constraint="hscolor == 1.14"

That did the trick, and with a lot less effort!

I’ve asked quite a few questions on #haskell in the last few days and the response has been almost immediate every time and I’ve had my problem solved within minutes. Granted I’m still a Haskell newbie so my questions are probably trivial, but even still, it puts to shame the support I’ve received from a lot of commercial companies.

Hackage finally came back up, but I ran in to trouble with some guy called trhsx. Every time I tried to ‘cabal install happstack’ I got the following error:

Configuring hsp-0.4.5...
Preprocessing library hsp-0.4.5...
Building hsp-0.4.5...
ghc: could not execute: trhsx
cabal: Error: some packages failed to install:
happstack-0.3.2 depends on hsp-0.4.5 which failed to install.
hsp-0.4.5 failed during the building phase. The exception was:
exit: ExitFailure 1

After some digging I found out that I was supposed to have ~/.cabal/bin in my path, who would have thought? Anyway, I added the following to my .bashrc:

PATH=$PATH:~/.cabal/bin

…and happstack installed without a hitch.

Win!