[Haskell-beginners] Deploying a haskell application (not a webapp)

[Michael Orlitzky]

On 12/18/2014 03:20 AM, Alan Buxton wrote:
> Oh that's cool. Is there a way to configure this in some file so that when I
> build just this application a particular datadir is used?

The usual Setup.hs is just a dummy file; Cabal even ignores it. But if
you switch to a "custom" build (from "simple") you can do some
preprocessing in Setup.hs:

  https://www.haskell.org/cabal/users-guide/developing-packages.html

In the section "More complex packages", it shows you how to add hooks
that get executed before each configure/build/etc stage. If you add a
configure hook that mangles the datadir template, you can override the
default. Here's a Setup.hs that seems to work:

-- Welcome to the jungle, baby.
import Distribution.PackageDescription
import Distribution.Simple
import Distribution.Simple.Configure
import Distribution.Simple.InstallDirs
import Distribution.Simple.LocalBuildInfo
import Distribution.Simple.Setup

my_hooks :: UserHooks
my_hooks = simpleUserHooks { confHook = my_conf_hook }

main :: IO ()
main = defaultMainWithHooks my_hooks

my_conf_hook :: (GenericPackageDescription, HookedBuildInfo)
             -> ConfigFlags
             -> IO LocalBuildInfo
my_conf_hook (gpd,hbi) cf = do
  lbi <- configure (gpd, hbi) cf

  let orig_dirs = installDirTemplates lbi
  let my_datadir = toPathTemplate "/foo/bar"
  let my_dirs = orig_dirs { datadir = my_datadir }
  let my_lbi = lbi { installDirTemplates = my_dirs }
  return my_lbi