Old Cabal Subhell

Sometimes I have a cabal that is too old for generating up-to-date boilerplate files for package installs, so I have to install a new cabal-install. But unfortunately I run into the same problem when installing the HTTP package, which is needed for cabal itself. So I am in a (pun totally intended, as you'll see later on) catch-22, and each time I feel being lost completely.

But there is a cure to this particular problem:

create a modified

mv dist/build/autogen/Paths_HTTP.hs dist/build

and patch it with

$ diff -u dist/build/autogen/Paths_HTTP.hs dist/build
--- dist/build/autogen/Paths_HTTP.hs 2013-02-27 20:07:01.437225000 +0100
+++ dist/build/Paths_HTTP.hs 2013-02-27 20:20:36.735526000 +0100
@@ -6,6 +6,7 @@

import Data.Version (Version(..))
import System.Environment (getEnv)
+import Control.Exception

version :: Version
version = Version {versionBranch = [4000,2,8], versionTags = []}
@@ -17,11 +18,14 @@
datadir = "/home/ggreif/share/HTTP-4000.2.8"
libexecdir = "/home/ggreif/libexec"

+hardCoded :: FilePath -> IOException -> IO FilePath
+hardCoded dir = const $ return dir
+
getBinDir, getLibDir, getDataDir, getLibexecDir :: IO FilePath
-getBinDir = catch (getEnv "HTTP_bindir") (\_ -> return bindir)
-getLibDir = catch (getEnv "HTTP_libdir") (\_ -> return libdir)
-getDataDir = catch (getEnv "HTTP_datadir") (\_ -> return datadir)
-getLibexecDir = catch (getEnv "HTTP_libexecdir") (\_ -> return libexecdir)
+getBinDir = catch (getEnv "HTTP_bindir") (hardCoded bindir)
+getLibDir = catch (getEnv "HTTP_libdir") (hardCoded libdir)
+getDataDir = catch (getEnv "HTTP_datadir") (hardCoded datadir)
+getLibexecDir = catch (getEnv "HTTP_libexecdir") (hardCoded libexecdir)

getDataFileName :: FilePath -> IO FilePath
getDataFileName name = do


This file is then preferably found by GHC and all is okay. Incidentally I already employed this trick in the past, but forgot about the details so I had to reinvent it again.

After escaping this particular subhell of cabal I came up with this blog post in order to not lose my way in the future. Hopefully it helps you too.