From e9b2fbab07b8f55ae6a9e120ab0b98c433842a8b Mon Sep 17 00:00:00 2001
From: Gracjan Polak <gracjan@scrive.com>
Date: Wed, 11 Sep 2013 13:29:22 +0300
Subject: [PATCH] Add a hack to support both Cabal-1.16 and Cabal-1.18 Setup.hs
 script (fixed number of arguments for programFindLocation)

---
 Setup.hs | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/Setup.hs b/Setup.hs
index 76d7605..7cbd484 100755
--- a/Setup.hs
+++ b/Setup.hs
@@ -1,4 +1,5 @@
 #!/usr/bin/env runhaskell
+{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
 
 import Distribution.Simple
 import Distribution.PackageDescription
@@ -26,8 +27,21 @@ main = defaultMainWithHooks simpleUserHooks {
     } 
 }
 
+-- 'ConstOrId' is a @Cabal-1.16@ vs @Cabal-1.18@ compatibility hack,
+-- 'programFindLocation' has a new (unused in this case)
+-- parameter. 'ConstOrId' adds this parameter when types say it is
+-- mandatory.
+class ConstOrId a b where
+    constOrId :: a -> b
+
+instance ConstOrId a a where
+    constOrId = id
+
+instance ConstOrId a (b -> a) where
+    constOrId = const
+
 pgconfigProgram = (simpleProgram "pgconfig or pg_config") {
-    programFindLocation = \verbosity -> do
+    programFindLocation = \verbosity -> constOrId $ do
       pgconfig  <- findProgramLocation verbosity "pgconfig"
       pg_config <- findProgramLocation verbosity "pg_config"
       return (pgconfig `mplus` pg_config)
-- 
1.8.4