From 93f29997a90474b740f624729029acf184906b35 Mon Sep 17 00:00:00 2001
From: Joey Hess <joey@kitenet.net>
Date: Sun, 2 Sep 2012 02:07:15 -0400
Subject: [PATCH] reduce some boilerplate using ghc extensions

---
 Assistant/WebApp/Types.hs | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/Assistant/WebApp/Types.hs b/Assistant/WebApp/Types.hs
index 988f909d74..26b73af9d2 100644
--- a/Assistant/WebApp/Types.hs
+++ b/Assistant/WebApp/Types.hs
@@ -5,7 +5,9 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
-{-# LANGUAGE TypeFamilies, QuasiQuotes, MultiParamTypeClasses, TemplateHaskell, OverloadedStrings, RankNTypes #-}
+{-# LANGUAGE FlexibleInstances, UndecidableInstances #-}
+{-# LANGUAGE TypeFamilies, QuasiQuotes, MultiParamTypeClasses #-}
+{-# LANGUAGE TemplateHaskell, OverloadedStrings, RankNTypes #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 
 module Assistant.WebApp.Types where
@@ -77,19 +79,7 @@ data SshData = SshData
 	}
 	deriving (Read, Show, Eq)
 
-instance PathPiece SshData where
-    toPathPiece = pack . show
-    fromPathPiece = readish . unpack
-
-
-instance PathPiece NotificationId where
-    toPathPiece = pack . show
-    fromPathPiece = readish . unpack
-
-instance PathPiece AlertId where
-    toPathPiece = pack . show
-    fromPathPiece = readish . unpack
-
-instance PathPiece Transfer where
+{- Allow any serializable data type to be used as a PathPiece -}
+instance (Show a, Read a) => PathPiece a where
     toPathPiece = pack . show
     fromPathPiece = readish . unpack