From b20edfd96a9b62f5dadaba9772adb8abe0a3691d Mon Sep 17 00:00:00 2001
From: "Julian K. Arni" <jkarni@gmail.com>
Date: Wed, 16 Dec 2015 13:41:18 +0100
Subject: [PATCH] Fix loop in IsSubList

        See #293.
---
 servant/src/Servant/Utils/Links.hs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/servant/src/Servant/Utils/Links.hs b/servant/src/Servant/Utils/Links.hs
index b83d1178..b6bf7137 100644
--- a/servant/src/Servant/Utils/Links.hs
+++ b/servant/src/Servant/Utils/Links.hs
@@ -180,12 +180,13 @@ type family IsElem endpoint api :: Constraint where
     IsElem e e                              = ()
     IsElem e a                              = IsElem' e a
 
-
 type family IsSubList a b :: Constraint where
     IsSubList '[] b          = ()
-    IsSubList '[x] (x ': xs) = ()
-    IsSubList '[x] (y ': ys) = IsSubList '[x] ys
-    IsSubList (x ': xs) y    = IsSubList '[x] y `And` IsSubList xs y
+    IsSubList (x ': xs) y    = Elem x y `And` IsSubList xs y
+
+type family Elem e es :: Constraint where
+    Elem x (x ': xs) = ()
+    Elem y (x ': xs) = Elem y xs
 
 -- Phantom types for Param
 data Query