From b15369baae12c38cfb76c75bb74fbbee8b0da735 Mon Sep 17 00:00:00 2001
From: Nathaniel Wesley Filardo <nwf@cs.jhu.edu>
Date: Thu, 29 Nov 2012 02:10:58 -0500
Subject: [PATCH] Add hrllen to HList utilities module

---
 src/Dyna/XXX/HList.hs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/Dyna/XXX/HList.hs b/src/Dyna/XXX/HList.hs
index 8eecd93..83bc6e2 100644
--- a/src/Dyna/XXX/HList.hs
+++ b/src/Dyna/XXX/HList.hs
@@ -25,7 +25,7 @@ module Dyna.XXX.HList(
   HList(..), hlmapa,
 
   -- * HLists of a type constructor's images
-  HRList(..), hrlmapa, hrlmap, hrlproj, hrlTravProj,
+  HRList(..), hrlmapa, hrllen, hrlmap, hrlproj, hrlTravProj,
 
   -- * Interoperation between HList and HRList
   HLR(..), hlToHrl,
@@ -87,6 +87,13 @@ instance Show (HRList r '[]) where show _ = "HRN"
 instance (Show (r a), Show (HRList r as)) => Show (HRList r (a ': as)) where
     show (a :++ as) = show a ++ " :+ " ++ show as
 
+hrllen :: HRList r t -> Int
+hrllen = go 0
+ where
+  go :: Int -> HRList r t -> Int
+  go a HRN = a
+  go a (x :++ xs) = a `seq` go (a+1) xs
+
 -- | Shift the type-function of a HRList
 hrlmap :: (forall a . r a -> s a) -> HRList r t -> HRList s t
 hrlmap _  HRN       = HRN
-- 
2.50.1