From 4dc84dbda7ba3ea60d13e6f81eeec556974b7c72 Mon Sep 17 00:00:00 2001
From: Joris
Date: Thu, 7 Nov 2019 07:59:41 +0100
Subject: Show payment header infos

---
 server/src/Util/List.hs | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 server/src/Util/List.hs

(limited to 'server/src/Util/List.hs')

diff --git a/server/src/Util/List.hs b/server/src/Util/List.hs
new file mode 100644
index 0000000..4e22ba8
--- /dev/null
+++ b/server/src/Util/List.hs
@@ -0,0 +1,13 @@
+module Util.List
+  ( groupBy
+  ) where
+
+import           Control.Arrow ((&&&))
+import           Data.Function (on)
+import qualified Data.List     as L
+
+groupBy :: forall a b. (Ord b) => (a -> b) -> [a] -> [(b, [a])]
+groupBy f =
+  map (f . head &&& id)
+    . L.groupBy ((==) `on` f)
+    . L.sortBy (compare `on` f)
-- 
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