From f0fd11791c363222d73b34133a87bcb356cd6c26 Mon Sep 17 00:00:00 2001
From: Stephen Diehl <stephen.m.diehl@gmail.com>
Date: Fri, 1 Jul 2016 11:25:10 -0400
Subject: [PATCH] Add unsnoc function.

---
 CHANGES.md       | 1 +
 src/Protolude.hs | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/CHANGES.md b/CHANGES.md
index 099d6444a..2330e0a6f 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -11,6 +11,7 @@
 * Hides all Show class functions. Only the Class itself is exported. Forbids
 * custom instances that are not GHC derived.
 * Export`` encodeUtf8`` and ``decodeUtf8`` functions by default.
+* Adds ``unsnoc`` function.
 
 0.1.5
 =====
diff --git a/src/Protolude.hs b/src/Protolude.hs
index cd79d98d0..429192b01 100644
--- a/src/Protolude.hs
+++ b/src/Protolude.hs
@@ -12,6 +12,7 @@ module Protolude (
   map,
   (&),
   uncons,
+  unsnoc,
   applyN,
   print,
   show,
@@ -362,6 +363,13 @@ uncons :: [a] -> Maybe (a, [a])
 uncons []     = Nothing
 uncons (x:xs) = Just (x, xs)
 
+unsnoc :: [x] -> Maybe ([x],x)
+unsnoc = foldr go Nothing
+  where
+    go x mxs = Just (case mxs of
+       Nothing -> ([], x)
+       Just (xs, e) -> (x:xs, e))
+
 applyN :: Int -> (a -> a) -> a -> a
 applyN n f = X.foldr (.) identity (X.replicate n f)