From 6003c596d7b348b29dd4f452f504bfd717634fa2 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Fri, 10 Aug 2018 15:44:20 -0700
Subject: Avoid non-exhaustive pattern match.

---
 src/Text/Pandoc/UUID.hs | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

(limited to 'src/Text')

diff --git a/src/Text/Pandoc/UUID.hs b/src/Text/Pandoc/UUID.hs
index c1bae7038..60ff269da 100644
--- a/src/Text/Pandoc/UUID.hs
+++ b/src/Text/Pandoc/UUID.hs
@@ -67,13 +67,14 @@ instance Show UUID where
 
 getUUID :: RandomGen g => g -> UUID
 getUUID gen =
-  let [a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p] = take 16 $ randoms gen :: [Word8]
-  -- set variant
-      i' = i `setBit` 7 `clearBit` 6
-  -- set version (0100 for random)
-      g' = g `clearBit` 7 `setBit` 6 `clearBit` 5 `clearBit` 4
-  in
-    UUID a b c d e f g' h i' j k l m n o p
+  case take 16 (randoms gen :: [Word8]) of
+       [a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p] ->
+         -- set variant
+         let i' = i `setBit` 7 `clearBit` 6
+         -- set version (0100 for random)
+             g' = g `clearBit` 7 `setBit` 6 `clearBit` 5 `clearBit` 4
+         in  UUID a b c d e f g' h i' j k l m n o p
+       _ -> error "not enough random numbers for UUID" -- should not happen
 
 getRandomUUID :: IO UUID
 getRandomUUID = getUUID <$> getStdGen
-- 
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