This patch is taken from upstream.  It fixes a test to work with GHC 8.6.
The paths have been slightly altered to work with the release tarball.

See <https://github.com/simonmar/monad-par/issues/66>.

From e20f81c8060208e4fb038e8f0e0668b41d72a6fb Mon Sep 17 00:00:00 2001
From: Clint Adams <clint@debian.org>
Date: Sat, 31 Aug 2019 14:12:34 -0400
Subject: [PATCH] Use a case statement instead of pattern-matching in
 case_test_diamond

This avoids the need for a MonadFail instance.  Closes #66
---
 monad-par/tests/ParTests_shared.hs | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/tests/ParTests_shared.hs b/tests/ParTests_shared.hs
index 31f438d..b2de50c 100644
--- a/tests/ParTests_shared.hs
+++ b/tests/ParTests_shared.hs
@@ -109,12 +109,15 @@ case_test_diamond :: Assertion
 case_test_diamond = 9 @=? (m :: Int)
  where 
   m = runPar $ do
-      [a,b,c,d] <- sequence [new,new,new,new]
-      fork $ do x <- get a; put b (x+1)
-      fork $ do x <- get a; put c (x+2)
-      fork $ do x <- get b; y <- get c; put d (x+y)
-      fork $ do put a 3
-      get d
+      abcd <- sequence [new,new,new,new]
+      case abcd of
+          [a,b,c,d] -> do
+              fork $ do x <- get a; put b (x+1)
+              fork $ do x <- get a; put c (x+2)
+              fork $ do x <- get b; y <- get c; put d (x+y)
+              fork $ do put a 3
+              get d
+          _ -> error "Oops"
 
 -- | Violate IVar single-assignment:
 --
-- 
2.23.0

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<div class='path'>path: <a href='/guix/log/?id=84780ff427364fdd2f158b1f7439debee2bf3799'>root</a>/<a href='/guix/log/TODO?id=84780ff427364fdd2f158b1f7439debee2bf3799'>TODO</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/TODO?id=84780ff427364fdd2f158b1f7439debee2bf3799&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-01-21 09:59:41 +0100'>2019-01-21</span></td><td><a href='/guix/commit/TODO?id=b93d2602f72dbbd9334a4f5c75b8721e1f2fa35a'>Update 'TODO'</a><span class='msg-avail'>...<span class='msg-tooltip'>* TODO (Installer): Add Pierre Neidhardt suggestions described here:
  https://lists.gnu.org/archive/html/guix-devel/2019-01/msg00305.html
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2019-01-17 14:11:15 +0100'>2019-01-17</span></td><td><a href='/guix/commit/TODO?id=11b68c90cd89288906c595d5c31a0413ed8a496f'>Update 'TODO'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* TODO (Installer): New section.
</span></span></td><td>Mathieu Othacehe</td></tr>