From 5c9aedaab722490077883869ae80175ee25431dd Mon Sep 17 00:00:00 2001
From: Edward Kmett <ekmett@gmail.com>
Date: Wed, 5 Jun 2019 17:52:56 -0400
Subject: [PATCH] backport pattern synonym

---
 Data/ByteString/Internal.hs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/Data/ByteString/Internal.hs b/Data/ByteString/Internal.hs
index 7ecce7c72..c833bc17b 100644
--- a/Data/ByteString/Internal.hs
+++ b/Data/ByteString/Internal.hs
@@ -1,7 +1,7 @@
 {-# LANGUAGE CPP, ForeignFunctionInterface, BangPatterns #-}
 {-# LANGUAGE UnliftedFFITypes, MagicHash,
             UnboxedTuples, DeriveDataTypeable #-}
-#if __GLASGOW_HASKELL__ >= 806
+#if __GLASGOW_HASKELL__ >= 800
 {-# LANGUAGE PatternSynonyms, ViewPatterns #-}
 #endif
 #if __GLASGOW_HASKELL__ >= 703
@@ -31,7 +31,7 @@ module Data.ByteString.Internal (
         -- * The @ByteString@ type and representation
         ByteString
         ( BS
-#if __GLASGOW_HASKELL__ >= 806
+#if __GLASGOW_HASKELL__ >= 800
         , PS -- backwards compatibility shim
 #endif
         ), -- instances: Eq, Ord, Show, Read, Data, Typeable
@@ -180,10 +180,9 @@ data ByteString = BS {-# UNPACK #-} !(ForeignPtr Word8) -- payload
     deriving (Typeable)
 
 
-#if __GLASGOW_HASKELL__ >= 806
--- on GHC-8.0 ... 8.6: Pattern synonym definition cannot contain as-patterns (@)
+#if __GLASGOW_HASKELL__ >= 800
 pattern PS :: ForeignPtr Word8 -> Int -> Int -> ByteString
-pattern PS fp o len <- BS fp len@(const 0 -> o) where
+pattern PS fp zero len <- BS fp (((,) 0) -> (zero, len)) where
   PS fp o len = BS (plusForeignPtr fp o) len
 #endif