diff -r 5721f1843e93 -r 1d26f1a49480 src/Tools/Haskell/Haskell.thy
--- a/src/Tools/Haskell/Haskell.thy	Sat Jul 31 12:23:15 2021 +0200
+++ b/src/Tools/Haskell/Haskell.thy	Sat Jul 31 12:24:13 2021 +0200
@@ -250,7 +250,7 @@
         Just y -> Just (i, y)
 
 separate :: a -> [a] -> [a]
-separate s (x : (xs @ (_ : _))) = x : s : separate s xs
+separate s (x : xs @ (_ : _)) = x : s : separate s xs
 separate _ xs = xs;