shrink 'swap'

StackSet.hs

@@ -202,14 +202,11 @@ promote w = maybe w id $ do
 -- > swap a b . swap a b == id
 --
 swap :: Eq a => a -> a -> [a] -> [a]
-swap a b xs
-    | a == b                    = xs    -- do nothing
-    | Just ai <- L.elemIndex a xs
-    , Just bi <- L.elemIndex b xs = insertAt bi a (insertAt ai b xs)
- where
-    insertAt n x ys = as ++ x : tail bs
-        where (as,bs) = splitAt n ys
-
+swap a b xs | a == b  = xs    -- do nothing
+            | Just ai <- L.elemIndex a xs
+            , Just bi <- L.elemIndex b xs = insertAt bi a (insertAt ai b xs)
+  where insertAt n x ys = as ++ x : tail bs
+            where (as,bs) = splitAt n ys
 swap _ _ xs = xs -- do nothing
 
 --