Add StandaloneDeriving example for DerivingVia.

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Add StandaloneDeriving example for DerivingVia.
[skip-ci]
95521140 · Andreas Klebinger · Marge Bot · 986643cb · 95521140
Commit 95521140 authored Jul 30, 2019 by Andreas Klebinger Committed by Marge Bot Aug 02, 2019
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docs/users_guide/glasgow_exts.rst docs/users_guide/glasgow_exts.rst +6 -0

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--- a/docs/users_guide/glasgow_exts.rst
+++ b/docs/users_guide/glasgow_exts.rst
@@ -5422,6 +5422,12 @@ as in the following example: ::

 Here we make use of the ``Monoid ((->) a)`` instance.

+When used in combination with :extension:`StandaloneDeriving` we swap the order
+for the instance we base our derivation on and the instance we define e.g.: ::
+
+  deriving via (a -> App m b) instance Monoid (Kleisli m a b)
+
+
 .. _pattern-synonyms:

 Pattern synonyms