From 95d1a34e9491e399643c384bb807e538b6100ac1 Mon Sep 17 00:00:00 2001
From: Kei Hibino <ex8k.hibino@gmail.com>
Date: Sun, 30 Apr 2017 23:08:44 +0900
Subject: [PATCH] relational-query: update haddock of ShowConstantTermsSQL.

---
 .../Relational/Query/ProjectableClass.hs       | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/relational-query/src/Database/Relational/Query/ProjectableClass.hs b/relational-query/src/Database/Relational/Query/ProjectableClass.hs
index 5e182999..b125751b 100644
--- a/relational-query/src/Database/Relational/Query/ProjectableClass.hs
+++ b/relational-query/src/Database/Relational/Query/ProjectableClass.hs
@@ -61,7 +61,23 @@ showConstantTermsSQL :: ShowConstantTermsSQL a
                      -> [StringSQL]
 showConstantTermsSQL = toList . showConstantTermsSQL'
 
--- | Interface for constant SQL term list.
+{- |
+'ShowConstantTermsSQL' 'a' is implicit rule to derive function to convert
+from haskell record type 'a' into constant SQL terms.
+
+Generic programming (<https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#generic-programming>)
+with default signature is available for 'ShowConstantTermsSQL' class,
+so you can make instance like below:
+
+@
+  \{\-\# LANGUAGE DeriveGeneric \#\-\}
+  import GHC.Generics (Generic)
+  --
+  data Foo = Foo { ... } deriving Generic
+  instance ShowConstantTermsSQL Foo
+@
+
+-}
 class ShowConstantTermsSQL a where
   showConstantTermsSQL' :: a -> DList StringSQL