Add Functor and Bifunctor instance for pairs (#416)

* Add Functor and Bifunctor instance for pairs

* Add since

* changelog entry

changelog.md

@@ -3,6 +3,8 @@
 - @parsonsmatt
     - [#414](https://github.com/bitemyapp/esqueleto/pull/414)
         - Derive `Foldable` and `Traversable` for `Value`.
+    - [#416](https://github.com/bitemyapp/esqueleto/pull/416)
+        - Derive `Functor` and `Bifunctor` for `:&`
 - @matthewbauer
     - [#341](https://github.com/bitemyapp/esqueleto/pull/341/)
         - Add functions for `NULLS FIRST` and `NULLS LAST` in the Postgresql

src/Database/Esqueleto/Internal/Internal.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE TypeApplications #-}
@@ -54,6 +55,7 @@ import qualified Control.Monad.Trans.Reader as R
 import qualified Control.Monad.Trans.State as S
 import qualified Control.Monad.Trans.Writer as W
 import qualified Data.ByteString as B
+import Data.Bifunctor (Bifunctor, bimap)
 import Data.Coerce (coerce)
 import qualified Data.Conduit as C
 import qualified Data.Conduit.List as CL
@@ -1551,9 +1553,15 @@ data Insertion a
 -- See the examples at the beginning of this module to see how this
 -- operator is used in 'JOIN' operations.
 data (:&) a b = a :& b
-    deriving (Eq, Show)
+    deriving (Eq, Show, Functor)
 infixl 2 :&
 
+-- |
+--
+-- @since 3.5.14.0
+instance Bifunctor (:&) where
+    bimap f g (a :& b) = f a :& g b
+
 -- | Different kinds of locking clauses supported by 'locking'.
 --
 -- Note that each RDBMS has different locking support.  The