Add Semigroup/Monoid for Q (#18123)

2 files changed, 11 insertions, 0 deletions

diff --git a/libraries/template-haskell/Language/Haskell/TH/Syntax.hs b/libraries/template-haskell/Language/Haskell/TH/Syntax.hs
index 60fb9d37ca..d994aa686d 100644
--- a/libraries/template-haskell/Language/Haskell/TH/Syntax.hs
+++ b/libraries/template-haskell/Language/Haskell/TH/Syntax.hs
@@ -33,6 +33,7 @@ import Data.IORef
 import System.IO.Unsafe ( unsafePerformIO )
 import Control.Monad (liftM)
 import Control.Monad.IO.Class (MonadIO (..))
+import Control.Applicative (liftA2)
 import System.IO        ( hPutStrLn, stderr )
 import Data.Char        ( isAlpha, isAlphaNum, isUpper, ord )
 import Data.Int
@@ -206,6 +207,14 @@ instance Applicative Q where
   Q f <*> Q x = Q (f <*> x)
   Q m *> Q n = Q (m *> n)
 
+-- | @since 2.17.0.0
+instance Semigroup a => Semigroup (Q a) where
+  (<>) = liftA2 (<>)
+
+-- | @since 2.17.0.0
+instance Monoid a => Monoid (Q a) where
+  mempty = pure mempty
+
 -----------------------------------------------------
 --
 --              The Quote class
diff --git a/libraries/template-haskell/changelog.md b/libraries/template-haskell/changelog.md
index 55aab10c0d..24a74e4616 100644
--- a/libraries/template-haskell/changelog.md
+++ b/libraries/template-haskell/changelog.md
@@ -22,6 +22,8 @@
   * Fix Show instance for `Bytes`: we were showing the pointer value while we
     want to show the contents (#16457).
 
+  * Add `Semigroup` and `Monoid` instances for `Q` (#18123).
+
 ## 2.16.0.0 *TBA*
 
   * Add support for tuple sections. (#15843) The type signatures of `TupE` and