Add PrimMonad instances

Pointed out at: https://stackoverflow.com/q/52692508/369198

yesod-core/ChangeLog.md

@@ -1,3 +1,10 @@
+# ChangeLog for yesod-core
+
+## 1.6.9
+
+* Add `PrimMonad` instances for `HandlerFor` and `WidgetFor` [from
+  StackOverflow](https://stackoverflow.com/q/52692508/369198)
+
 ## 1.6.8
 
 * Sets the `X-XSS-Protection` header to `1; mode=block` [#1550](https://github.com/yesodweb/yesod/pull/1550)

yesod-core/Yesod/Core/Types.hs

@@ -17,6 +17,7 @@ import           Control.Monad                      (ap)
 import           Control.Monad.IO.Class             (MonadIO (liftIO))
 import           Control.Monad.Logger               (LogLevel, LogSource,
                                                      MonadLogger (..))
+import           Control.Monad.Primitive            (PrimMonad (..))
 import           Control.Monad.Trans.Resource       (MonadResource (..), InternalState, runInternalState, MonadThrow (..), ResourceT)
 import           Data.ByteString                    (ByteString)
 import qualified Data.ByteString.Lazy               as L
@@ -417,6 +418,10 @@ instance Monad (WidgetFor site) where
         unWidgetFor (f a) wd
 instance MonadIO (WidgetFor site) where
     liftIO = WidgetFor . const
+-- | @since 1.6.9
+instance PrimMonad (WidgetFor site) where
+    type PrimState (WidgetFor site) = PrimState IO
+    primitive = liftIO . primitive
 -- | @since 1.4.38
 instance MonadUnliftIO (WidgetFor site) where
   {-# INLINE askUnliftIO #-}
@@ -448,6 +453,10 @@ instance Monad (HandlerFor site) where
     HandlerFor x >>= f = HandlerFor $ \r -> x r >>= \x' -> unHandlerFor (f x') r
 instance MonadIO (HandlerFor site) where
     liftIO = HandlerFor . const
+-- | @since 1.6.9
+instance PrimMonad (HandlerFor site) where
+    type PrimState (HandlerFor site) = PrimState IO
+    primitive = liftIO . primitive
 instance MonadReader (HandlerData site site) (HandlerFor site) where
     ask = HandlerFor return
     local f (HandlerFor g) = HandlerFor $ g . f

yesod-core/yesod-core.cabal

@@ -1,5 +1,5 @@
 name:            yesod-core
-version:         1.6.8
+version:         1.6.9
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -42,6 +42,7 @@ library
                    , mtl
                    , parsec                >= 2        && < 3.2
                    , path-pieces           >= 0.1.2    && < 0.3
+                   , primitive             >= 0.6
                    , random                >= 1.0.0.2  && < 1.2
                    , resourcet             >= 1.2
                    , rio