From 14c35e022591a88c5142a9c63dd99419070479f0 Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Thu, 2 Jun 2016 09:47:37 -0700
Subject: [PATCH] Add moral Functor constraint for to and friends

---
 src/Control/Lens/Getter.hs | 15 +++++++++++----
 src/Control/Lens/Review.hs |  2 +-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/Control/Lens/Getter.hs b/src/Control/Lens/Getter.hs
index 0be4c4b6e..936e2e57a 100644
--- a/src/Control/Lens/Getter.hs
+++ b/src/Control/Lens/Getter.hs
@@ -16,6 +16,13 @@
 {-# LANGUAGE NoPolyKinds #-}
 {-# LANGUAGE NoDataKinds #-}
 #endif
+
+-- Disable the warnings generated by 'to', 'ito', 'like', 'ilike'.
+-- These functions are intended to produce 'Getters'. Without this constraint
+-- users would get warnings when annotating types at uses of these functions.
+#if __GLASGOW_HASKELL__ >= 711
+{-# OPTIONS_GHC -fno-warn-redundant-constraints #-}
+#endif
 -------------------------------------------------------------------------------
 -- |
 -- Module      :  Control.Lens.Getter
@@ -137,7 +144,7 @@ infixl 8 ^., ^@.
 -- @
 -- 'to' :: (s -> a) -> 'IndexPreservingGetter' s a
 -- @
-to :: (Profunctor p, Contravariant f) => (s -> a) -> Optic' p f s a
+to :: (Profunctor p, Contravariant f, Functor f) => (s -> a) -> Optic' p f s a
 to k = dimap k (contramap k)
 {-# INLINE to #-}
 
@@ -145,7 +152,7 @@ to k = dimap k (contramap k)
 -- @
 -- 'ito' :: (s -> (i, a)) -> 'IndexedGetter' i s a
 -- @
-ito :: (Indexable i p, Contravariant f) => (s -> (i, a)) -> Over' p f s a
+ito :: (Indexable i p, Contravariant f, Functor f) => (s -> (i, a)) -> Over' p f s a
 ito k = dimap k (contramap (snd . k)) . uncurry . indexed
 {-# INLINE ito #-}
 
@@ -164,7 +171,7 @@ ito k = dimap k (contramap (snd . k)) . uncurry . indexed
 -- @
 -- 'like' :: a -> 'IndexPreservingGetter' s a
 -- @
-like :: (Profunctor p, Contravariant f) => a -> Optic' p f s a
+like :: (Profunctor p, Contravariant f, Functor f) => a -> Optic' p f s a
 like a = to (const a)
 {-# INLINE like #-}
 
@@ -172,7 +179,7 @@ like a = to (const a)
 -- @
 -- 'ilike' :: i -> a -> 'IndexedGetter' i s a
 -- @
-ilike :: (Indexable i p, Contravariant f) => i -> a -> Over' p f s a
+ilike :: (Indexable i p, Contravariant f, Functor f) => i -> a -> Over' p f s a
 ilike i a = ito (const (i, a))
 {-# INLINE ilike #-}
 
diff --git a/src/Control/Lens/Review.hs b/src/Control/Lens/Review.hs
index 62abb7d38..c2ac8d76c 100644
--- a/src/Control/Lens/Review.hs
+++ b/src/Control/Lens/Review.hs
@@ -108,7 +108,7 @@ un = unto . view
 -- 're' :: 'Prism' s t a b -> 'Getter' b t
 -- 're' :: 'Iso' s t a b   -> 'Getter' b t
 -- @
-re :: Contravariant f => AReview t b -> LensLike' f b t
+re :: AReview t b -> Getter b t
 re p = to (runIdentity #. unTagged #. p .# Tagged .# Identity)
 {-# INLINE re #-}