List: add instance Splittable Seq

Add an instance of Splittable for Data.Sequence.Seq, and QuickCheck
properties for it.

Add lower bound containers >= 0.5.7, being the version at which the
Semigroup instance was introduced.

brick.cabal

@@ -94,7 +94,7 @@ library
                        directory >= 1.2.5.0,
                        dlist,
                        filepath,
-                       containers,
+                       containers >= 0.5.7,
                        microlens >= 0.3.0.0,
                        microlens-th,
                        microlens-mtl,

src/Brick/Widgets/List.hs

@@ -79,6 +79,7 @@ import Data.Foldable (find, toList)
 import Data.List.NonEmpty (NonEmpty((:|)))
 import Data.Maybe (fromMaybe)
 import Data.Semigroup (Semigroup, (<>), sconcat)
+import qualified Data.Sequence as Seq
 import Graphics.Vty (Event(..), Key(..), Modifier(..))
 import qualified Data.Vector as V
 import GHC.Generics (Generic)
@@ -140,6 +141,11 @@ class Splittable t where
 
   -- | Slice the structure.  Equivalent to @(take n . drop i) xs@,
   -- therefore total.
+  --
+  -- The default implementation applies 'splitAt' two times: first
+  -- to drop elements leading up to the slice, and again to drop
+  -- elements after the slice.
+  --
   slice :: Int {- ^ start index -} -> Int {- ^ length -} -> t a -> t a
   slice i n = fst . splitAt n . snd . splitAt i
 
@@ -147,6 +153,10 @@ class Splittable t where
 instance Splittable V.Vector where
   splitAt = V.splitAt
 
+-- | /O(log(min(i,n-i)))/ 'splitAt'.
+instance Splittable Seq.Seq where
+  splitAt = Seq.splitAt
+
 
 handleListEvent
   :: (Foldable t, Splittable t, Ord n)

tests/List.hs

@@ -14,6 +14,7 @@ import Data.Maybe (isNothing)
 import Data.Monoid (Endo(..))
 import Data.Semigroup (Semigroup((<>)))
 
+import qualified Data.Sequence as Seq
 import qualified Data.Vector as V
 import Lens.Micro
 import Test.QuickCheck
@@ -272,6 +273,12 @@ prop_splitAtLength_Vector = splitAtLength . V.fromList
 prop_splitAtAppend_Vector :: (Eq a) => [a] -> Int -> Bool
 prop_splitAtAppend_Vector = splitAtAppend . V.fromList
 
+prop_splitAtLength_Seq :: [a] -> Int -> Bool
+prop_splitAtLength_Seq = splitAtLength . Seq.fromList
+
+prop_splitAtAppend_Seq :: (Eq a) => [a] -> Int -> Bool
+prop_splitAtAppend_Seq = splitAtAppend . Seq.fromList
+
 
 return []