Add moveStart and moveEnd functions

README.md

@@ -22,14 +22,8 @@ Currently this library provides bunch of instances: `Foldable`, `Foldable1`, `Tr
 
 Additionally it implements following operations:
 
-* `prev` / `next` - O(1)
-* `insertLeft` / `insertRight` - O(1)
-* `deleteLeft` / `deleteRight` - O(1)
-* `replace` - O(1)
-* `dropSuffix` - O(1)
-* `dropPrefix` - O(1)
-* `atEnd` - O(1)
-* `atStart` - O(1)
+* `prev`, `next`, `insertLeft`, `insertRight`, `deleteLeft`, `deleteRight`, `replace`, `dropPrefix`, `dropSuffix`, `atStart`, `atEnd` - O(1)
+* `moveStart`, `moveEnd` - O(n)
 
 ## Usage example
 

src/Data/List/Pointed.purs

@@ -5,7 +5,6 @@ import Prelude
 import Control.Comonad (class Comonad, class Extend)
 import Data.Foldable (class Foldable, foldl, foldMap, foldr)
 import Data.List (List(..), reverse, uncons)
-import Data.List (fromFoldable) as List
 import Data.Maybe (Maybe(..))
 import Data.Newtype (class Newtype)
 import Data.Semigroup.Foldable (class Foldable1)
@@ -109,11 +108,13 @@ insertRight a (Pointed { focus, reversedPrefix, suffix }) = Pointed
   , suffix
   }
 
+-- | Delete current `focus` and move to the left if possible.
 deleteLeft ∷ ∀ a. Pointed a → Maybe (Pointed a)
 deleteLeft (Pointed { focus, reversedPrefix, suffix }) =
   uncons reversedPrefix <#> \{ head, tail } → Pointed
     { focus: head, reversedPrefix: tail, suffix }
 
+-- | Delete current `focus` and move to the right if possible.
 deleteRight ∷ ∀ a. Pointed a → Maybe (Pointed a)
 deleteRight (Pointed { focus, reversedPrefix, suffix }) =
   uncons suffix <#> \{ head, tail } → Pointed
@@ -127,6 +128,24 @@ dropSuffix ∷ ∀ a. Pointed a → Pointed a
 dropSuffix (Pointed { focus, reversedPrefix }) =
   Pointed { focus, reversedPrefix, suffix: Nil }
 
+moveStart ∷ ∀ a. Pointed a → Pointed a
+moveStart p@(Pointed { focus, reversedPrefix, suffix }) = case uncons (reverse <<< Cons focus $ reversedPrefix) of
+  Just { head, tail } → Pointed
+    { focus: head
+    , reversedPrefix: Nil
+    , suffix: tail <> suffix
+    }
+  Nothing → p
+
+moveEnd ∷ ∀ a. Pointed a → Pointed a
+moveEnd p@(Pointed { focus, reversedPrefix, suffix }) = case uncons (reverse <<< Cons focus $ suffix) of
+  Just { head, tail } → Pointed
+    { focus: head
+    , reversedPrefix: tail <> reversedPrefix
+    , suffix: Nil
+    }
+  Nothing → p
+
 atStart ∷ ∀ a. Pointed a → Boolean
 atStart (Pointed { reversedPrefix: Nil }) = true
 atStart _ = false

test/Main.purs

@@ -3,11 +3,11 @@ module Test.Main where
 import Prelude
 
 import Control.Comonad (extend, extract)
-import Data.Array (fromFoldable, snoc) as Array
 import Data.Array (foldl, foldr)
+import Data.Array (fromFoldable, snoc) as Array
 import Data.Foldable (fold, foldMap, sum)
 import Data.List (length) as List
-import Data.List.Pointed (Pointed(..), fromFoldable, insertLeft, insertRight, prev)
+import Data.List.Pointed (Pointed(..), atEnd, atStart, fromFoldable, insertLeft, insertRight, moveEnd, moveStart, prev)
 import Data.List.Pointed (fromFoldable) as Pointed
 import Data.Maybe (Maybe(..))
 import Data.Monoid.Additive (Additive(..))
@@ -17,6 +17,7 @@ import Test.Unit (suite, test)
 import Test.Unit.Assert (equal)
 import Test.Unit.Main (runTest)
 
+
 main :: Effect Unit
 main = runTest $ do
   suite "Data.List.Pointed" $ do
@@ -125,3 +126,19 @@ main = runTest $ do
     test "foldMap from the end" do
       let r = map (foldMap identity) (fromFoldable ["1", "2", "3", "4", "5"])
       equal (Just "12345") r
+
+
+    test "moveEnd" $ do
+      let
+        arr =  ["1", "2", "3", "4", "5"]
+        r = prev =<< fromFoldable arr
+      equal (Just false) (atEnd <$> r)
+      equal (Just true) (atEnd <<< moveEnd <$> r)
+      equal (Just arr) (Array.fromFoldable <<< moveEnd <$> r)
+    test "moveStart" $ do
+      let
+        arr =  ["1", "2", "3", "4", "5"]
+        r = prev =<< fromFoldable arr
+      equal (Just false) (atStart <$> r)
+      equal (Just true) (atStart <<< moveStart <$> r)
+      equal (Just arr) (Array.fromFoldable <<< moveStart <$> r)