feat(Array): add dropLast and dropRight functions

core/core/Array.hs

@@ -25,6 +25,8 @@ module Array (
   set,
   push,
   append,
+  dropLast,
+  dropRight,
   slice,
 
   -- * LinkedLists
@@ -575,6 +577,39 @@ indexed :: Array a -> Array (Int, a)
 indexed (Array vector) = Array (Data.Vector.indexed vector)
 
 
+-- | Remove the last element of an array.
+-- Returns the original array when it is empty.
+--
+-- >>> dropLast (fromLinkedList [1,2,3] :: Array Int)
+-- Array [1,2]
+-- >>> dropLast (fromLinkedList [] :: Array Int)
+-- Array []
+dropLast :: Array element -> Array element
+dropLast arr =
+  if isEmpty arr
+    then arr
+    else take (length arr - 1) arr
+
+
+-- | Remove the last @n@ elements from an array.
+-- When @n <= 0@, returns the original array.
+-- When @n >= length@, returns an empty array.
+--
+-- >>> dropRight 2 (fromLinkedList [1,2,3] :: Array Int)
+-- Array [1]
+-- >>> dropRight 0 (fromLinkedList [1,2,3] :: Array Int)
+-- Array [1,2,3]
+-- >>> dropRight 5 (fromLinkedList [1,2,3] :: Array Int)
+-- Array []
+dropRight :: Int -> Array element -> Array element
+dropRight n arr = do
+  let len = length arr
+      keep = max 0 (len - n)
+  if keep == len
+    then arr
+    else take keep arr
+
+
 -- | Zip two arrays into a new array of tuples.
 -- >>> (fromLinkedList [1,2,3] :: Array Int) |> zip (fromLinkedList [4,5,6] :: Array Int)
 -- Array [(1,4),(2,5),(3,6)]

core/test/ArraySpec.hs

@@ -0,0 +1,27 @@
+{-# OPTIONS_GHC -Wno-unused-imports #-}
+
+module ArraySpec where
+
+import Array qualified
+import Test
+
+spec :: Spec Unit
+spec = do
+  describe "Array" do
+    describe "dropLast" do
+      it "removes the final element" \_ -> do
+        Array.fromLinkedList [1, 2, 3] |> Array.dropLast |> shouldBe (Array.fromLinkedList [1, 2])
+
+      it "returns the same empty array" \_ -> do
+        Array.empty |> Array.dropLast |> shouldBe (Array.empty :: Array.Array Int)
+
+    describe "dropRight" do
+      it "drops the last n elements" \_ -> do
+        Array.fromLinkedList [1, 2, 3, 4] |> Array.dropRight 2 |> shouldBe (Array.fromLinkedList [1, 2])
+
+      it "returns the original array when n is zero" \_ -> do
+        Array.fromLinkedList [1, 2, 3] |> Array.dropRight 0 |> shouldBe (Array.fromLinkedList [1, 2, 3])
+
+      it "returns an empty array when n is at least the length" \_ -> do
+        Array.fromLinkedList [1, 2, 3] |> Array.dropRight 3 |> shouldBe (Array.empty :: Array.Array Int)
+        Array.fromLinkedList [1, 2, 3] |> Array.dropRight 5 |> shouldBe (Array.empty :: Array.Array Int)