drop

2 files changed, 34 insertions, 20 deletions

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index 690d66e..6f42f9c 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -121,6 +121,24 @@ pub fn take(from iterator: Iterator(e), up_to desired: Int) -> List(e) {
   |> list.reverse
 }
 
+fn do_drop(iterator, desired) {
+  case desired > 0 {
+    True -> case iterator() {
+      Continue(_, iterator) -> do_drop(iterator, desired - 1)
+      Stop -> fn() { Stop }
+    }
+    False -> iterator
+  }
+}
+
+// TODO: document
+pub fn drop(from iterator: Iterator(e), up_to desired: Int) -> Iterator(e) {
+  iterator
+  |> unopaque
+  |> do_drop(_, desired)
+  |> opaque
+}
+
 // Transforming Iterators
 
 fn do_map(iterator, f) {
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index 079d57d..936621e 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -119,27 +119,23 @@ pub fn unfold_test() {
 }
 
 pub fn range_test() {
-  iterator.range(0, 0)
-  |> iterator.to_list
-  |> expect.equal(_, [])
-
-  iterator.range(1, 1)
-  |> iterator.to_list
-  |> expect.equal(_, [])
-
-  iterator.range(-1, -1)
-  |> iterator.to_list
-  |> expect.equal(_, [])
-
-  iterator.range(0, 1)
-  |> iterator.to_list
-  |> expect.equal(_, [0])
+  let test = fn(a, b, expected) {
+    iterator.range(a, b)
+    |> iterator.to_list
+    |> expect.equal(_, expected)
+  }
 
-  iterator.range(0, 5)
-  |> iterator.to_list
-  |> expect.equal(_, [0, 1, 2, 3, 4])
+  test(0, 0, [])
+  test(1, 1, [])
+  test(-1, -1, [])
+  test(0, 1, [0])
+  test(0, 5, [0, 1, 2, 3, 4])
+  test(1, -5, [1, 0, -1, -2, -3, -4])
+}
 
-  iterator.range(1, -5)
+pub fn drop_test() {
+  iterator.range(0, 10)
+  |> iterator.drop(_, 5)
   |> iterator.to_list
-  |> expect.equal(_, [1, 0, -1, -2, -3, -4])
+  |> expect.equal(_, [5, 6, 7, 8, 9])
 }