feat(int): add sum function

2 files changed, 27 insertions, 0 deletions

diff --git a/src/gleam/int.gleam b/src/gleam/int.gleam
index f717eaa..0bbd63d 100644
--- a/src/gleam/int.gleam
+++ b/src/gleam/int.gleam
@@ -148,3 +148,22 @@ pub fn is_odd(x: Int) -> Bool {
 pub fn negate(x: Int) -> Int {
   -1 * x
 }
+
+/// Sums a list of Ints.
+///
+/// ## Example
+///
+///    > sum([1, 2, 3])
+///    6
+///
+pub fn sum(numbers: List(Int)) -> Int {
+  numbers
+  |> do_sum(0)
+}
+
+fn do_sum(numbers: List(Int), initial: Int) -> Int {
+  case numbers {
+    [] -> initial
+    [x, ..rest] -> do_sum(rest, x + initial)
+  }
+}
diff --git a/test/gleam/int_test.gleam b/test/gleam/int_test.gleam
index 97fbb84..cd7b2b9 100644
--- a/test/gleam/int_test.gleam
+++ b/test/gleam/int_test.gleam
@@ -182,3 +182,11 @@ pub fn negate_test() {
   int.negate(0)
   |> should.equal(0)
 }
+
+pub fn sum_test() {
+  int.sum([])
+  |> should.equal(0)
+
+  int.sum([1, 2, 3])
+  |> should.equal(6)
+}