From d4fbf0f1218592191a37be594e3a018ef6e18ef8 Mon Sep 17 00:00:00 2001
From: NicklasXYZ <nsa200293@live.dk>
Date: Sat, 28 Jan 2023 21:53:44 +0100
Subject: [PATCH] Work on int_list module

---
 src/gleam_community/maths/int_list.gleam      | 97 +++++++++++++++++++
 .../gleam_community_maths_int_list_test.gleam | 24 +++++
 2 files changed, 121 insertions(+)

diff --git a/src/gleam_community/maths/int_list.gleam b/src/gleam_community/maths/int_list.gleam
index 99e99a2..c4439af 100644
--- a/src/gleam_community/maths/int_list.gleam
+++ b/src/gleam_community/maths/int_list.gleam
@@ -42,6 +42,103 @@ import gleam/float
 import gleam/pair
 import gleam_community/maths/int as intx
 
+/// <div style="text-align: right;">
+///     <a href="https://github.com/gleam-community/maths/issues">
+///         <small>Spot a typo? Open an issue!</small>
+///     </a>
+/// </div>
+///
+/// Calculcate the cumulative sum of the elements in a list:
+///
+/// \\[
+/// v_j = \sum_{i=1}^j x_i, \forall j \leq n
+/// \\]
+///
+/// In the formula, $$n$$ is the length of the list and $$x_i$$ is the value in the input list indexed by $$i$$.
+/// Furthermore, $$v_j$$ is the $$j$$th element in the cumulative sum.
+///
+/// <details>
+///     <summary>Example:</summary>
+///
+///     import gleeunit/should
+///     import gleam_community/maths/int_list
+///
+///     pub fn example () {
+///       []
+///       |> int_list.cumulative_sum()
+///       |> should.equal([])
+///
+///       // Valid input returns a result
+///       [1, 2, 3]
+///       |> int_list.cumulative_sum()
+///       |> should.equal([1, 3, 6])
+///     }
+/// </details>
+///
+/// <div style="text-align: right;">
+///     <a href="#">
+///         <small>Back to top ↑</small>
+///     </a>
+/// </div>
+///
+pub fn cumulative_sum(arr: List(Int)) -> List(Int) {
+  case arr {
+    [] -> []
+    _ ->
+      arr
+      |> list.scan(0, fn(acc: Int, a: Int) -> Int { a + acc })
+  }
+}
+
+/// <div style="text-align: right;">
+///     <a href="https://github.com/gleam-community/maths/issues">
+///         <small>Spot a typo? Open an issue!</small>
+///     </a>
+/// </div>
+///
+/// Calculcate the cumulative product of the elements in a list:
+///
+/// \\[
+/// v_j = \prod_{i=1}^j x_i, \forall j \leq n
+/// \\]
+///
+/// In the formula, $$n$$ is the length of the list and $$x_i$$ is the value in the input list indexed by $$i$$.
+/// Furthermore, $$v_j$$ is the $$j$$th element in the cumulative product.
+///
+/// <details>
+///     <summary>Example:</summary>
+///
+///     import gleeunit/should
+///     import gleam_community/maths/int_list
+///
+///     pub fn example () {
+///       // An empty list returns an error
+///       []
+///       |> int_list.cumulative_product()
+///       |> should.equal([])
+///
+///       // Valid input returns a result
+///       [1, 2, 3]
+///       |> int_list.cumulative_product()
+///       |> should.equal([1, 2, 6])
+///     }
+/// </details>
+///
+/// <div style="text-align: right;">
+///     <a href="#">
+///         <small>Back to top ↑</small>
+///     </a>
+/// </div>
+///
+pub fn cumumlative_product(arr: List(Int)) -> List(Int) {
+  case arr {
+    [] -> []
+    _ ->
+      arr
+      |> list.scan(1, fn(acc: Int, a: Int) -> Int { a * acc })
+  }
+}
+
 /// <div style="text-align: right;">
 ///     <a href="https://github.com/gleam-community/maths/issues">
 ///         <small>Spot a typo? Open an issue!</small>
diff --git a/test/gleam/gleam_community_maths_int_list_test.gleam b/test/gleam/gleam_community_maths_int_list_test.gleam
index 8dfcdba..1be0e4e 100644
--- a/test/gleam/gleam_community_maths_int_list_test.gleam
+++ b/test/gleam/gleam_community_maths_int_list_test.gleam
@@ -68,3 +68,27 @@ pub fn int_list_extrema_test() {
   |> int_list.extrema()
   |> should.equal(Ok(#(1, 4)))
 }
+
+pub fn int_list_cumulative_sum_test() {
+  // An empty lists returns an empty list
+  []
+  |> int_list.cumulative_sum()
+  |> should.equal([])
+
+  // Valid input returns a result
+  [1, 2, 3]
+  |> int_list.cumulative_sum()
+  |> should.equal([1, 3, 6])
+}
+
+pub fn int_list_cumulative_product_test() {
+  // An empty lists returns an empty list
+  []
+  |> int_list.cumumlative_product()
+  |> should.equal([])
+
+  // Valid input returns a result
+  [1, 2, 3]
+  |> int_list.cumumlative_product()
+  |> should.equal([1, 2, 6])
+}