list.key_set

3 files changed, 37 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f706231..508db58 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
   `of`.
 - The `dynamic` module gains the `any` function.
 - The `bit_builder` module gains the `from_string` function.
+- The `list` module gains the `key_set` function.
 
 ## v0.10.1 - 2020-07-01
 
diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index b13575b..06e5a33 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -954,7 +954,10 @@ pub fn pop_map(
 ///    > key_pop([tuple("a", 0), tuple("b", 1)], "c")
 ///    Error(Nil)
 ///
-pub fn key_pop(haystack, key) {
+pub fn key_pop(
+  haystack: List(tuple(k, v)),
+  key: k,
+) -> Result(tuple(v, List(tuple(k, v))), Nil) {
   pop_map(
     haystack,
     fn(entry) {
@@ -966,3 +969,25 @@ pub fn key_pop(haystack, key) {
     },
   )
 }
+
+/// Given a list of 2 element tuples, insert a key and value into the list.
+///
+/// If there was already a tuple with the key then it is replaced, otherwise it
+/// is added to the end of the list.
+///
+///
+/// ## Examples
+///
+///    > key_set([tuple(5, 0), tuple(4, 1)], 4, 100)
+///    [tuple(5, 0), tuple(4, 100)]
+///
+///    > key_set([tuple(5, 0), tuple(4, 1)], 1, 100)
+///    [tuple(5, 0), tuple(4, 1), tuple(1, 100)]
+///
+pub fn key_set(list: List(tuple(a, b)), key: a, value: b) -> List(tuple(a, b)) {
+  case list {
+    [] -> [tuple(key, value)]
+    [tuple(k, _), ..rest] if k == key -> [tuple(key, value), ..rest]
+    [first, ..rest] -> [first, ..key_set(rest, key, value)]
+  }
+}
diff --git a/test/gleam/list_test.gleam b/test/gleam/list_test.gleam
index ef096f6..31f8f27 100644
--- a/test/gleam/list_test.gleam
+++ b/test/gleam/list_test.gleam
@@ -457,3 +457,13 @@ pub fn key_pop_test() {
   list.key_pop([tuple("a", 0), tuple("b", 1)], "c")
   |> should.equal(Error(Nil))
 }
+
+pub fn key_set_test() {
+  [tuple(5, 0), tuple(4, 1)]
+  |> list.key_set(4, 100)
+  |> should.equal([tuple(5, 0), tuple(4, 100)])
+
+  [tuple(5, 0), tuple(4, 1)]
+  |> list.key_set(1, 100)
+  |> should.equal([tuple(5, 0), tuple(4, 1), tuple(1, 100)])
+}