set.from_list

Author: lpil

CHANGELOG.md

@@ -5,8 +5,8 @@
 - Created the `iterator` module with the `unfold`, `repeatedly`, `repeat`,
   `from_list`, `fold`, `run`, `to_list`, `take`, `drop`, `map`, `filter`,
   `cycle`, and `range` functions.
-- Created the `set` module with the `new`, `insert`, `delete`, `to_list` and
-  `contains` functions.
+- Created the `set` module with the `new`, `insert`, `delete`, `to_list`,
+  `from_list` and `contains` functions.
 - Created the `io` module with the `print`, `println`, and `debug` functions.
 - Created the `queue` module with the `new`, `from_list`, `to_list`,
   `is_empty`, `length`, `push_back`, `push_front`, `pop_back`, `pop_front`,
@@ -27,6 +27,7 @@
 - The `list` module gains the `filter_map` function.
 - The `list.contains` label `has` has been changed to `any`.
 - The `list.sort` label `sort_by` has been changed to `by`.
+- The `list.fold`'s first argument gained the label `over`.
 
 ## v0.8.0 - 2020-04-28
 

src/gleam/list.gleam

@@ -426,7 +426,7 @@ pub fn flatten(lists: List(List(a))) -> List(a) {
 ///
 /// This function runs in linear time.
 ///
-pub fn fold(list: List(a), from initial: b, with fun: fn(a, b) -> b) -> b {
+pub fn fold(over list: List(a), from initial: b, with fun: fn(a, b) -> b) -> b {
   case list {
     [] -> initial
     [x, ..rest] -> fold(rest, fun(x, initial), fun)

src/gleam/set.gleam

@@ -1,5 +1,6 @@
 import gleam/map.{Map}
 import gleam/result
+import gleam/list
 
 /// A set is a collection of unique elements of the same type.
 ///
@@ -65,6 +66,8 @@ pub fn contains(in set: Set(element), this member: element) -> Bool {
 /// Remove an element from a set. If the set does not contain the element then
 /// the set is returned unchanged.
 ///
+/// This function runs in logarithmic time.
+///
 /// ## Examples
 ///
 ///    > new() |> insert(2) |> delete(2) |> contains(1)
@@ -79,6 +82,8 @@ pub fn delete(from set: Set(element), this member: element) -> Set(element) {
 /// The list has no specific ordering, any unintentional ordering may change in
 /// future versions of Gleam or Erlang.
 ///
+/// This function runs in linear time.
+///
 /// ## Examples
 ///
 ///    > new() |> insert(2) |> to_list
@@ -87,3 +92,22 @@ pub fn delete(from set: Set(element), this member: element) -> Set(element) {
 pub fn to_list(set: Set(element)) -> List(element) {
   map.keys(set.map)
 }
+
+/// Create a new set of the elements in a given list.
+///
+/// This function runs in loglinear time.
+///
+/// ## Examples
+///
+///    > import gleam/list
+///    > [1, 1, 2, 4, 3, 2] |> from_list |> to_list |> list.sort
+///    [1, 3, 3, 4]
+///
+pub fn from_list(elements: List(element)) -> Set(element) {
+  let map = list.fold(
+    over: elements,
+    from: map.new(),
+    with: fn(k, m) { map.insert(m, k, []) },
+  )
+  Set(map)
+}

test/gleam/set_test.gleam

@@ -50,3 +50,11 @@ pub fn to_list_test() {
   |> list.sort(by: int.compare)
   |> should.equal([2, 3, 4])
 }
+
+pub fn from_list_test() {
+  [1, 1, 2, 4, 3, 2]
+  |> set.from_list
+  |> set.to_list
+  |> list.sort(by: int.compare)
+  |> should.equal([1, 3, 3, 4])
+}