fn: add basic generic queue

fn/queue.go

@@ -0,0 +1,51 @@
+package fn
+
+// Queue is a generic queue implementation.
+type Queue[T any] struct {
+	items []T
+}
+
+// NewQueue creates a new Queue.
+func NewQueue[T any](startingItems ...T) Queue[T] {
+	return Queue[T]{
+		items: startingItems,
+	}
+}
+
+// Enqueue adds one or more an items to the end of the Queue.
+func (q *Queue[T]) Enqueue(value ...T) {
+	q.items = append(q.items, value...)
+}
+
+// Dequeue removes an element from the front of the Queue. If there're no items
+// in the queue, then None is returned.
+func (q *Queue[T]) Dequeue() Option[T] {
+	if len(q.items) == 0 {
+		return None[T]()
+	}
+
+	value := q.items[0]
+	q.items = q.items[1:]
+
+	return Some(value)
+}
+
+// Peek returns the first item in the queue without removing it. If the queue
+// is empty, then None is returned.
+func (q *Queue[T]) Peek() Option[T] {
+	if q.IsEmpty() {
+		return None[T]()
+	}
+
+	return Some(q.items[0])
+}
+
+// IsEmpty returns true if the Queue is empty
+func (q *Queue[T]) IsEmpty() bool {
+	return len(q.items) == 0
+}
+
+// Size returns the number of items in the Queue
+func (q *Queue[T]) Size() int {
+	return len(q.items)
+}