feat(stdlib): Added empty constant to immutable data structures (#1466)

feat(stdlib): Add `empty` constant to ImmutablePriorityQueue module
feat(stdlib): Add `empty` constant to Queue module
feat(stdlib): Add `empty` constant to Stack module

Author: alex-snezhko

compiler/test/stdlib/immutablepriorityqueue.test.gr

@@ -2,6 +2,8 @@ import ImmutablePriorityQueue from "immutablepriorityqueue"
 import List from "list"
 import Array from "array"
 
+assert ImmutablePriorityQueue.make(compare) == ImmutablePriorityQueue.empty
+
 // formatter-ignore
 let lotsOfVals = [>
   3, 2, 1, 5, 3, 2, 2, 10, 6, 5,

stdlib/immutablepriorityqueue.gr

@@ -41,9 +41,19 @@ record ImmutablePriorityQueue<a> {
 }
 
 /**
- * @section Values: Functions for working with ImmutablePriorityQueues.
+ * @section Values: Functions and constants for working with ImmutablePriorityQueues.
  */
 
+/**
+ * An empty priority queue with the default `compare` comparator.
+ * 
+ * @since v0.5.4
+ */
+export let empty = {
+  let empty = { comp: compare, size: 0, root: None }
+  empty
+}
+
 /**
  * Creates a new priority queue with a comparator function, which is used to
  * determine priority of elements. The comparator function takes two elements

stdlib/immutablepriorityqueue.md

@@ -27,7 +27,20 @@ Immutable data structure which maintains a priority order for its elements.
 
 ## Values
 
-Functions for working with ImmutablePriorityQueues.
+Functions and constants for working with ImmutablePriorityQueues.
+
+### ImmutablePriorityQueue.**empty**
+
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
+
+```grain
+empty : ImmutablePriorityQueue<a>
+```
+
+An empty priority queue with the default `compare` comparator.
 
 ### ImmutablePriorityQueue.**make**
 

stdlib/queue.gr

@@ -15,13 +15,26 @@ record Queue<a> {
 }
 
 /**
- * @section Values: Functions for working with queues.
+ * @section Values: Functions and constants for working with queues.
  */
 
+/**
+ * An empty queue.
+ * 
+ * @since v0.5.4
+ */
+export let empty = {
+  let empty = { forwards: [], backwards: [] }
+  empty
+}
+
 /**
  * Creates an empty queue.
  * 
  * @returns An empty queue
+ * 
+ * @deprecated This will be removed in the v0.6.0 release of Grain.
+ * 
  * @since v0.2.0
  */
 export let make = () => {

stdlib/queue.md

@@ -25,10 +25,25 @@ type Queue<a>
 
 ## Values
 
-Functions for working with queues.
+Functions and constants for working with queues.
+
+### Queue.**empty**
+
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
+
+```grain
+empty : Queue<a>
+```
+
+An empty queue.
 
 ### Queue.**make**
 
+> **Deprecated:** This will be removed in the v0.6.0 release of Grain.
+
 <details disabled>
 <summary tabindex="-1">Added in <code>0.2.0</code></summary>
 No other changes yet.

stdlib/stack.gr

@@ -20,10 +20,22 @@ record Stack<a> {
  * @section Values: Functions and constants included in the Stack module.
  */
 
+/**
+ * An empty stack.
+ * 
+ * @since v0.5.4
+ */
+export let empty = {
+  let empty = { data: [], }
+  empty
+}
+
 /**
  * Creates a new stack.
  *
  * @returns An empty stack
+ * 
+ * @deprecated This will be removed in the v0.6.0 release of Grain.
  */
 export let make = () => {
   { data: [], }

stdlib/stack.md

@@ -24,8 +24,23 @@ Stacks are immutable data structures that store their data in a List.
 
 Functions and constants included in the Stack module.
 
+### Stack.**empty**
+
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
+
+```grain
+empty : Stack<a>
+```
+
+An empty stack.
+
 ### Stack.**make**
 
+> **Deprecated:** This will be removed in the v0.6.0 release of Grain.
+
 ```grain
 make : () -> Stack<a>
 ```