Array.fromSingleton

Author: jmagaram

src/Core__Array.res

@@ -245,3 +245,5 @@ let findMap = (arr, f) => {
 }
 
 @send external at: (array<'a>, int) => option<'a> = "at"
+
+@val external fromSingleton: 'a => array<'a> = "Array.of"

src/Core__Array.resi

@@ -969,3 +969,23 @@ let findMap: (array<'a>, 'a => option<'b>) => option<'b>
 */
 @send
 external at: (array<'a>, int) => option<'a> = "at"
+
+/**
+`fromSingleton` generates a new array from a single value.
+
+## Examples
+
+```rescript
+3->Array.fromSingleton // [3]
+undefined->Array.fromSingleton // [undefined]
+Some("abc")->Array.fromSingleton // [Some("abc")]
+{"x": 3, "y": 5}->Array.fromSingleton // Some({"x": 3, "y": 5})
+```
+
+## Specifications
+
+- [Array.of MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/of)
+- [Array.of ECMAScript Language Specification](https://tc39.es/ecma262/multipage/indexed-collections.html#sec-array.of)
+*/
+@val
+external fromSingleton: 'a => array<'a> = "Array.of"

test/ArrayTests.mjs

@@ -401,7 +401,66 @@ Test.run([
 
           })), eq, undefined);
 
+function singletonTest(a, title) {
+  Test.run([
+        [
+          "ArrayTests.res",
+          103,
+          22,
+          48
+        ],
+        "fromSingleton : " + title + ""
+      ], Array.of(a), Caml_obj.equal, [a]);
+  Test.run([
+        [
+          "ArrayTests.res",
+          104,
+          22,
+          48
+        ],
+        "fromSingleton : " + title + ""
+      ], Array.of(a).length, eq, 1);
+  Test.run([
+        [
+          "ArrayTests.res",
+          106,
+          15,
+          41
+        ],
+        "fromSingleton : " + title + ""
+      ], Array.of(a)[0], (function (i, j) {
+          return i === j;
+        }), a);
+}
+
+var m = Array.of({
+      x: 3,
+      y: 5
+    });
+
+singletonTest(3, "Single integer");
+
+singletonTest("abc", "Single string");
+
+singletonTest(undefined, "undefined");
+
+singletonTest(null, "null");
+
+singletonTest([
+      1,
+      2,
+      3
+    ], "full array of integers");
+
+singletonTest([], "empty array");
+
+singletonTest(5, "Some");
+
+singletonTest(undefined, "None");
+
 export {
   eq ,
+  singletonTest ,
+  m ,
 }
 /*  Not a pure module */

test/ArrayTests.res

@@ -98,3 +98,23 @@ Test.run(
   eq,
   None,
 )
+
+let singletonTest = (a, title) => {
+  Test.run(__POS_OF__(`fromSingleton : ${title}`), Array.fromSingleton(a), (i, j) => i == j, [a])
+  Test.run(__POS_OF__(`fromSingleton : ${title}`), Array.fromSingleton(a)->Array.length, eq, 1)
+  Test.run(
+    __POS_OF__(`fromSingleton : ${title}`),
+    Array.fromSingleton(a)->Array.getUnsafe(0),
+    (i, j) => i === j,
+    a,
+  )
+}
+let m = {"x": 3, "y": 5}->Array.fromSingleton
+3->singletonTest("Single integer")
+"abc"->singletonTest("Single string")
+undefined->singletonTest("undefined")
+null->singletonTest("null")
+[1, 2, 3]->singletonTest("full array of integers")
+[]->singletonTest("empty array")
+Some(5)->singletonTest("Some")
+None->singletonTest("None")

test/TestSuite.mjs

@@ -28,6 +28,10 @@ var Concurrently = PromiseTest.Concurrently;
 
 var panicTest = ErrorTests.panicTest;
 
+var singletonTest = ArrayTests.singletonTest;
+
+var m = ArrayTests.m;
+
 var $$catch = IntTests.$$catch;
 
 var forEachIfOkCallFunction = ResultTests.forEachIfOkCallFunction;
@@ -61,6 +65,8 @@ export {
   Catching ,
   Concurrently ,
   panicTest ,
+  singletonTest ,
+  m ,
   $$catch ,
   forEachIfOkCallFunction ,
   forEachIfErrorDoNotCallFunction ,