add async support for the js backend, and some promise helpers (thank…

…s to @nschulzke), along with some samples.

examples/async/file-js.js

@@ -0,0 +1,13 @@
+import fs from 'fs';
+
+function readfile(f) {
+    return new Promise((resolve, reject) => {
+        return fs.readFile(f, 'utf8', (err, data) => {
+            if (err) {
+              reject(err);
+            }
+            resolve(data);
+        });
+    });
+}
+

examples/async/file-js.kk

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+import std/jsextern
+
+extern import
+  js file "file-js.js"
+
+extern ext/read-file(path: string): io-noexn any
+  js inline "readfile(#1)"
+
+fun js/read-file(path: string): <io,async> string
+  Jspromise(read-file(path)).wrap.unsafe-as-string
+
+fun main()
+  val res = try
+    js/read-file("examples/async/file-js.kk").println
+  ()

examples/async/timer.kk

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+import std/async
+import std/time/duration
+import std/time/timestamp
+
+fun main()
+  val res = try
+    val x = ref(0)
+    timer(1000.milli-seconds) fn(t)
+      "Hello From Timer".println
+      x := !x + 1
+      if !x == 3 then False else True
+    wait(1.seconds)
+    "Before timeout".println
+    wait(10.seconds)
+    "Hello After Timeout".println
+  println("Done!")
+

std/async.kk

@@ -0,0 +1,10 @@
+/*----------------------------------------------------------------------------
+   Copyright 2024, Koka-Community Authors
+
+   Licensed under the MIT License ("The License"). You may not
+   use this file except in compliance with the License. A copy of the License
+   can be found in the LICENSE file at the root of this distribution.
+----------------------------------------------------------------------------*/
+
+pub import std/async/async
+pub import std/async/timer