suspend-next.jspp

// We introduce two new keywords:
// suspend - Creates "suspended" functions, which will make your asynchronous code "synchronous" while keeping your UI responsive
// next - A "return" keyword for suspended functions

// Exhibit A: sleep function, no return value
external setTimeout;

suspend void sleep(int ms) { // use the 'suspend' modifier
    setTimeout(void() {
        next; // we do not return a value
    }, ms);
}

player.moveLeft(5);
sleep(100);
player.moveUp(2);

// Exhibit B: Read a file, return a value
import System;
external require;
external fs = require("fs");

suspend string? readFile(string path) { // use 'suspend' again, but this time with a nullable 'string' return type
    fs.readFile(path, void(err, contents) {
        if (err) {
            Console.error(err);
            next null;
        }

        next contents; // 'next' is a 'return' statement for async code
    });
}

string? contents = readFile("/home/foo/bar.txt");

// You can use any error handling mechanism including:
// 1) nullable/existent types
// 2) boolean values
// 3) "out" parameters (a la C)
// 4) result types (e.g. via classes)
// 5) etc.

// Exhibit C: read a file (without nullable types, throw on error)

import System;
external require;
external fs = require("fs");

suspend string readFile(string path) { // return just 'string' instead of nullable 'string?'
    fs.readFile(path, void(err, contents) {
        if (err) {
            throw err; // I'm told by the team that 'throw' will "just work," even from inside callback code
        }
        
        next contents;
    });
}

string contents = readFile("/home/foo/bar.txt");
Console.trace(contents); // eeeeaaaasy

// Exhibit D: suspend-next is compatible with ECMAScript 6 Promises right out of the box

// JS:
async function foo() {
   return 1;
}

// JS++:
external foo;

suspend int wrapFoo() {
   foo().then(void(result) { // notice the callback has return type 'void'
       next result; // but 'next' applies to the outer 'wrapFoo' int return type
   });
}