let_async.js

let let = macro {
    rule { async $vars  ... = $fname ... ($params ...); $rest ...} => {
        $fname ... ($params ..., function (err, $vars ...) { 
            if (err) throw err;
            $rest ... 
        })
    }
}

var buffer = new Buffer(1024);

let async infile = fs.open("/tmp/in.txt");
let async outfile = fs.open("/tmp/out.txt");
let async bytesRead, buffer = fs.read(infile, buffer, 0, 1024, 0);
let async bytesWritten, buffer = fs.write(outfile, buffer, 0, 1024, 0);
console.log("We read " + bytesRead + " bytes and wrote " + bytesWritten + " bytes.");


// compiles to:

var buffer$188 = new Buffer(1024);
fs.open('/tmp/in.txt', function (err$190, infile$191) {
    if (err$190)
        throw err$190;
    fs.open('/tmp/out.txt', function (err$193, outfile$194) {
        if (err$193)
            throw err$193;
        fs.read(infile$191, buffer$188, 0, 1024, 0, function (err$196, bytesRead$197, buffer$188) {
            if (err$196)
                throw err$196;
            fs.write(outfile$194, buffer$188, 0, 1024, 0, function (err$200, bytesWritten$201, buffer$188) {
                if (err$200)
                    throw err$200;
                console.log('We read ' + bytesRead$197 + ' bytes and wrote ' + bytesWritten$201 + ' bytes.');
            });
        });
    });
});