optional arguments cannot be initialised with async expressions

[refractalize]

Consider this:

n = 0

f! = ++n

o! (a: f!) = a

console.log (o!)
console.log (o!)

This compiles into something you wouldn't expect, that is, the definition of o is made after an asynchronous call to f, so the first invocation of o comes out as you'd expect with a result of 1, but the second also comes out as 1, whereas you'd expect it to run f again to yield a result of 2.