So, this is what we need to modify to implement blocking code. We invent a new Javascript class that a function can return, to say “hey, I’m returning, but I’m not done yet; I’ve just blocked”. We call this a suspension.

So, when we’re compiling the AST, wherever we’re compiling a function call, we generate Javascript code that calls the function, and looks at the return value, and says, "is it a Suspension?". Because if it returned a Suspension, we’re blocking - and I'm going to have to suspend myself. We save all our variables and temporary values, our exception state, and where we are in the function, and then we return our own suspension with all that information in it.