How it works is, anytime the compiler sees an undefined symbol, it creates a new box for it like as if it had been created with "var".
Another way to think about it is... the compiler would replace this:
(= foo (fn () ... bar ...))
(= bar (fn () ... foo ...))
With this:
(var bar)
(var foo)
(= foo (fn () ... bar ...))
(= bar (fn () ... foo ...))
What happened is, when it encountered the undefined variable "bar", it created a new box for it. Then it encountered the undefined variable "foo", so it created a new box for it. Then it did the assignments like normal.
Given how you said "compiling-a-reference-time", I think we're talking about the same thing. Why did you mention assignment time?
We've just had a long exchange about you creating boxes at assignment time and me using compiling-a-reference time instead. Here's a recap:
---
You: Here's how you do it. The definition of "=" is the same: if the variable exists, mutate it, otherwise create a new variable. But now you add in a new primitive called "var"[...]
Me: The behavior I'd use is that any compile-time variable access (even under a lambda) creates a new, uninitialized variable binding if a binding doesn't already exist.
You: Yeah I'd do that too, if I wanted to graft dynamic variables onto a hyper-static system. But since Arc uses dynamic variables, I proposed to graft hyper-static onto it instead.
Me: How do you make the even/odd code work? Under the approach you described, the first line refers to an undefined variable (odd), and I interpret that as an error. I was recommending a fix.
You: Easy: I have a macro called "defs" that handles mutual recursion
Me: While I appreciate 'defs, it's a non-answer. The even/odd example [...] should work without modification.
You: It will work in my system as well, because undefined symbols automatically create new boxes.
Ah, sorry, huge miscommunication and misunderstanding on my part. I've actually been agreeing with you all along.
A large part of the problem is that I've been thinking about my proposal as two separate parts: one part deals with backwards compat with Arc, and the other part describes a hyper-static system for Arc.
When I was talking about "defs", I was talking about the hyper-static part. But you were talking about the backwards compat part. Hilarity (?) ensues.
