Getting an unset variable

Usage Questions
1

Trash (now anti BLANK!) has been established as the value of unset variables. As the example in that thread states:

>> trash-value
** Error: TRASH-VALUE variable is unset

>> append [a b] get/any 'trash-value
** Error: APPEND does not allow adding ~ antiforms to blocks

But when I try this, I get quite different results:

>> trash-value
** Script Error: trash-value word is attached to a context, but unassigned

>> append [a b] get/any 'trash-value
** Script Error: trash-value word is not bound to a context

In fact, even GET/ANY doesn’t seem to work… even when I make sure the binding is right:

>> get/any 'trash-value
** Script Error: trash-value word is not bound to a context

>> get/any $trash-value             
** Script Error: trash-value word is attached to a context, but unassigned

So, what’s happening here? And how do I get trash out of an unset variable?

2

You're hitting a modern issue of "attachment binding":

Caching Binding Lookup, and "Attachment Binding"

Today's attached variables aren't unset, they don't exist at all.

It's possible to not draw a distinction in the UI, and treat these as existing but unset... but I suspect that's not a good thing to do.

But really, attachment binding is kind of dodgy. Better ideas are welcome.

3

What’s wrong with that? To me it seems the most logical approach. If I mention a variable which has never been set, I’d expect it to behave as if it were unset.

4

Attachment binding is just something that had to be done in order to get the system to boot under new binding rules. I don't have a coherent theory for it.

As such, I can't offhand immediately name "here's a thing that fundamentally doesn't work about equating attachment-bound things with being unset".

I can tell you that at least for my sake in debugging things, I like to know the difference.

But more generally, I can tell you that attachment binding is dodgy. If you try to pretend attachment-bound things are real variables that are backed by a memory location, then you'll be lying when you answer various questions like BINDING OF (not a great question to ask these days, crashes on things).

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