Rename cells containing screens to screen vars because of the ambiguity
that each grapheme in fake screens is represented by a type screen-cell.
While we're at it, we also analogously rename keyboard vars.
After all that, I'm not sure this is the desired behavior. If a function
defines multiple bindings, we shouldn't rename all their keys. So how to
choose?
Perhaps it's not so bad to have "symlinks" in this "file system". To unlink
two bindings you now need to define one of them in the sandbox.
All the refactoring is still useful, though.
It turns out there's another problem, and it predates the ability to create
new definitions:
ctrl-s triggers a call to `evaluate`, which inserts a new definition
into globals. which has a null gap buffer.
All this happens long before the new code in this commit, resulting in a
null gap buffer by the time we get to word-at-cursor.
Which in turn happens because we perform a raw `evaluate`, which doesn't
update the gap buffer like `run` does (using `maybe-stash-gap-buffer-to-global`).
And arguably `evaluate` shouldn't mess with the gap buffer. Gap buffers
are a UI concern.
The hardest version of this immediate scenario: It's unclear how to guarantee
that every definition have a gap buffer, when two definitions may share
one (closures sharing a lexical environment).
New plan:
- improve the logic for detecting definitions. Looking at the outermost
layer isn't enough. And a single expression can create multiple definitions.
- extract a helper to attach a single gap buffer to multiple definitions.
- have the UI detect conflicts in gap buffers and prompt the user for
a decision if a different gap buffer already exists for a definition.
I wrote a comment about how some code was not covered by tests, and then
promptly forgot what it was for. This is why we need tests.
Now the hack is gone.
