They uncovered one bug: in edit/003-shortcuts.mu
<scroll-down> was returning 0 for an address in one place where I
thought it was returning 0 for a boolean.
Now we've eliminated this bad interaction between tangling and punning
literals.
I've been working on this slowly over several weeks, but it's too hard
to support 0 as the null value for addresses. I constantly have to add
exceptions for scalar value corresponding to an address type (now
occupying 2 locations). The final straw is the test for 'reload':
x:num <- reload text
'reload' returns an address. But there's no way to know that for
arbitrary instructions.
New plan: let's put this off for a bit and first create support for
literals. Then use 'null' instead of '0' for addresses everywhere. Then
it'll be easy to just change what 'null' means.
Improvement on fix 3957: rather than put a band-aid over a slow
operation, eliminate the slowdown entirely.
In this case it turns out we're unnecessarily saving files to disk when
they could never be modified. Are we doing this on F4 as well?!
As a blanket rule, down-arrow now stops scrolling once the bottom margin
comes on screen.
Now that we have page-wise scrolling with ctrl-f/b and line-wise
scrolling with ctrl-s/x, we don't need to conflate scroll positioning
with the arrow keys. And as a result, early students no longer have to
struggle with accidentally scrolling part of the sandbox off the screen
when there's tons of empty space available.
`move-to-next-line` is still super messy and will need further
rethinking, but this commit simplifies the codebase as a whole by
eliminating a couple of historical accidents:
a) We only introduced scrolling past the bottom of the screen to allow
more sandboxes to come into view before we had scrolling for the
sandbox side.
b) We undid scrolling past the bottom in just the recipe side to allow
errors to come into view.
Since these historical details are now irrelevant, we no longer need
separate logic for the recipe and sandbox sides, and we don't need to
keep track of the recipe-bottom separate from the bottom margin of
arbitrary editors.
Redo cursor-down to fix a bug.
This should be the final bug I find as part of my audit of everywhere we
compare characters to newlines in layer 3 of the edit/ app.
Pretty messy implementation, but we'll clean it up now.
No, my conclusion in the previous commit was wrong. When you print a
character on the right margin, the cursor coordinates always wrap around
to the left margin on the next row. It's just that if you're at the
bottom of the screen, scrolling gives the impression that the row didn't
change.
Even though the bug of commit 3938 is now fixed, I'm still trying to
track down why the failure looked different on the fake screen than on
the real one. Snapshot as I try to track down the difference.
One key lesson is that the approach of commit 3860 -- updating the
cursor before rather than after printing each character -- turns out to
be untenable. A sequence of `print` followed by `cursor-position` needs
to behave the same as the real screen.
But it's still not clear how the real screen. When you get to the end of
a line the cursor position wraps after print to the left margin (column
0) on the next row. When you get to the bottom right the cursor position
wraps to the *bottom left* margin. How the heck does it know to scroll
on the next print, then? Is there some hidden state in the terminal?
Bugfix: when you hit `enter`, the cursor-row does not increment in *one*
special situation: when the line wraps and the cursor is right at the
start of one of the wrapped lines.
Kartik Agaram