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.
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?
Hook up fake screen to scroll properly on cursor-down.
Thanks Lakshman Swaminathan for finding this hole in commit 3860 with your
incessant fidgeting :)
To achieve this we have to switch to a model of the screen in termbox that
is closer to the underlying terminal.
Before:
a screen is a grid of characters
writing out of bounds does nothing
After:
a screen is a scrolling raster of characters
writing out of bounds wraps to next line and scrolls if necessary
To move to the new model, it was essential that I migrate my fake screen
at the same time to mimic it. This is why the first attempt (commit 3824)
failed (commit 3858). This is also why this commit can't be split into
smaller pieces.
The fake screen now 'scrolls' by rotating screen lines from top to bottom.
There's still no notion of a scrollback buffer.
The newer model is richer; it permits repl-like apps that upstream termbox
can't do easily. It also permits us to simply use `printf` or `cout` to
write to the screen, and everything mostly works as you would expect. Exceptions:
a) '\n' won't do what you expect. You need to explicitly print both '\n'
and '\r'.
b) backspace won't do what you expect. It only moves the cursor back,
without erasing the previous character. It does not wrap.
Both behaviors exactly mimic my existing terminal's emulation of vt100.
The catch: it's easy to accidentally scroll in apps. Out-of-bounds prints
didn't matter before, but they're bugs now. To help track them down, use
the `save-top-idx`, `assert-no-scroll` pair of helpers.
An important trick is to wrap the cursor before rather after printing
a character. Otherwise we end up scrolling every time we print to the
bottom-right character. This means that the cursor position can be invalid
at the start of a print, and we need to handle that.
In the process we also lose the ability to hide and show the screen. We
have to show the prints happening. Seems apt for a "white-box" platform
like Mu.
Always start with an untouched screen that can scroll on printing "\r\n".
We can still clear the screen as needed.
Also drop support for hiding the cursor.
Now it's much more apparent why things are slow. You can see each repaint
happening. Already I fixed one performance bug -- in clear-rest-of-screen.
Since this subverts Mu's fake screen there may be bugs.
Another salubrious side effect: I've finally internalized that switching
to raw mode doesn't have to clear the screen. That was just an artifact
of how termbox abstracted operations. Now I can conceive of using termbox
to build a repl as well.
(I was inspired to poke into termbox internals by
http://viewsourcecode.org/snaptoken/kilo and
https://github.com/antirez/linenoise)
Periodic cleanup to replace 'reply' with 'return' everywhere in the
repo.
I use 'reply' for students to help reinforce the metaphor of function
calls as being like messages through a pipe. But that causes 'reply' to
get into my muscle memory when writing Mu code for myself, and I worry
that that makes Mu seem unnecessarily alien to anybody reading on
Github.
Perhaps I should just give it up? I'll try using 'return' with my next
student.
A long-standing problem has been that I couldn't spread code across
'run' blocks because they were separate scopes, so I've ended up making
them effectively comments. Running code inside a 'run' block is
identical in every way to simply running the code directly. The 'run'
block is merely a visual aid to separate setup from the component under
test.
In the process I've also standardized all Mu scenarios to always run in
a local scope, and only use (raw) numeric addresses for values they want
to check later.
Commit 3370 fixed the memory leak but it still had print:character
printing characters rather than numbers like it used to before 3365. Go
back to the old, unambiguous trace.
There's still a problem: if I ever want to use any of the special
scenario variables like 'screen', 'console', etc., then I can't use
'local-scope' in my scenario.
I'm dropping all mention of 'recipe' terminology from the Readme. That
way I hope to avoid further bike-shedding discussions while I very
slowly decide on the right terminology with my students.
I could be smarter in my error messages and use 'recipe' when code uses
it and 'function' otherwise. But what about other words like ingredient?
It would all add complexity that I'm not yet sure is worthwhile. But I
do want separate experiences for veteran programmers reading about Mu on
github and for people learning programming using Mu.
It also seems useful that the number maps to the name of the file the
sandbox is saved in. However this mapping is currently a happy accident
and not actually tested.
I'm starting to switch gears and help make the editor useable with
many many sandboxes. This is just the first step of several.
This is the one major refinement on the C programming model I'm planning
to introduce in mu. Instead of Rust's menagerie of pointer types and
static checking, I want to introduce just one new type, and use it to
perform ref-counting at runtime.
So far all we're doing is updating new's interface. The actual
ref-counting implementation is next.
One implication: I might sometimes need duplicate implementations for a
recipe with allocated vs vanilla addresses of the same type. So far it
seems I can get away with just always passing in allocated addresses;
the situations when you want to pass an unallocated address to a recipe
should be few and far between.
Still can't print non-integer numbers, so this is a bit hacky.
The big consequence is that you can't print literal characters anymore
because of our rules about how we pick which variant to statically
dispatch to. You have to save to a character variable first.
Maybe I can add an annotation to literals..
Not entirely happy with this. Maybe we'll find a better name. But at
least it's an improvement.
One part I *am* happy with is renaming string-replace to replace,
string-append to append, etc. Overdue, now that we have static dispatch.
Kartik Agaram