It took me _way_ too long to realize that I'm not checking for errors within
the loop, and that will cause it to manifest as an infinite loop as inner
evaluations fail to run.
Debugging notes, for posterity:
printing one row of a chessboard pattern over fake screen (chessboard screen 4 0 0 15) gets stuck in an infinite loop halfway through
debug pattern during infinite loop: VWEX. It's still in the loop but it's not executing the body
raw (fill_rect screen 16 0 20 4 15) works fine
same number of calls to fill_rect work fine
replacing calls to fill_rect with pixel inside chessboard2 works fine
at the point of the infinite loop it's repeatedly going through the hline loop
-- BUT it never executes the check of the loop (< lo hi) with lo=20, hi=20. Something is returning 1, but it's not inside <
stream optimization is not implicated
simple test case with a single loop
(
(globals . (
(foo . (fn () (screen i n)
(while (< i n)
(pixel screen 4 4 i)
(pixel screen 5 4 i)
(pixel screen 6 4 i)
(pixel screen 7 4 i)
(set i (+ i 1)))))
))
(sandbox . (foo screen 0 100))
)
simpler (if you reset cursor position before every print):
(
(globals . (
(foo . (fn () (screen i n)
(while (< i n)
(print screen i)
(set i (+ i 1)))))
))
(sandbox . (foo screen 0 210))
)
I now believe it has nothing to do with the check. The check always works.
Sometimes no body is evaluated. And so the set has no effect.
All highly experimental. Current constraints:
* No tail recursion elimination
* No heap reuse
* Keep implementation simple
So it's slow, and I don't want to complicate it to speed it up. So I'm
investing in affordances to help deal with the slowness. However, in the
process I've taken the clean abstraction of a trace ("all you need to do
is add to the trace") and bolted on call counts and debug-prints as independent
mechanisms.
We now have a couple of protections:
- if we get close to running out of space in the trace we drop in an
error
- if we run out of space in the trace we stop trying to append
- if there are errors we cancel future evaluations
This is already much nicer. You can't do much on the Mu computer, but at
least it gracefully gives up and shows its limitations. On my computer
the Mu shell tries to run computations for about 20s before giving up.
That seems at the outer limit of what interactivity supports. If things
take too long, test smaller chunks.
I tried building a function to draw a horizontal line across the screen.
Here's what I have in data.txt:
(
(globals . (
(horline . (fn () (screen y)
(horline_1 screen y 0 (width screen))))
(horline_1 . (fn () (screen y lo hi)
(if (>= lo hi)
()
((fn ()
(pixel screen lo y 12)
(horline_1 screen y (+ lo 1) hi))))))
))
(sandbox . (horline_1 screen 0 0 20))
)
$ dd if=/dev/zero of=data.img count=20160
$ cat data.txt |dd of=data.img conv=notrunc
$ ./translate shell/*.mu && qemu-system-i386 -hda disk.img -hdb data.img
Result: I can't call (horline screen 0) over a fake screen of width 40.
Some stream overflows somewhere after all the tweaks to various fixed-size
buffers scattered throughout the app. Calling horline_1 gets to a 'hi'
column of 20, but not to 30.
Kartik K. Agaram