I've wrestled for a long time with how to support integer division with
its hard-coded registers. The answer's always been staring me in the face:
just turn it into a function! We already expect function outputs to go
to hard-coded registers.
Minor tweaks to get Mu shell running nicely on a Linux console atop Qemu.
We also need to switch a few 256-color codes to 8-color mode. I'm not
sure whether/how to patch the repo for those.
Both manual tests described in commit 7222 now work.
To make them work I had to figure out how to copy a file. It
requires a dependency on a new syscall: lseek.
Ok, I found a failing manual test for files as well.
Here are the two steelman tests, one for screens and one for files:
1.
5 5 fake-screen =s
s 1 down 1 right
ctrl-d foo
expand
final state:
s foo foo
s 1 down 1 right ⇗
┌─────┐ ┌─────┐
┌─────┐ 1 ┌─────┐ 1 ┌─────┐ │
┌─────┐ │ ┌─────┐ │ ─
│ │
│ │
─
└─────┘ └─────┘
└─────┘ └─────┘ └─────┘
└─────┘ └─────┘
2.
"x" open =f
f read f read
ctrl-d read2
expand
final state:
f read2 read2
f read f read ⇗
FILE ❝def❞
FILE ❝abc❞ FILE ❝❞
❝def❞ ❝ghi❞
In both cases there are 3 levels of issues:
- getting a single-line expression to work
- getting a single-line expression to work when operating on a binding
defined in a previous line
- getting an expanded function call to work
The third is where the rub is right now. And what both examples above share
is that the function performs 2 mutations to the screen/file.
So we need a deep copy after all. And it's not very clear how to copy a
file descriptor including the seek location. Linux's dup() syscall creates
an alias to the file descriptor. And opening /proc seems awfully Linux-specific:
https://stackoverflow.com/questions/54727231/duplicating-file-descriptor-and-seeking-through-both-of-them-independently/54727424#54727424
Even this isn't enough. While shallow copies keep us from transferring
new bindings to callers, the screen object is still the same, so mutations
to bindings are contagious.
Basically I'm losing IQ points from programming in a language that encourages
mutation over copying.
This bug was incredibly painful to track down: the one-line fix is to replace
'line' with 'first-line' in the call to 'evaluate' in render-line before
recursing.
Things that made it challenging:
- A high degree of coiling with recursive calls and multiple places of
evaluation.
- An accidental aliasing in bindings (when rendering the main column in
render-line) that masked the underlying bug and made things seem to work
most of the time.
- Too many fucking arguments to render-line, a maze of twisty line objects
all alike.
Attempt #3: always create a copy of the bindings before each column/evaluate.
The details are fuzzy in my head, but it seemed worth trying. I figured
I'd either see the old duplication behavior or everything will work. Instead
I'm seeing new problems.
commit 7208:
5 5 fake-screen =s
s 1 down 1 right
expected:
|
-
observed:
|
|
-
commit 7210-7212:
5 5 fake-screen =s
s 1 down 1 right
[define foo]
s foo
[expand foo]
observed: no bindings available when rendering foo expanded
commit 7213:
5 5 fake-screen =s
s 1 down 1 right
[define foo]
s foo
[expand foo]
expected within foo:
|
-
observed within foo:
|
|
-
commit 7215:
5 5 fake-screen =s
s 1 down 1 right
[define foo]
s foo
[expand foo]
observed: no bindings available when rendering foo expanded
Turns out even that doesn't work.
There are two distinct use cases here:
1. Keeping columns from infecting each other.
2. Expanding function calls.
Perhaps ping-ponging between them is a sign I need tests.
It turns out deciding when to initialize the table of bindings is quite
a thorny problem in the presence of function calls (since they need their
args bound). In time I should probably support a linked list of tables.
For now I'll just continue to reuse tables, but perform lookups in reverse
order so that the correct binding is always returned.
Kartik Agaram