Three different things used to do this job, and which one you got depended on
where the machine was running. On a terminal the host held the line and did the
echoing and the backspacing; behind a window the console's own gatherer did it;
from a file nothing did it at all. One job, three implementations, none of them
in the system - which is why there was no way to move about in a line and
nowhere for a history to live.
So editLine does it. Key mode while a line is being read and line mode straight
after, so nothing else in the system and no program calling osReadLine notices
anything changed. Left and Right, Home and End, Backspace for the character
before the cursor and Delete for the one under it, and anything typed goes in
where the cursor is with the rest of the line moving along.
Ctrl-D means the end of input again, on an empty line, because that was a thing
the terminal did while it was holding the line and it is not holding it now.
Same trade as the echoing.
MOST KEYSTROKES DRAW NOTHING BUT THEMSELVES. A character typed at the end of a
line needs no cursor moved: printing it is the whole change, and a backspace
there is three ordinary bytes. That matters beyond speed - moving the cursor by
hand is what a terminal is TOLD about, in an escape sequence, so redrawing on
every keypress would fill every recorded transcript in this suite with them.
The line is only reprinted when something happened in the middle of it.
Where the line STARTS is worked out backwards from where printing ended, rather
than trusted from what was remembered. That is what makes it survive the screen
scrolling: a line printed on the bottom row moves everything up by one, and a
remembered row would be one too low from then on.
The command line holds 127 characters, up from 63. The limit started to be felt
the moment a line could be moved about in.
58 recordings changed, and every one of them by the echo. THE PROOF IS NOT A
HEURISTIC: a CosmOS built with the echo silenced reproduces 187 of the 188
recordings byte for byte. The one exception is cosmosTyped, the backspace test,
where the rub-out marks now come from the shell instead of from the console's
gatherer - same marks, different author.
cosmosEditKeys is the new test, and every line in it is typed wrong and then
corrected with a different key. Its last line is eighty six characters at a
prompt in column two on an eighty column screen, so the line runs onto the row
below and the shell has to find the start of something it can no longer see;
breaking either half of that arithmetic fails it.
Also: agree.sh looked for "> the same", anchored to a prompt that no longer
precedes what a command prints.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
A program that owns the whole machine had nowhere to run. It cannot be
started from the shell, because starting it means there is no shell, and
pointing boot.cfg at it means a machine that keeps starting it - which is a
poor place to find a mistake in something written five minutes ago.
Once writes /System/Boot/once.cfg, in the same format as boot.cfg and read
with the same routines, because a second format for one setting would be a
second format. The loader reads it before boot.cfg and DELETES IT BEFORE IT
JUMPS, which is the only moment there is: after the jump the loader does
not exist.
Consumed by being read rather than by working, so a one shot that hangs
cannot hang twice - the request is gone before the image ran, and the next
start reads boot.cfg like any other.
THE BOOT STATE IS NOT TOUCHED, and the first version got that wrong. It
marked the start the way any other start is marked, and then every
successful bare metal boot reported that it had never arrived - because a
program with the whole machine has no filesystem to clear a mark with and
is doing nothing wrong by not having one. Found by running it: the image
printed its line and the next start still said the last one did not.
Three disks, each a start further along, so none of the tests depends on
another having run.
The loop is closed on the machine now: write it in Edit, assemble it with
Asm, ask for it with Once, restart, watch it own the machine, and the
system comes back without being asked.
AnachronautandClaude Opus 5