A build script calling a setup script is the first thing anybody tries.
What is saved when one script starts another is A POSITION AND NOT A
BUFFER: the name, which block comes next, how many are left, and where in
the block it had got to. Seventy bytes, and they sit next to each other in
the data segment on purpose so that saving them is one copy. The block
itself is read again on the way back, which costs one disk read per return
and saves 257 bytes a level - the inner script reads its own block into the
single buffer there is, so coming back means fetching the outer one's block
again and landing on the byte it left.
The slot is reached by stepping rather than by multiplying, because this
machine has no multiply and the depth is never more than three steps.
Four levels. Deep enough for a script calling a script that calls a helper,
shallow enough that a script running itself says so rather than filling
memory. A line that fails now stops every level and not just the innermost,
because a build whose helper failed should not carry on in its caller.
The caller's place is saved BEFORE the new file is looked at, and put back
on every way out that is not success. Opening writes the name into the live
state in order to ask the disk about it, so by the time "there is no such
file" is known, the caller's place has already been overwritten - a failed
'do' inside a script would otherwise leave the script that ran it reading
from a name it never chose.
The test resumes in the outer script's SECOND block, which is the case the
whole design turns on and the one an ordinary nesting test would miss.
Breaking the re-read, the save, or the limit each fails it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
'do <file>' runs the lines in a file as though they had been typed. The
only thing a script changes is where the next line comes from: everything
below shellReadLine - splitting the line, matching it, loading a program -
cannot tell the difference and does not have to.
What makes a file a script is '#!' on the front of it, not its name and not
a flag in its entry. The rule this filesystem keeps is that an entry holds
only what the content cannot say about itself, and a script can say what it
is; the loader already refuses anything that is not SBEX, so the two kinds
of runnable file turn each other away without either knowing about the
other. It is also the deferred half of the file-typing design, which said
to wait for a second kind of runnable thing before building any of it. This
is that second kind.
'#' is a directive and ';' is a comment, as in SplitBit assembly - one rule
across the machine rather than two dialects. Not Unix's convention: there
'#!' really is a comment that only the kernel reads, while here the shell
requires it and refuses the file without it, so calling it a comment would
be a lie about what it does.
A script stops at the first line that does not work, which is what the
LineFailed groundwork was for. Comments and blank lines are dropped by the
reader rather than by the dispatch, so they are not echoed either. A script
running out hands back to the console rather than ending the shell, because
running out of file and running out of typing are not the same thing. The
interactive assembler reads through the same path, so a script can contain
a block of assembly.
Three things this cost that were not obvious:
- RET puts A and B back, so a routine cannot answer in them. scriptByte
returning the character in A assembled, ran, and handed the caller its
own A back every time. It answers in memory now.
- A last line with no newline is still a line. Text files do not reliably
end with one and an editor eating it is a bad way to find out a command
did not run.
- Not LastStatus. See the commit before this one.
Six checks in three tests, two of which are about byte positions rather
than behaviour - a command lying across the boundary between two blocks,
and that missing newline - so their fixtures are generated rather than
committed, where an editor cannot helpfully repair them.
Nesting is not in yet: a script cannot run a script. That wants a stack of
positions rather than the one the reader keeps.
Also derives native.sh's self-hosting source list from cosmos.asm's own
#Include lines. It was a hand written list and went stale the moment
script.asm existed - the fourth time a list beside a thing has drifted from
the thing - so it now asks the thing.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
AnachronautandClaude Opus 5