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Let a script run a script, four deep

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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
This commit is contained in:
Anachronaut
2026-08-30 16:22:09 -04:00
co-authored by Claude Opus 5
parent a12d61fb80
commit c28826df77
10 changed files with 234 additions and 14 deletions
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Programs/CosmOS/Source/script.asm
+144 -5
View File
@@ -4,6 +4,7 @@
; CALL scriptOpen Q = 0 and a script is running, or Q says what was wrong:
; 1 there is no such file
; 2 it is not a script - no #! on the front
; 3 too many scripts inside each other
; DP0 = a buffer, B = how much room
; CALL scriptLine Q = 0 and there is a line in the buffer, or nonzero at the end
;
@@ -31,6 +32,87 @@
#Program
; ---- One script inside another ----
;
; A build script calling a setup script is the first thing anybody tries, so what is saved
; when one script starts another is a POSITION AND NOT A BUFFER. The whole state of a
; running script is its name, which block comes next, how many are left, and where in the
; block it is - seventy bytes, laid out next to each other below so that saving it 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.
;
; Four levels. Deep enough for a script calling a script that calls a helper, and shallow
; enough that a script which runs itself says so instead of filling memory.
scriptPush:
CALL scriptSlotAt
SETD.0 ScriptName
PSHD.3
POPD.1
CALL scriptCopyState
RET
scriptPop:
CALL scriptSlotAt
PSHD.3
POPD.0
SETD.1 ScriptName
CALL scriptCopyState
; ScriptAt points into the block buffer, which now holds somebody else's block. Reading
; it back is what makes the saved pointer mean what it meant.
CALL scriptReread
RET
; DP3 = where the script one level up is remembered. Reached by stepping rather than by
; multiplying, because this machine cannot multiply and the depth is never more than three
; steps. DP3 because RET puts the others back.
scriptSlotAt:
SETD.3 ScriptSaved
SETD.2 ScriptDepth
LDA.2
DECA
BRA scriptSlotDone
scriptSlotStep:
DPUP.3 0d70
DECA
BNA scriptSlotStep
scriptSlotDone:
RET
; Seventy bytes, DP0 to DP1.
scriptCopyState:
INIB 0d70
scriptCopyByte:
LDA.0
STA.1
INCD.0
INCD.1
DECB
BNB scriptCopyByte
RET
; The block that is meant to be in the buffer, back in the buffer. ScriptIndex is the NEXT
; one, so the one being read from is the one before it.
scriptReread:
SETD.1 ScriptIndex
LDA.1
INCD.1
LDB.1
DECB
BNC scriptRereadGo
DECA
scriptRereadGo:
SETD.0 ScriptName
SETD.1 ScriptBlock
SWI osFileBlock
SETD.1 ScriptBlock
PSHD.3
POPB
POPA
DPUW.1
RSTA
STA.1
RET
; ---- Opening ----
;
; The name is COPIED rather than remembered by address. osFileBlock is given the name again
@@ -39,6 +121,25 @@
; must stay valid; here it cannot, because the thing that reads the next line is the reason
; the name is needed.
scriptOpen:
; ---- Four deep and no further ----
SETD.1 ScriptDepth
LDA.1
INIB 0d4
CCF
SUB
BRQ scriptOpenTooDeep
; ---- The one already running is put somewhere safe FIRST ----
;
; Before anything below overwrites it, and put back again on every way out of here that is
; not success. Opening writes the name into the live state to ask the disk about it, so by
; the time the answer is known the caller's place is already gone.
;
; A still holds the depth from the check above: SUB writes Q and leaves it alone.
BRA scriptOpenFirst
CALL scriptPush
scriptOpenFirst:
SETD.1 ScriptName
INIB 0d63
CALL copyText
@@ -92,15 +193,29 @@ scriptOpenThere:
; Past the shebang line, wherever it ends.
CALL scriptSkipLine
INIA 0x01
SETD.1 ScriptRunning
SETD.1 ScriptDepth
LDA.1
INCA
STA.1
RSTA
BRI scriptOpenFailed ; A is nought, which is the answer for "it opened".
BRI scriptOpenAnswer ; A is nought, which is the answer for "it opened".
scriptOpenTooDeep:
INIA 0x03
BRI scriptOpenAnswer ; Nothing was pushed, so there is nothing to put back.
scriptOpenNotOne:
INIA 0x02
scriptOpenFailed:
; Whatever was running is still running, and its place is in the slot rather than in the
; live state. A is the answer and must survive being put back.
SETD.1 ScriptDepth
LDB.1
BRB scriptOpenAnswer
PSHA
CALL scriptPop
POPA
scriptOpenAnswer:
; Q is the answer, and A holds it. Adding nought is how a register becomes Q.
RSTB
CCF
@@ -322,16 +437,35 @@ scriptSkipLine:
scriptSkipDone:
RET
; One script ending. Whatever asked for it carries on, if anything did.
scriptClose:
SETD.1 ScriptDepth
LDA.1
BRA scriptCloseNone
DECA
STA.1
BRA scriptCloseNone
CALL scriptPop
scriptCloseNone:
RET
; Every script ending at once, which is what a line that did not work means. A build whose
; helper failed should not carry on in the script that called the helper either.
scriptAbandon:
RSTA
SETD.1 ScriptRunning
SETD.1 ScriptDepth
STA.1
RET
#Data
ScriptRunning:
ScriptDepth:
0x00
; ---- Seventy bytes, and they are next to each other on purpose ----
;
; Name, blocks left, next block, where in the block: the whole of where a script has got to.
; Saving it is one copy because of this order, and nothing else may be put between them.
ScriptName:
#Reserve 0d64
ScriptBlocks:
@@ -340,6 +474,11 @@ ScriptIndex:
0x00 0x00
ScriptAt:
0x00 0x00
; Three would do - a save happens on the second script and not the first - but four costs
; seventy bytes and removes an off-by-one from the only place it could hide.
ScriptSaved:
#Reserve 0d280
ScriptInto:
0x00 0x00
ScriptRoom: