Ruled 2026-10-04: guard all errors. The errors that set NODE-ERROR and
let the line run on now stop it at once, with a message.
- A store of a non-zero code to NODE-ERROR is a trap, a sixth kind of
fault: nothing after it executes, the return stack is emptied, and the
data stack is left as the word left it. Not attached, NODE-ERROR is
plain memory, as the tests below the prompt use it.
- The capsule's words store a code where they stored -1, and the prompt's
(RAISED) prints its message: Negative count, Not a number, Number too
long, Not a character, Dictionary full, Name missing, Control structure
mismatch, Control structures too deep.
- ' and COMPILE and [COMPILE] of a word that is not there say
UNKNOWN WORD: 'xxx', as the interpreter does.
- tests: the trap in test_exec.c; every message from the prompt, with the
rest of the line not run and the stack kept, in test_host_quit.c.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
With the stacks counted and guarded (D-16) their size is a parameter of
the node. The host node, which runs the interpreter and the compiler
under the user's programme, gets 32 values and 32 return entries; a mesh
node keeps the F18's 10 and 9. Nothing else about the mechanism or any
word's definition changes.
- stack.h: V4_DATA_RING and V4_RET_RING are build parameters; the
Makefile sets them for the host-node tests.
- tests/test_host_quit.c no longer assumes a size: it fills the stacks to
whatever they are, and takes every exit with the return stack full.
- Measured on the host node now: 28 values on a line, 29 waiting between
lines, words 31 deep from the prompt.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Ruled 2026-10-04, revising D-2: stack overflow and underflow are errors
that are shown and return to the prompt, not silent wrap-around.
- Each stack counts what it holds. Before every opcode the executor
checks that the stacks hold what it takes and have room for what it
leaves; otherwise the opcode does nothing and the node faults, as for a
bad address, to that kind's handler. Every fault empties both stacks.
- The fault handler is now a table of five jumps: address, data overflow,
data underflow, return overflow, return underflow. The host node says
"Stack overflow", "Stack underflow", "Return stack overflow",
"Return stack underflow", then ERROR and the prompt.
- Two registers, DSTACK-DEPTH and RSTACK-DEPTH: a fetch reads the depth,
a store empties the stack. QUIT, ABORT and the error exits empty the
return stack before they call anything; ABORT empties the data stack.
- capsule/forth.v4: DEPTH, PICK and ROLL, to FORTH-79 (counting from
one). PICK and ROLL set the values above the one wanted aside in
memory, and work with the stack full.
- Division by zero now takes its operands off the stack, as v3 does.
- A colon with no room for its entry abandons the line.
- tests: every opcode at every depth of both stacks; the faults, the
registers and the three words from the prompt.
The sizes are unchanged: ten values, nine return entries.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Layer 5 of the compiler capsule. The host node is now started at QUIT and
left running: it prompts, reads a line from its console with QUERY,
interprets it, says " ok" or " ERROR", and goes round again.
- capsule/quit.v4: QUIT and ABORT (FORTH-79), ABORT" and (ABORT") as v3 has
them, ." and (.") (FORTH-79). Text is compiled as a counted string after
the call; the run-time word returns to the cell after it.
- INTERPRET prints v3's messages before abandoning a line:
UNKNOWN WORD: 'xxx' and xxx: compile-only.
- core.v4: CR SPACE COUNT TYPE, as DECOMPOSITION.md gives them.
- input.v4: WORD split so that (PARSE) can take text without skipping
leading delimiters (." " is an empty string); EXPECT keeps its place in
memory, so six values may wait on the stack while a line is typed.
- tests/test_host_quit.c: the node is fed characters and its output read;
16 sessions are transcripts of the v3 binary.
QUIT stops the line from inside any word and says nothing; v3's goes on
with the line and cannot be compiled. v3's compiled ABORT" crashes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Measured, compiling a DO loop left one return entry spare under
INTERPRET and a defining word called from inside another word
overflowed the nine-entry return stack (D-2); the prompt loop will take
one more.
C@ and C! shift without a loop. The code generator shifts each opcode
into the word being built, so nothing is placed by a counted shift, and
the address masks come from a table. The dictionary search, the
in-liner, the end of a loop and the making of a data word are each one
word reached by a jump.
Every kind of line now leaves at least three return entries spare while
it compiles; a word run from the interpreter has six; and CREATE ...
DOES> works from the prompt, from a word, and from a word that calls
that.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The fourth layer of the compiler capsule. compile.v4: INTERPRET's
loop, STATE [ ] : ; EXIT IMMEDIATE LITERAL COMPILE [COMPILE] ' EXECUTE,
CREATE VARIABLE CONSTANT DOES>, and IF ELSE THEN BEGIN UNTIL AGAIN
WHILE REPEAT DO ?DO LOOP +LOOP on a control-flow stack in memory.
forth.v4: the first words of the vocabulary, the in-line ones.
FORTH source now goes in and running code comes out. 49 programmes
were run through the v3 binary and through this; every result agrees,
bar COMPILE, which v3 cannot run. The code laid down for each control
structure is word for word the expansion DECOMPOSITION.md gives.
A line may have six values on the stack while it is interpreted, and
words called from the interpreter may nest eight deep.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
