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feat(v4.0.0): division by zero is guarded (D-15); division words in the capsule

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Ruled 2026-10-04: guarded, an error shown, back to the prompt.

- capsule/forth.v4: / MOD /MOD */ */MOD M/MOD, M* and S>D join the
  vocabulary.  Each dividing word tests its divisor first; zero prints
  v3's message ("/: Division by zero"), ends an open definition, prints
  ERROR and returns to the prompt from however deep.
- SM/REM here has UM/MOD written into it and keeps its signs in memory,
  and */MOD has M* written in, so that division can be used inside words
  that other words call: / from four words deep, */MOD from three.
- forth.v4 now loads after quit.v4, which the guard leaves through.
- tests: v3 transcripts for each message; /MOD, /, MOD and */MOD against
  C on every pair of edge values.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
rajames
2026-10-04 12:23:30 -04:00
co-authored by Claude Opus 5.5
parent b3d2d56d11
commit 361dcd1148
5 changed files with 156 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files
v4/tests/test_host_quit.c
+13 -1
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@@ -21,6 +21,7 @@
* - control words that do not match give ERROR alone; v3 names the word.
* - QUERY takes 80 characters (FORTH-79); v3's line is 255.
* - an address outside memory says so (D-14); v3 gives ERROR alone.
* - M/MOD by zero says so (D-15); v3 gives ERROR alone.
*/
#include "v4/text.h"
#include "v4/testcode.h"
@@ -146,7 +147,18 @@ static const transcript script[] = {
{ ": P .\" two spaces \" 124 EMIT ; P\n", " two spaces | ok\nok> ", 1 },
{ "65 EMIT CR 66 EMIT\n", "A\nB ok\nok> ", 1 },
{ ": E .\" \" 65 EMIT ; E\n", "A ok\nok> ", 1 },
{ "65 EMIT 1 0 / 66 EMIT\n67 EMIT\n", "A/: Division by zero\n ERROR\nok> C ok\nok> ", 1 },
{ "1 0 MOD\n", "MOD: Division by zero\n ERROR\nok> ", 1 },
{ "1 0 /MOD\n", "/MOD: Division by zero\n ERROR\nok> ", 1 },
{ "1 1 0 */\n", "*/: Division by zero\n ERROR\nok> ", 1 },
{ "1 1 0 */MOD\n", "*/MOD: Division by zero\n ERROR\nok> ", 1 },
{ ": T 1 0 / 65 EMIT ; T 66 EMIT\n67 EMIT\n", "/: Division by zero\n ERROR\nok> C ok\nok> ", 1 },
{ "0 0 /\n7 2 / 48 + EMIT\n", "/: Division by zero\n ERROR\nok> 3 ok\nok> ", 1 },
/* v4's own */
{ "1 0 0 M/MOD\n", "M/MOD: Division by zero\n ERROR\nok> ", 0 },
{ ": Z0 0 / ; : Z1 65 EMIT 9 Z0 66 EMIT ; Z1\n: Z2 1 IF [ 5 0 MOD ]\nZ2\n",
"A/: Division by zero\n ERROR\nok> MOD: Division by zero\n ERROR\nok> UNKNOWN WORD: 'Z2'\n ERROR\nok> ", 0 },
{ ": Z3 5 0 DO 9 3 I - / DROP LOOP 65 EMIT ; Z3\n66 EMIT\n", "/: Division by zero\n ERROR\nok> B ok\nok> ", 0 },
{ ": BAD 1 NOSUCH 2 ;\nBAD\n65 EMIT\n", "UNKNOWN WORD: 'NOSUCH'\n ERROR\nok> UNKNOWN WORD: 'BAD'\n ERROR\nok> A ok\nok> ", 0 },
{ "1 ABORT\" now\" 65 EMIT\n66 EMIT\n", "now\n ok\nok> B ok\nok> ", 0 },
{ ": B1 IF LOOP ;\n65 EMIT\n", " ERROR\nok> A ok\nok> ", 0 },
@@ -172,7 +184,7 @@ int main(void)
printf("v4 host prompt tests: V4_CELL_BITS=%d, V4_NODE_WORDS=%u\n", V4_CELL_BITS, (unsigned)V4_NODE_WORDS);
{
static const char *const files[] = { "core.v4", "input.v4", "dict.v4", "codegen.v4", "compile.v4", "forth.v4", "quit.v4" };
static const char *const files[] = { "core.v4", "input.v4", "dict.v4", "codegen.v4", "compile.v4", "quit.v4", "forth.v4" };
CHECK(host_load(&tx, &n, files, 7), "the capsule assembles");
}
CHECK(v4_text_finish(&tx), "everything is defined: %s", v4_text_error(&tx));