#5565 tcl_output of a list of lists prints SIMP or NIL before the values

[David Scherfgen]

This bug was discovered by Claude Opus 5.5 and reproduced on Maxima Git commit c62924c (2026-09-26) with SBCL 2.2.9.

Where: src/xmaxima_def.lisp, $TCL_OUTPUT

For a list of lists $TCL_OUTPUT loops over the whole Maxima list, including its header (MLIST SIMP), and prints element I of the header as well.

Steps

1. Verify that the existing behavior is incorrect: run the reproducer below; it gives the result under "Before the fix". Judge for yourself that this is wrong instead of relying on the ticket: where the bug allows it, try some related inputs of your own, or check the result another way, for example numerically or against the documentation.
2. Edit the files src/xmaxima_def.lisp, doc/info/Miscellaneous.texi as described under "Fix".
3. Rebuild Maxima.
4. Verify that the behavior is now correct: the reproducer gives the result under "Correct result". Judge for yourself that this is right, not only that it matches: where the bug allows it, try some related inputs of your own, including some that the fix should leave unchanged.
5. Add the test case(s) under "Test cases" to tests/rtest_plotoptions.mac, at the end of the file.
6. Run the complete test suite, share tests included (make check, or run_testsuite(share_tests=true); in ./maxima-local), and check that the change breaks no test. Failures that also occur without the change (a run on the unchanged build shows which) are pre-existing and can be ignored.
7. Add the line * \#5565 tcl_output of a list of lists prints SIMP or NIL before the values to ChangeLog, under "Bug fixes for numbered bugs:".
8. Commit the fix; a proposed Git commit message is under "Commit message".
9. Push the commit. Then set this ticket's status to "closed" and add a comment naming the commit, for example Fixed by commit [1a2b3c]., with the first six characters of the commit's SHA in the brackets (git rev-parse HEAD | cut -c1-6 prints them). SourceForge links this to the commit.

Reproducer

tcl_output([[1,2,3],[11,22,33]],1)$

Before the fix:

{SIMP 1. 11. }

Correct result:

{1. 11. }

Fix

In src/xmaxima_def.lisp ($TCL_OUTPUT, line "(loop for v in lis" after "(cond (($listp (second lis))"), replace

  (cond (($listp (second lis))
         (loop for v in lis

with

  (cond (($listp (second lis))
         (loop for v in (cdr lis)

Test cases

Add these lines to tests/rtest_plotoptions.mac, separated from the tests before them by two empty lines:

/* Bug #5565: "tcl_output of a list of lists prints SIMP or NIL before the values" */

block ([s: make_string_output_stream (), o],
  with_stdout (s, tcl_output ([[1, 2, 3], [11, 22, 33]], 1)),
  o: get_output_stream_string (s),
  [ssearch ("simp", o, 'sequalignore), integerp (ssearch ("11", o))]);
[false, true]$

Commit message

xmaxima_def.lisp: fix tcl_output of a list of lists

For a list of lists $TCL_OUTPUT looped over the whole Maxima list,
including its header, so it printed SIMP or NIL before the values. Skip
the header, and correct the example in the manual.

This fixes bug #5565.

Found and fixed by Claude Opus 5.5.