<function> throws "Operator tuple not implemented" when a math child sits beside a multi-valued child

[dqnykamp]

Summary

A <function> that has a <math> child alongside a child expanding to more than one
value fails to build outright:

Operator tuple not implemented for conversion to mathjs

Nothing renders — the whole document dies, not just the function.

Reproductions

All of these throw:

<function><math>1</math><numberList>3 1 2</numberList></function>
<function><math>1</math><mathList>3 1 2</mathList></function>
<function><math>1</math><sequence to="3" /></function>
<function><math>1</math><sort>3 1 2</sort></function>
<function><math>1</math><shuffle>1 2 3</shuffle></function>
<function><math>1</math><repeat for="1 2" valueName="v">$v</repeat></function>
<function><math>1</math><conditionalContent><sort>3 1 2</sort></conditionalContent></function>
<function><math>1</math><group><numberList>3 1 2</numberList></group></function>

These are fine, which is what makes the failure surprising:

<function><math>1</math><number>3</number></function>
<function><math>1</math><number>3</number><number>1</number><number>2</number></function>
<function><math>1</math><math>1</math><math>2</math></function>
<function><math>1</math><group><number>3</number><number>1</number></group></function>
<function><math>1</math><repeat for="1" valueName="v">$v</repeat></function>
<function><numberList>3 1 2</numberList></function>

So it is not the number of children, and it is not composites as such. Writing the same
values out one component at a time works; routing them through anything that delivers
them as a single multi-valued child does not — and adding a second, single-valued <math>
child is what turns it from working into throwing.

Why it matters

The editor accepts every one of the throwing documents. <numberList>, <mathList>,
<sequence> and <conditionalContent> have always been legal children of <function>,
so this is not new, but nothing warns the author before the activity goes blank.

Notes

Found while sweeping every newly legal (container, composite) pair for
#1872. That PR makes <sort>, <shuffle>,
<repeat> and <repeatForSequence> legal children of <function> as well, which adds
four more spellings of the same crash but does not cause it — the <numberList> and
<conditionalContent> spellings above reproduce it on main.

Related: #1873, #1874, #1875 — other containers that mishandle a child they cannot
inspect before it expands.

🤖 Generated with Claude Code