The problem seems to extend to functions where the return type is a Z1-typed list. From my comment on https://www.wikifunctions.org/view/en/Z16430, I assume that we used to get an unaltered list back, rather than the current errors.

For now, we don't support type conversion on untyped lists, or on functions that return a Z1. That's indeed a missing feature still.

In T370028#9987697, @DVrandecic wrote:

For now, we don't support type conversion on untyped lists, or on functions that return a Z1. That's indeed a missing feature still.

Okay, but now we can reverse (or find the last element of) an untyped list of integers, months… whatever, but we can’t reverse a typed list without creating a specific function for that type of list. Please see other examples at https://www.wikifunctions.org/wiki/Wikifunctions:Catalogue#Functions_with_list_outputs.

I think it would help here if we could have a function to convert a typed list into an untyped list, as a matter of priority. It does not appear to be possible to write such a function (note failing implementations for Z801 with test https://www.wikifunctions.org/view/en/Z17799).

Yes it does seem strange to me that https://www.wikifunctions.org/view/en/Z13725 works. So untyping lists could be a useful (but strange!) workaround.

@DVrandecic Just to be clear. It is TYPED lists that fail. UNTYPED (Z1) lists are fine.

In T370028#9988099, @GrounderUK wrote:

I think it would help here if we could have a function to convert a typed list into an untyped list, as a matter of priority. It does not appear to be possible to write such a function.

We have now created https://www.wikifunctions.org/view/en/Z17895, which exploits a loophole in Z973. This means we will not need a built-in implementation (or equivalent function), so long as Z973 continues to return a Z1-typed list.