I haven't been able to find a compelling example of a 4-D array.
There is a synthetic example of a 3-D array in the format-array
section.

On Sat, Apr 11, 2026 at 7:05 PM John Cowan <xxxxxx@ccil.org> wrote:
>
> On Sat, Apr 11, 2026 at 9:42 AM Peter McGoron <xxxxxx@mcgoron.com> wrote:
>
> > Would it be better to have the single integer be the lower bound, and
> > have the upper bound be determined by the length of the array?
>
> I think that would be quite surprising. I did a little cross-language
> investigation, and few languages support lower bounds at all despite
> their obvious utility: Fortran, PL/I, ANSI Full Basic, and Algol 60
> and 68.  In the Algols, the lower bound is always required: otherwise
> a single bound is taken to be the upper bound.  (Many Basics only
> allow the lower bound of all dimensions of all arrays to be set
> globally with the "Option Base 0|1" statement.)
>
> > It would
> > be easier to modify the array without having to count the number of
> > elements in each dimension
>
> That's true, and it was one of the reasons why I originally went with
> just having lower bounds.  But I think their ergonomics are terrible.
> You should be able to determine the shape of an array without looking
> at the data in it.
>
> > I can do so without modifying the type of the array. I would find this
> > more useful, personally, and if I wanted the reader to check my numbers
>
> > 1. This sentence:
> >
> >     > The number of dimensions is inferred from the length of bounds it
> > would be impossible
> >
> >     sounds like it should have something between "bounds" and "it":
>
> Yes, I missed the semicolon.
>
> > 2. This part of the grammar:
> >
> >         bound := integer | "(" integer* ")
> >
> >     should be
> >
> >         bound := integer | "(" integer integer ")
>
> Another brain fart.
>
> > 3. The "integer" production should be modified to include prefixed
> > integers, like #xFF.
>
> I don't think this is an essential feature.  When would you naturally
> specify dimensions in strange bases?
>
> > 4. I would add an examples of 3D and 4D arrays, because those are going
> > to be less intuitive.
>
> Fair enough.