Zip operator when an element is a Whatever

[alabamenhu]

The Problem

If using the zip operator on a list with an interior Whatever, the Whatever will be replaced with the previous element.

Expected Behavior

The expected behavior should preserve the interior Whatever object, as only when it's a final element does it repeat the previous element (per docs).

my @a = ['a', *, 'c']; 
my @b = [1,2,3]; 
say (@a Z @b); 
# ((a 1) (* 2) (c 3))

Actual Behavior

say (@a Z @b); 
# ((a 1) (a 2) (c 3))

Steps to Reproduce

See above code. Note that the cross operator X does not have the same error:

say (@a X @b); 
((a 1) (a 2) (a 3) (* 1) (* 2) (* 3) (c 1) (c 2) (c 3))

Environment

• Compiler version (rakudo -v or raku -v): v2024.02.110.g.18.abe.8.c.32

[lizmat]

It appears to be meant this way: the zip iterators appear to apply the Rakudo::Iterator.Whatever to the given iterables, and the internal documentation states:

    # Returns an iterator from a given iterator where the occurrence of
    # a Whatever value indicates that last value seen from the source
    # iterator should be repeated indefinitely until either another
    # non-Whatever value is seen from the source iterator, or the source
    # iterator is exhausted.

This behaviour does not appear to be documented. However, the spectests do have tests for it: removing the special Whatever handling, results in t/spec/S03-metaops/zip.t tests failing.

I propose we at least add a documentation issue. And maybe a problem-solving issue whether this behaviour is wanted or not. Or to have a way to disable it.