Skip holes when iterating over GAP lists?

[fingolfin]

Currently we have this:

julia> l = GAP.evalstr("[1,,3]")
GAP: [ 1,, 3 ]

julia> collect(l)
3-element Vector{Any}:
 1
  nothing
 3

Perhaps we should do what GAP does in this situation and just skip holes? I.e., do this:

julia> l = GAP.evalstr("[1,,3]")
GAP: [ 1,, 3 ]

julia> collect(l)
3-element Vector{Any}:
 1
 3

Note that this is purely about iteration. When converting to a vector, I'd expect things to stay as they are:

julia> Vector{Any}(l)
3-element Vector{Any}:
 1
  nothing
 3

Motivated by discussion at PR #967.

[ThomasBreuer]

I am not sure.

Julia does not know the concept of holes.
If we say that Julia shall interpret a GAP list with holes as an array of the same length as in GAP such that unbound entries correspond to nothing (this is what getindex does) then a different behaviour for iteration might look inconsistent.

On the other hand, we could define that Julia iteration over a GAP list is the same as GAP iteration.

In both cases, we mainly have to document the situation (also in the Oscar manual section on "Notes for users of other computer algebra systems").