array2d indexing - allow str input to automatically parse range

[kalekje]

Before I start a fork/pull request, I just wanted to see interest in this idea,

We can index a 2d array with ints, or use the parse_range on a string. Can we allow this to be done automatically if i1 is a string?

function array2d.default_range (t,i1,j1,i2,j2)
 -- my patch
    if (type(i1) == 'string') and not (j1 or i2 or j2) then
        i1, j1, i2, j2 = array2d.parse_range(i1)
    end
--
    local nr, nc = array2d.size(t)
    i1 = norm_value(i1 or 1, nr)
    j1 = norm_value(j1 or 1, nc)
    i2 = norm_value(i2 or nr, nr)
    j2 = norm_value(j2 or nc, nc)
    return i1,j1,i2,j2
end

Additionally, I would like to add another flavor of string indexing: numpy-like indexing. I have the method worked out and would like to implement it. Currently, I cannot patch the array2d.default_range (after loading penlight that is, without modifying the source code) because the usage of default_range uses the local function default_range.. which begs the question, why does array2d.default_range exist then? I propose that we remove the local default_range and instead use the module function array2d.default_range for all uses.

[Tieske]

We can index a 2d array with ints, or use the parse_range on a string. Can we allow this to be done automatically if i1 is a string?

That does make sense to me. PR welcome!

which begs the question, why does array2d.default_range exist then?

Locals are faster, hence internally we use a local, and we also export the function on the module for external uses.

[Tieske]

closing in favour of #404