the ()+()@<:> looks like ()+()@> ::operators reporter like in old versions, I don't know why the op would be using an old version of snap though.
I think the script is something they found from a long time ago by ego-lay_atman-bay somewhere on the forum. This would also explain why the image is not importable into Snap! (in version 7, the sum block is variadic but script pics weren't smart).
Yeah, I vaguely remember writing that script.