Is the q solution equivalent? In doing a plus scan, isn't the last element always going to be the largest? To find the largest subarray sum, I would think you'd want to split into a matrix along the `null`s first and then plus reduction and then a max of those results.

Say what you will about clarity, but my mind sort of glossed over the intention in the python and rust code, focusing instead on the syntax, while the q code made me consider what was actually happening.