That example is sort of a thing in compilers. It's possible to recognise the two traversals, synthesise a new function which does both jobs, traverse once, disa

That example is sort of a thing in compilers. It's possible to recognise the two traversals, synthesise a new function which does both jobs, traverse once, disassemble the result. Gets called things like "map fusion" or "kernel fusion". I haven't seen it done robustly.