Thank you for your answer, but what about my specific example with pointer swapping? I‘d need a way to control memory handling in a procedural way in between pure state transitions. It probably goes further than that still - FP in general hides from me what happens with intermediate results on the hardware - I‘d need a way to have it use preallocated memory pools, because these operations are repeated in a very regular pattern (once per timestep or solver iteration) and thus always occupy the same memory. Versioning of previous states can (due to hardware limitations) only be done by file output. I‘ve never seen a pure FP language covering this because it seems to fundamentally go against purity principles, but as long as this is the case I reckon it‘s simply unusable for any but the smallest scale numerical applications.