inessential by Brent Simmons

Rob on Map (and Filter)

Rob Napier:

The mapping could be performed in parallel or in reverse order. It could be performed once and cached, or recomputed every time it’s accessed. In principle, we don’t care. As long as the mapping only depends on its inputs, and as long as there are no side effects, we will always get the same result. This is the heart of good functional programming.

(Via Michael Tsai.)