How the HACSEL Library Came About Using Applicatives

The HACSEL library gives you this way to parallelize things by using applicatives. And it works very nicely if you're using something like NAPM because you get parallelism for free if you map M a function over a list. So that's how applicative do came about but many do statements don't completely turn into applicatives. The idea is that sometimes you have applicatives where you want to explore multiple branches and then give up if one of the branches fails. This turns out to be really useful in some of the cases that we needed to implement in Sigma.