Easy - vector-ref with a negative index is not defined in r[5|7]rs. On Sun, 20 Dec 2020 at 06:59, Aleix Conchillo Flaqué <aconchi...@gmail.com> wrote:
> Hi, > > This month I'm trying to go through Advent Of Code one more year > (previous years I didn't get too far) and I've been finding myself > writing the same patterns multiple times that could be avoided by just > having a helper function. > > One of them is getting the last element of a vector. It is a quite > common operation when solving these types of problems. For example > Python as you might know uses negative indices. > > I have looked around and haven't seen it (unless I completely missed > it which would be shameful) but wouldn't it be good to have this > built-in by default? > > Instead of having to write: > > (vector-ref v (- (vector-length v) 1)) > > you would write: > > (vector-last v) or even better (vector-ref v -1). > > Interestingly Racket doesn't offer those functions either as far as I can > tell. > > Basic use case? Get the maximum element of a sorted vector which would > be done in constant time. > > I'm trying to solve the problems idiomatically, to the best of my > limited knowledge, with Scheme. It is possible that the times I'm > using vectors I should think about it differently and not use them, > but I'm not 100% sure. > > What am I missing? > > Thank you in advance, > > Aleix > >
