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vector-last / vector-ref with negative indices?

From: Aleix Conchillo Flaqué
Subject: vector-last / vector-ref with negative indices?
Date: Sat, 19 Dec 2020 22:58:40 -0800


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,


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