Sensible default distance function, based on ===

Given an Iterable of [key, value] entries, applies the distance function to each key, finding the one closest to the input key, also returning its associated value as well as the related distance; returns undefined only when there are no successful match - that is, all the keys have +inf distance.

The distance between two values; a non-negative real number between:

Measures the distance between two values.

Match between a reference key and the closest key in a [key, value] collection: