2.38.2 Rationale

The four procedures above have complex dependencies on one another, and it is inconvenient to have to pass them all to other procedures that might or might not make use of all of them. For example, a set implementation naturally requires only an equality predicate, but if it is implemented using a hash table, an appropriate hash function is also required if the implementation does not provide one; alternatively, if it is implemented using a tree, a comparison procedure is required. By passing a comparator rather than a bare equality predicate, the set implementation can make use of whatever procedures are available and useful to it.

This SRFI could not have been written without the work of Sebastian Egner and Jens Axel Soegaard on SRFI-67; much of the credit for this SRFI is due to them, but none of the blame. In addition, many of the design decisions of this SRFI are copied from SRFI-67’s design rationale.