Comparators

Note: There is now an IComparable protocol, which cljs.core/compare will make use of.

Problem statement

TODO

Terms

• comparison fn: boolean valued fn
• comparator: -/0/+ valued fn
• comp: either of the above

(These terms are not good, but I wanted one-word ways to talk about each idea below.)

Issues

• different underlying platform API
  • Java expects comparators (instances of Comparator)
  • goog expects comparison fns
• users care about composability, not abstractions
  • Clojure fns can be either comparators or comparison fns
  • implementation via wrapper in AFn's Comparable implementation
  • newly created fns just work
• protocols not helpful for implementation
  • if fns were some kind of IComparable, would just have to convert back to plain fns for goog to use them
  • don't see any obvious performance win
• protocols not helpful for consumers
  • making comp writers implement a protocol is just introducing a Javaism

Proposed Approach

• usage
  • no Comparable protocol
  • just use fns
• implementation
  • do AFn's wrapping work in a helper fn that wraps user fns inside sort

I am pretty confident about the usage. Less confident about implementation, but this can be improved later.