On 04/06/2014 02:33 AM, Henning Thielemann wrote: > Not exactly, because sortByKey memorizes the results of 'f' and (sortBy > . comparing) recomputes 'f' all the time. Racket language (PLT Scheme) has both variants, and I think both are needed – e.g. `length` of strings should probably be memorized, while something like `snd` or `negate` shouldn't.