It is for performance reasons. Specifically you can avoid creating the procedure over and over (if you're calling hash-ref over and over).
Robby On Sunday, July 18, 2010, Jos Koot <jos.k...@telefonica.net> wrote: > > > > > > (hash-ref > a-hash a-key a-value) > In the past > a-value was required to be a procedure. > Now it can > be anything. > > Nice. > Two caveats > though. > 1. If the > value of a-value happens to be a procedure to be stored, it may > unintentionally > be called. > 2. a-value > may be an expresssion that takes much computation. This computation is > repeated > every time the hash-ref line is evaluated. > > Simply > helped of course: I make it a habbit always to write or to have macros expand > to: > (hash-ref a-hash a-key (lambda () > a-value)) > > In short, I do not well understand the reason to relax > the contract of hash-ref and hash-ref!. > Jos > > > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
