Keep in mind that case also isn't really cheap. There's an infinite number of symbols so there is no cheap jump table. -- Matthias
On Dec 22, 2014, at 10:10 PM, J Arcane wrote: > Thanks for the insight. I hadn't considered the performance implications > involved I suppose (the perpetual problem of the young Lisper ...) > > And evcase does indeed work more like I expected, for example: > > (for ([n (in-range 1 101)]) > (evcase 0 > ((+ (modulo n 5) > (modulo n 3)) (displayln "FizzBuzz")) > ((modulo n 5) (displayln "Buzz")) > ((modulo n 3) (displayln "Fizz")) > (else (displayln n)))) > > Works exactly as I'd expect. I'll have a look at the code and see if any > further insights might be found there for Heresy's (select case ...) > > Thanks! > > On Mon, Dec 22, 2014 at 5:20 PM, Matthias Felleisen <matth...@ccs.neu.edu> > wrote: > > Look for evcase. -- Matthias > > > On Dec 21, 2014, at 11:58 PM, J Arcane wrote: > > > Up with a horrible ear-ache this morning I decided to include a FizzBuzz > > example in Heresy, the Racket #lang I've been working on, and ran into an > > unexpected behavior in the (case ...) statement. > > > > In many languages with case, you can make the testing value a constant, and > > then make the matching clauses actual calculations which then match against > > that constant. So when doing FizzBuzz in C-like languages you can do > > something like "switch 0" and then "case x % 3" for the matching clauses. > > > > It turns out this doesn't work in Racket, because Racket quotes the values > > in the matching clauses so they do not evaluate. Specifically, it narrows > > down to doing this in (case/sequential-test ...): #`(equal? v 'k) > > > > I can implement an alternate version that works as I expect (and will > > probably include it in Heresy) just by removing that quote in my version, > > but I was curious as to the reasoning behind this behavior and if perhaps > > there's some explanation for it that I may've missed. > > > > Any insights appreciated, > > John Berry > > > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > >
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