On Fri, Oct 30, 2020 at 2:08 PM William J. Bowman <[email protected]> wrote:
> Let me aid this discussion by copying in the ~10 lintes of code in > question: > > > (define-syntax (dictof syn) > > (syntax-parse syn > > [(_ (k:id pred?) ...) > > (quasisyntax/loc syn > > (dictof/proc `((k . ,pred?) ...)))])) > > > > (define ((dictof/proc spec) h) > > (and (eq? (dict-keys h) (dict-keys spec)) > > (for/and ([(k pred?) (in-dict spec)]) > > (pred? (dict-ref h k))))) > > The macro is merely a syntactic transformation to 1 line of code that > implements > the functionality of the contract at run-time. > Is there some reason to avoid macros in this particular case? > > I don't think so. But I do think that you'd need more checking so things like (dictof (,(something scary) i-am-not-a-procedure)) give reasonable error messages. And eq? is probably not the right comparison (consider large integers for example). Robby > -- > William J. Bowman > > On Fri, Oct 30, 2020 at 03:04:04PM -0400, George Neuner wrote: > > > > On 10/30/2020 1:14 PM, William J. Bowman wrote: > > > Thanks! One follow-up: > > > > > > > 1. make these functions, not macros > > > The main implementation is a procedure, but I think I need a macro to > get the > > > syntactic interface I want. > > > > > > Is there some reason to avoid macros? > > > > You certainly can use macros in the implementation, but just remember > that > > macros evaluate at compile time and most contracts have to be checked at > > runtime: so a contract can't *exclusively* be a macro ... runtime code > has > > to be generated. > > > > Robby's comment about code size is relevant also: contracts are not > debug > > mode only like assertions in C ... Racket's contracts live on in release > > mode compiles, so you want to minimize the amount of runtime code > required > > to implement them. > > > > George > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/20201030190826.GA1988871%40williamjbowman.com > . > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAL3TdOOOcb0MnmWnj7bWP5SwnDzGr0zCTdcs_5hRWutGmHpF0Q%40mail.gmail.com.
