`recursive-contract` is really just a `delay` that that contract system knows how to implicitly `force`.
Sam On Thu, Aug 24, 2017 at 2:54 PM, David Storrs <[email protected]> wrote: > > > On Thu, Aug 24, 2017 at 2:22 PM, Sam Tobin-Hochstadt <[email protected]> > wrote: >> >> I think this is roughly what you want: >> >> >> #lang racket >> >> (define/contract (safe-hash-set h . args) >> (->* (hash?) () #:rest (letrec ([c (recursive-contract (or/c null? >> (cons/c any/c (cons/c any/c c))))]) c) hash?) >> ...) >> >> (safe-hash-set (hash) 1) >> >> Sam > > > Thanks, Sam. I'll need to do some reading on recursive-contract to make > sense of this, but I appreciate the pointer. > > Dave > >> >> >> On Thu, Aug 24, 2017 at 2:08 PM, David Storrs <[email protected]> >> wrote: >> > I'd like to be able to write a function that makes it easy to set one or >> > more keys in a hash, without worrying about whether the hash is mutable >> > or >> > not. It could be called in any of the following ways: >> > >> > (define imm-h (hash 'a 1)) >> > (define mut-h (make-hash '((a . 1)))) >> > >> > (safe-hash-set imm-hash 'x 2) ; returns (hash 'a 1 'x 2) >> > (safe-hash-set imm-hash 'x 2 'y 7) ; returns (hash 'a 1 'x 2 'y 7) >> > >> > (safe-hash-set mut-hash 'x 2) ; returns (begin (hash-set! mut-h >> > 'x 2) >> > mut-h) >> > (safe-hash-set mut-hash 'x 2 'y 7) ; returns (begin (hash-set! mut-h 'x >> > 2) >> > (hash-set! mut-h 'y 7) mut-h) >> > >> > This definition isn't quite what I need: >> > (define (safe-hash-set h . args) >> > (->* (hash?) () #:rest (non-empty-listof any/c) hash?) >> > ...) >> > >> > I want to be able to say "the rest argument is a list that has an even >> > number of elements and more than zero elements", but I'm not sure how to >> > capture that. Thoughts? >> > >> > Dave >> > >> > -- >> > 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]. >> > For more options, visit https://groups.google.com/d/optout. > > > -- > 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]. > For more options, visit https://groups.google.com/d/optout. -- 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]. For more options, visit https://groups.google.com/d/optout.
