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.
