On Thu, Aug 24, 2017 at 2:14 PM, Philip McGrath <[email protected]> wrote:
> (->* (hash?) > () > #:rest (and/c list? > (λ (lst) > (let ([len (length lst)]) > (and (even? len) > (not (= 0 len)))))) > hash?) > > -Philip > Thanks, Philip! > > On Thu, Aug 24, 2017 at 1:08 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.
