On Mon, Sep 10, 2018 at 2:18 PM, Alexis King <lexi.lam...@gmail.com> wrote:
> I think the answer here really is “don’t use `contract` directly”. The > actual implementation of the contract system does some fancy rebinding > of my-func when you use define/contract, turning this: > > (define/contract x ctc rhs) > > into this: > > (define x-awaiting-neg > (let ([tmp rhs]) > (lambda (neg) (contract ctc tmp 'x neg)))) > > So specifying the negative party is deferred. It then defines an > additional syntax binding that supplies the negative party based on the > use site of x, which works like something along these lines: > > (define-syntax x > (make-variable-like-transformer > #'(x-awaiting-neg (quote-module-name)))) > > where `quote-module-name` comes from syntax/location. > > This isn’t 100% accurate to what the contract system actually does, but > the gist is that the negative party represents the client, so somehow > you need to arrange for a different value to be supplied depending on > what the client party actually is. > > Getting this right is tricky, so stick to contract-out, define/contract, > with-contract, and define-struct/contract, which are the sanctioned > contract attachment forms. For macros, there’s also `expr/c` syntax > class from syntax/parse and the equivalent `wrap-expr/c` function from > syntax/contract. Those will work out the tricky machinery for you behind > the scenes, and they usually cover all the potential use cases. If you > have some other use case that isn’t served by those contract attachment > forms, by all means share it, but it’s hard to advise how to use > `contract` properly in a vacuum. > Got it. Okay, that fits my needs. Thanks, Alexis. > > On Sep 10, 2018, at 12:40, David Storrs <david.sto...@gmail.com> wrote: > > > > (define (my-func thunk-arg) > > (contract integer? (thunk-arg) 'my-func <CALLER>)) > > > > What should I replace <CALLER> with? > > > > > > NB: I know that in the example I could do > > (define/contract (my-func thunk-arg) (-> (-> integer?) integer?) > (thunk-arg)) > > but I'm looking for an answer to the generic case. > > -- 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 racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
