Re: [racket-users] Class constracts and equality

Hi Konrad, On 2015-09-01 20:42:42 +0200, Konrad Hinsen wrote: > Thanks for the reference, but my interpretation of this is different. I > don't care about eq?, nor about testing how objects were created. I want > comparison by equal? by recursive application to the fields - just as for >

Re: [racket-users] Class constracts and equality

On 01/09/15 18:45, Daniel Feltey wrote: I think this is expected, if you want to check for equality on instances of contracted classes you should use the `object=?` function which can "see through" the contract wrappers.

Re: [racket-users] custom-print called twice?

The first call is to detect sharing, and the second time is to actually print. For example, if you change `(constr 'y)` to (define b (box #f)) (set-box! b (constr b)) b then you'll see that the output starts with "#0=", because the first pass detected that a "#0#" will be needed. At Wed,

Re: [racket-users] TR + Vector containing opaque struct

The best solution is usually to avoid using Any when interoperating with untyped code. Presumably you can describe a more specific type for this case, such as an opaque type for the sql-null value. Sam On Tue, Sep 1, 2015, 3:03 PM 'John Clements' via Racket Users < racket-users@googlegroups.com>

[racket-users] TR + Vector containing opaque struct

I’m trying to use the database library db with TR, and I’ve run into a problem whose only workaround seems really nasty. Specifically, it concerns vectors (or lists, presumably) that contain opaque values. So, for instance, here’s foo1.rkt: #lang racket (provide return-a-list) (struct

[racket-users] custom-print called twice?

Question: why is in the following example the custom-printer called twice? #lang racket (define n 0) (letrec-values (((printer) (λ (obj port mode) (set! n (add1 n)) (fprintf port "#" (name obj ((id constr pred acc mut) (make-struct-type 'x #f 1 0 #f (list

[racket-users] Help needed with: "cannot instantiate `racket/gui/base' a second time in the same process context"

Hi, I uploaded my very first package and scribble docs to the Racket package server. It seems that there is something wrong in my scribble files since the docs don't show up and I get this error: "cannot instantiate `racket/gui/base' a second time in the same process context"? Here is the

Re: [racket-users] Help needed with: "cannot instantiate `racket/gui/base' a second time in the same process context"

The problem is that the documentation-build process cannot support a use (direct or indirect) of `racket/gui/base` at documentation-build time. The @(require teachpacks/racket-turtle) in your ".scrbl" files is the main problem, since that indirectly loads `racket/gui/base`. It looks like you

Re: [racket-users] How to use the web-server package without continuations?

On Tue, Sep 1, 2015 at 10:03 AM, Ben wrote: > Hi, > > I'm trying to build a web application using Racket. But I don't understand > continuations yet. I think the package is capable of writing simple > applications without continuations. So > > 1. Which part of the web-server

[racket-users] How to check a place-channel for a message without blocking?

Is there a way to check whether there is a message available to be picked up on a place-channel without blocking? (If there isn't, the only way forwards for me in Racket is via a server. possibly a tcp server, though I don't really want the handshake. Possibly a Unix Socket Server. Possibly

[racket-users] How to use the web-server package without continuations?

Hi, I'm trying to build a web application using Racket. But I don't understand continuations yet. I think the package is capable of writing simple applications without continuations. So 1. Which part of the web-server package should I stay away from if I don't want to use continuations? 2.

[racket-users] Class constracts and equality

Hi everyone, I am trying to add a contract to a class but find that the mere presence of the contract breaks my code. Here is a minimal example that illustrates the problem: -- #lang racket (define foo% (class object% (inspect #f)