Re: [racket-users] Module dependencies

[Laurent]

You could also have a third file, test-a-and-b.rkt, that requires both
a.rkt and b.rkt and includes the test that depend on both files.


On Mon, May 28, 2018 at 10:08 AM Claes Wallin (韋嘉誠) 
wrote:

> (require) binds at compile time and creates a cycle, but by using
> (dynamic-require) you can get past compilation and only load the file at
> runtime, where the seemingly circular reference really isn't.
>
> --
>/c
>
> On Sun, May 27, 2018, 23:48 Matthias Felleisen 
> wrote:
>
>>
>> Modules cannot refer to each other in a cyclic fashion, including
>> submodules. — Matthias
>>
>>
>>
>> On May 27, 2018, at 8:33 AM, Brandon Irizarry 
>> wrote:
>>
>> Say I have two files, "file-a.rkt" and "file-b.rkt" that each contain a
>> submodule test, like so:
>>
>>
>> Contents of "file-a.rkt":
>>
>> #lang racket/base
>> (define (my-function) 'apple)
>> (module+ test
>> (require "file-b.rkt")
>> (other-function))
>>
>> Contents of "file-b.rkt":
>>
>> #lang racket/base
>> (define (other-function) 'orange)
>> (module+ test
>> (require "file-a.rkt")
>> (my-function))
>>
>> The require statements form a circular reference, even though running
>> file-b, along with its tests, shouldn't trigger file-a's tests.
>>
>> I've looked into compiling file-a and file-b, but that didn't work.
>>
>> - Brandon
>>
>>
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Re: [racket-users] Questions on functional-setter generator macro

[Greg Hendershott]

On Mon, May 28, 2018 at 9:58 AM, David Storrs  wrote:
> O *course* there is.  Lord know, why should I have an original idea
> now?  :P

The Racket package ecosystem is growing to where we need some
volunteers to form a mathic order of Lorites (like in Neal
Stephenson's novel, Anathem).

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Re: [racket-users] Questions on functional-setter generator macro

[David Storrs]

On Sat, May 26, 2018 at 3:11 PM, Alexis King  wrote:

> This isn’t a direct answer to your question, but as Matthias notes, my
> struct-update package already implements a macro that generates
> functional setters from structure definitions. Here’s a link to the
> documentation:
>

O *course* there is.  Lord know, why should I have an original idea
now?  :P



> http://docs.racket-lang.org/struct-update/index.html
>
> Of course, that isn’t especially helpful if your goal is to get better
> at authoring macros, not just generate functional setters. For that, you
> might find the (short) source code of struct-update helpful, located
> here:
>
> https://github.com/lexi-lambda/struct-update/blob/
> 8ce456cde8764ae27c348123ec9e01e76826d536/struct-update-lib/
> struct-update/main.rkt


Yes, thank you, this helps.  I hadn't thought about superclass fields.


> Admittedly, your make-functional-setter function does a bit more than
> define-struct-updaters, since it allows for a wrapper function. So I’ll
> also give some brief answers to a few of your unrelated questions.
>

I think we take a different approach -- struct-updaters always specifies a
contract of (-> struct-id? any/c struct-id) whereas make-functional-setters
offers the option to not have a contract or to specify whatever contract
you want.  I'm a firm believer in the idea that you should be allowed to
shoot yourself in the foot if you want the ability to do so.


> > On May 26, 2018, at 10:46, David Storrs 
> > wrote:
> >
> > A) Is there a way to test if a syntax class has a particular attribute
> > before trying to use it?
>
> Yes, use the attribute form. If x is an optional attribute, (attribute
> x) will be #f if the attribute was not bound and the value of the
> attribute if it was bound. If you want, you can change the default value
> to something else other than #f by providing the #:defaults option to
> ~optional.
>

Handy, thanks.


> > B) Alternatively, is there a way to create a null syntax object that
> > expands to nothing?  Not (void), not "", literally nothing.   Then I
> > could have each pattern bind all the attributes via #:with and just
> > have some of them be blank.
>
> Not in an arbitrary context. In a definition context, (begin)
> effectively expands into nothing, since begins are spliced into the
> enclosing context, but in an expression context, you can’t have
> something that expands into nothing.
>
> That said, it sounds like what you might actually want is the template
> and ?? forms from syntax/parse/experimental/template. This allows you
> to write something like this:
>
> (template (foo (?? x)))
>
> The above will be like #'(foo x) if (attribute x) is non-#f, but if it
> is #f, it will be like #'(foo). In Racket 6.12 and earlier, you must use
> the template form for ?? to work, but in Racket 7 and later, ?? will
> also work with the ordinary syntax (aka #') form, so if the word
> “experimental” spooks you, don’t worry about it too much.
>
> Alexis
>
>
This is really helpful, thank you.

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[racket-users] Unmap failed

[pavelrodzevich]

Hello, my name is Pavel and I'm new to Racket :)

I'm playing with macros right now and get a strange error: "unmap failed".

What I'm trying to achieve in this program: expand (step x) into (+ (expt 2 
0) (expt 2 1) ...)

For small numbers everything is OK, but I get an error for (step 100)

What does this error mean and how can I fix it?

Code is in attachements. 


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macro-step.rkt
Description: Binary data

Re: [racket-users] Module dependencies

[韋嘉誠]

(require) binds at compile time and creates a cycle, but by using
(dynamic-require) you can get past compilation and only load the file at
runtime, where the seemingly circular reference really isn't.

-- 
   /c

On Sun, May 27, 2018, 23:48 Matthias Felleisen 
wrote:

>
> Modules cannot refer to each other in a cyclic fashion, including
> submodules. — Matthias
>
>
>
> On May 27, 2018, at 8:33 AM, Brandon Irizarry 
> wrote:
>
> Say I have two files, "file-a.rkt" and "file-b.rkt" that each contain a
> submodule test, like so:
>
>
> Contents of "file-a.rkt":
>
> #lang racket/base
> (define (my-function) 'apple)
> (module+ test
> (require "file-b.rkt")
> (other-function))
>
> Contents of "file-b.rkt":
>
> #lang racket/base
> (define (other-function) 'orange)
> (module+ test
> (require "file-a.rkt")
> (my-function))
>
> The require statements form a circular reference, even though running
> file-b, along with its tests, shouldn't trigger file-a's tests.
>
> I've looked into compiling file-a and file-b, but that didn't work.
>
> - Brandon
>
>
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>
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