Re: [racket-users] How to check if a symbol is defined before calling it?

[Robby Findler]

Glad you found something that works!

For the record, being in a pkg and being an app are not mutually exclusive.
DrRacket, for example, enjoys both statuses.

Robby

On Sun, Feb 18, 2018 at 5:41 PM Alex Harsanyi 
wrote:

>
> Hi Robby,
>
> On Sunday, February 18, 2018 at 10:33:09 AM UTC+8, Robby Findler wrote:
>>
>> FWIW, the approach that is less friendly to your clients but perhaps
>> easier for you (and maybe good enough for them) is to declare a
>> dependency on a specific version in the info.rkt file of your pkg. The
>> pkg system will ensure that the latest version is used.
>>
>
> I have an application, not a package, so there is no "info.rkt" file in
> which to declare dependencies.  I do not use any external packages or
> features specific to a Racket version, so I did not need any version
> management of the libraries I use.  This is the first case where I need
> something that is not present in all racket versions -- in fact,currently,
> it is only present in an unreleased version.
>
> The suggested `dynamic-require` approach seems simple enough and it is
> probably more user (developer) friendly.  It also has the benefit that I
> understand how it works :-)
>
> Best Regards,
> Alex.
>
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Re: [racket-users] How to check if a symbol is defined before calling it?

[Alex Harsanyi]

Hi Robby,

On Sunday, February 18, 2018 at 10:33:09 AM UTC+8, Robby Findler wrote:
>
> FWIW, the approach that is less friendly to your clients but perhaps 
> easier for you (and maybe good enough for them) is to declare a 
> dependency on a specific version in the info.rkt file of your pkg. The 
> pkg system will ensure that the latest version is used. 
>

I have an application, not a package, so there is no "info.rkt" file in 
which to declare dependencies.  I do not use any external packages or 
features specific to a Racket version, so I did not need any version 
management of the libraries I use.  This is the first case where I need 
something that is not present in all racket versions -- in fact,currently, 
it is only present in an unreleased version. 

The suggested `dynamic-require` approach seems simple enough and it is 
probably more user (developer) friendly.  It also has the benefit that I 
understand how it works :-)

Best Regards,
Alex.

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Re: [racket-users] big-bang + right click?

[Stephen Foster]

Cool!  I was able to get it working with Lux.  Thanks!

On Saturday, February 17, 2018 at 9:34:19 AM UTC-8, Jay McCarthy wrote:
>
> FWIW Stephen, I have another package called `lux` that tries to be a 
> "professional" big-bang and it supports stuff like this. 
>
> The documentation is here: http://docs.racket-lang.org/lux/index.html 
>
> But I suggest checking out the two examples first. 
>
> val-demo --- 
> https://github.com/jeapostrophe/lux/blob/master/examples/val-demo.rkt 
> --- Shows how you can use 2htdp/image or pict to make your scenes and 
> it shows how the generic event-handler receives key events from 
> racket/gui. 
>
> spin --- https://github.com/jeapostrophe/lux/blob/master/examples/spin.rkt 
> --- is a little more complicated and shows how you get mouse event 
> structures as well as demonstrating that lux can be used recursively. 
> [For comparison, if you call big-bang inside a big-bang handler, then 
> a new window opens up. In lux, the same window is taken over and the 
> result from the inner call is returned to the call site. This can be 
> used to make things like pause screens, menus, and so on fairly 
> nicely.] 
>
> Jay 
>
> -- 
> -=[ Jay McCarthy   http://jeapostrophe.github.io]=- 
> -=[ Associate ProfessorPLT @ CS @ UMass Lowell ]=- 
> -=[ Moses 1:33: And worlds without number have I created; ]=- 
>

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[racket-users] Re: How to check if a symbol is defined before calling it?

[Jack Firth]

>
> The recent plot library introduces a new function, `point-pict` which is 
> not yet available as part of a Racket distribution, and the plot package 
> has to be installed separately from GitHub for this function.
>
> In my code I would like to be able to check if this function is available 
> before calling it, so my code compiles correctly even if the function is 
> not available.
>

In addition to the `dynamic-require` solution, you can do this statically 
with macros and `identifier-binding`:

(define-simple-macro (begin-when-bound id:id body ...+)
  #:with (body* ...) (if (identifier-binding #'id) #'(body ...) #'())
  (begin body* ...))

Warning: I have only written the above code, not run it. See also the 
version-case  package 
for a similar, more fleshed out concept.

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