Or something like this, with the rackjure package:
(require rackjure/threading 2htdp/image)
(~>> background-img
(place-image image-1 x y) ; the background-img will be inserted as the
last argument, because that's what ~>> does
(place-image image-2 x y) ; the background + image-1 will be inserted as
the last argument
(place-image image-3 x y) ; and so on
...)
Or if you don't want to use rackjure, then with let* it would be:
(let* ([img background-img]
[img (place-image image-1 x y img)]
[img (place-image image-2 x y img)]
[img (place-image image-3 x y img)]
...)
img)
On Aug 24, 2015, at 2:40 PM, Joel McCracken <[email protected]> wrote:
> This would be where I would reach for a let* to handle intermediate
> results, because code like this is very awkward.
>
> On Mon, Aug 24, 2015 at 2:32 PM, John Carmack <[email protected]> wrote:
>> The idea that you functionally compose images like this:
>>
>> (place-image image-1 x y
>> (place-image image-2 x y
>> (place-image image-3 x y)))
>>
>> Which draws image1 on top of image2 on top of image 3, which is backwards
>> from the "painters order" that would draw image 3, then image 2, then image
>> 1.
>>
>> This imperative, side-effect-ing code is a little less clear to a beginner
>> with the OOP and DC concepts, but It better represents what actually
>> happens, and it is much easier to modify the code without worrying about the
>> nesting.
>>
>> (send dc draw-bitmap imag3 x y)
>> (send dc draw-bitmap imag2 x y)
>> (send dc draw-bitmap imag1 x y)
>>
>> -----Original Message-----
>> From: [email protected] [mailto:[email protected]]
>> On Behalf Of David Grenier
>> Sent: Monday, August 24, 2015 1:14 PM
>> To: Racket Users
>> Cc: John Carmack
>> Subject: [racket-users] Re: My son's game in Racket
>>
>> On Monday, August 24, 2015 at 12:28:07 PM UTC-4, John Carmack wrote:
>>> We “released” my 10 year old son’s game that was done in Racket:
>>> www.1k3c.com
>>>
>>>
>>>
>>> I’m still taking a little heat from my wife for using an obscure
>>> language instead of something mainstream that is broadly used in industry,
>>> but I have nothing but good things to say about using Racket and DrRacket
>>> for a beginning programmer, and highly recommend it.
>>>
>>>
>>>
>>> I can’t recommend 2htdp/universe for this sort of thing, though. I
>>> had to drop to the native GUI bitmaps for performance reasons, hack around
>>> the lifecycle to support a separate editor window, and I still don’t know
>>> how to make the Quit menu item actually exit the app on the Mac version.
>>>
>>>
>>>
>>> I completely understand the reasoning for the way 2htdp/universe is
>>> built, and saying that a “real” project should use the grown-up APIs is
>>> fine, but the evolution from making a little animation to controlling it
>>> somehow to fleshing it out into a game is so natural that recommending a
>>> fairly big rewrite is unfortunate.
>>>
>>>
>>>
>>> I’m a big booster of functional programming, but I’m not sure that the
>>> functional drawing paradigm ever really sank in while my son was working
>>> with it, rather it felt like you just drew everything backwards with
>>> missing parenthesis at the end. I suspect that using the standard
>>> imperative GUI drawing code will make perfect sense to him.
>>>
>>>
>>>
>>> I’m not sure yet if we are going to migrate to the regular GUI code for
>>> upcoming work, or jump all the way to OpenGL so he can learn the joys of
>>> “Why is the screen all black?”
>>>
>>>
>>
>> Not clear what was meant both times you wrote "backwards" are you referring
>> to the lisp-style function call? Something that could be alleviated by say
>> F#'s pipe forward operator?
>>
>> let (|>) a f = f a
>>
>> or Clojure's -> macro?
>>
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>
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