[racket] syntax, differently

Nice idea. I second that. 


On Aug 18, 2010, at 11:14 AM, Jay McCarthy wrote:

> This is a price you are already paying in Typed Racket. I'd like to see more ways of putting types to work implemented. 
> 
> Jay
> 
> Sent from my iPhone
> 
> On Aug 18, 2010, at 8:52 AM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
> 
>> 
>> Eduardo is providing a macro that helps you abbreviate complex 
>> selector and mutator chains. The BENFIT you get is that instead
>> of writing 
>> 
>> (posn-x (bird-posn (sky-bird (world-sky some-world))))
>> 
>> you can write -- in Racket -- 
>> 
>> some-world.sky.bird.posn.x 
>> 
>> and make Racket programs look as short as C program selectors 
>> or Java dots or Javascript dots etc. 
>> 
>> The PRICE you pay is that you annotate variables and fields
>> with struct information. That is, you have to say somewhere that 
>> some-world is a variable that always stands for a world struct. 
>> And the sky field in world has to come with information that it 
>> always is a sky-struct. And so on. 
>> 
>> ;; --- 
>> 
>> To make this available in Racket, you'd have to port his macros
>> from R6RS Scheme to Racket. I suspect that this would be a minor
>> task. 
>> 
>> ;; --- 
>> 
>> To make this available in the teaching languages, you'd have to 
>> export these macros in a way that makes sense for students. Or
>> you keep it all private to yourself. 
>> 
>> ;; --- 
>> 
>> I assume that you understand the differences between the various 
>> operations.  In Java,
>> 
>> pos.draw
>> 
>> comes with static knowledge about pos (an object of a certain type)
>> and draw (a field of a certain type) that is exploited to make the
>> notation short and safe. It isn't complete safe because of NULL, 
>> which doesn't exist in Racket or the teaching languages, but let's 
>> ignore that. 
>> 
>> In a language like Ruby, 
>> 
>> pos.draw
>> 
>> just doesn't care, If pos has an draw field at run-time, good enough. 
>> Even if pos isn't a position but happens to have a draw field, just 
>> keep on computing. 
>> 
>> In Racket and the teaching languages, you are *forced* to write 
>> down what kind of struct you expect and what field you want: 
>> 
>> pos.check-it-is-a-posn-and-select-x-then
>> 
>> This gives you safety a la Java (at run-time) and tells the reader
>> at each site where you write down a selector expression what you 
>> expect. It's verbose but readable. 
>> 
>> 
>> 
>> 
>> On Aug 18, 2010, at 10:34 AM, Mathew Kurian wrote:
>> 
>>> 
>>> 
>>> On Wed, Aug 18, 2010 at 2:41 AM, Eduardo Cavazos <wayo.cavazos at gmail.com> wrote:
>>> 
>>> Mathew Kurian:
>>> 
>>> However, in the case of universe/world teachpacks, where the use of
>>> states is a vital component, a set of code can get very long,
>>> especially if the program is very complex and contains multiple
>>> structures (in some cases structures inside structures inside
>>> structures) within the states.
>>> 
>>> I agree with the critique of lengthy expressions involving nested records (structs).
>>> 
>>> Here's how I deal with it:
>>> 
>>>  http://gist.github.com/364754
>>> 
>>> The particular solution is for R6RS but PLT has the necessary mechanisms for it.
>>> 
>>> Ed
>>> 
>>> Hey Ed,
>>> 
>>> If you have spare time, can you please explain by what you meant in that github website. All I saw was a comparison between C and Scheme.
>>> 
>>> Thank you
>>> 
>>> Mathew K.
>>> 
>>> 
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