The fundamental problem is the syntax of identifiers. The rest is details. On Aug 18, 2010 11:25 AM, "Ray Racine" <<a href="mailto:ray.racine@gmail.com">ray.racine@gmail.com</a>> wrote: > This topic comes up so frequently (schemes structure accessors/mutators) , > and has been independently solved in and around the same conceptual solution > (a chaining dot syntax) that I've often wondered why Racket would not make > such a capability "core" to the language. It seems such an obvious > absolutely should (to some) that I'm interested in hearing the counter > position of why it should not. > > Thanks, > > Ray > > On Wed, Aug 18, 2010 at 10:52 AM, Matthias Felleisen > <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>>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 <<a href="mailto:wayo.cavazos@gmail.com">wayo.cavazos@gmail.com</a>> >> 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: >> > >> > <a href="http://gist.github.com/364754">http://gist.github.com/364754</a> >> > >> > 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. >> > >> > >> > _________________________________________________ >> > For list-related administrative tasks: >> > <a href="http://lists.racket-lang.org/listinfo/users">http://lists.racket-lang.org/listinfo/users</a> >> >> _________________________________________________ >> For list-related administrative tasks: >> <a href="http://lists.racket-lang.org/listinfo/users">http://lists.racket-lang.org/listinfo/users</a> >> > > > > -- > The object of life is not to be on the side of the majority, but to escape > finding oneself in the ranks of the insane. - Marcus Aurelius