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 <matth...@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.cava...@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. >> >> >> _________________________________________________ >> For list-related administrative tasks: >> http://lists.racket-lang.org/listinfo/users > > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/users _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
