On Sun, Nov 13, 2011 at 11:29 PM, Ryan Culpepper <r...@cs.utah.edu> wrote: > On 11/13/2011 09:21 PM, Sam Tobin-Hochstadt wrote: >> >> Many built-in structure type properties (such as `prop:procedure' and >> `prop:set!-transformer') support providing an integer index into the >> structure to reference a particular field that should supply the >> value. This is a very useful pattern, but unfortunately, it's not one >> that any Racket programs can use. In particular, the procedure >> calling mechanism and the expander get around the inspector system to >> implement this behavior. >> >> It would be nice if additional structure type properties could do this >> as well. Here's a suggestion of how it could work. >> `make-struct-type-property' adds an optional argument which specifies >> that an integer value is an index into the structure. In that case, >> the generated property accessor procedure performs the field lookup >> itself, avoiding the inspector system. Note that this doesn't reduce >> the power of the inspector system, since the structure type property >> value could be the struct accessor procedure paired with the index, >> and then you could write your own struct property accessor procedure >> that did the dispatch. This is less convenient for both users and >> definers, and thus it would be nice to build it in. > > I think you can do this yourself already using the guard argument of > make-struct-type-property. The guard function gets a list that "contains the > values that struct-type-info would return for the new structure type if it > skipped the immediate current-inspector control check".
Ah, that's very nice. Thanks! -- sam th sa...@ccs.neu.edu _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
