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. -- sam th sa...@ccs.neu.edu _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
