I've added #:exists to provide/contract, as a way to hide information ala "type t" declarations on ML signatures.
See the contracts section in the Guide for a worked example and a discussion of a gotcha. The short version is that you can now write things like this: (provide/contract #:exists stack [new stack] [push (-> int stack stack)] [pop (-> (and/c stack non-empty?) int)] [non-empty? (-> stack boolean?)]) and have the contract system enforce data abstraction, even if your stack operations are simply these: (define new '()) (define push cons) (define pop car) (define non-empty? pair?) That is, clients of your module will not be able to treat your stacks as if they were lists, even though they really are lists. Robby _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
