[ Exec summary: dependent contracts aren't slow anymore, so use them more! ]
There are not many uses of dependent contracts in our git respository or in planet. I have a sense that people avoid dependent contracts because they are slow. While ->d is remarkably slow, I'm not sure how widespread this impression is or if it really is a reason but I've gone ahead and improved dependent contract's performance with a new contract combinator, ->i (this guy is motivated by Christos Dimoulas's research so is different from ->d in how it deals with contracts that "break themselves" but I'll leave that story for another time). Performance-wise, the main difference between ->d and ->i is that you have to be more explicit about the dependencies between arguments with ->i contracts. Specifically, if one argument depends on another one, then you have to list that. For example, in this contract: (->i ([x (y) (<=/c y)] [y integer?]) [res integer?]) The contract on x depends on the value of y, and the list of variables "(y)" in the clause for the x argument indicates that. Also, since y does not depend on the values of the function arguments, then it has no list at all. This is the corresponding ->d contract, where such lists are not part of the syntax: (->d ([x (<=/c x)] [y integer?]) [res integer?]) The ->i contract runs 12x faster than the ->d one (when checking the function (lambda (x y) (+ x y))). Even better, the ->i contract above runs within an epsilon of the time that the contract (-> integer? integer? integer?) runs, for the same example. So, please do try using dependent contracts more! Robby _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
