I agree with Mark. I often write ? versions of functions like member in my code when I write it the first time to show the "predicate intent".
Another important case is when you don't want internal values to "escape" to the client because you forget that member/and/etc return the thing, not #t. Jay On Thu, Nov 11, 2010 at 6:07 AM, Sam Tobin-Hochstadt <sa...@ccs.neu.edu> wrote: > On Thu, Nov 11, 2010 at 12:21 AM, Mark Engelberg > <mark.engelb...@gmail.com> wrote: >> >> I could loosen the types of these Booleans to be Any, but then I'm not >> really reflecting the "predicate intent" of these functions. > > This seems to be your primary issue. But I don't see why it's a > problem. In particular, you were happy with the semantics of `member' > in Racket before, but now that you want to write types or contracts, > you're unhappy. What were you writing down for the specification of > these functions before? For example: > > ;; Any -> ??? > (define (one-two-or-three? n) > (member n '(1 2 3))) > > What should we write for ??? here? I think that's the central > question, not anything for types or contracts. Maybe you wrote Any > here - then you should be fine with writing Any as a contract or a > type. Maybe you wrote TruthValue, or something like that - then you > can do exactly the same with types or contracts; see `truth/c' in the > documentation. > > Maybe you were writing 'Boolean' here before, and trusting that > nothing bad would happen, even though your specification was > incorrect. Now using contracts or types forces you to correct your > specification, and you'd prefer to change your semantics instead. > That's a reasonable argument to have, although I disagree. But it > isn't about types or contracts, it's about what the semantics of > `member' should be. > -- > sam th > sa...@ccs.neu.edu > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/users > -- Jay McCarthy <j...@cs.byu.edu> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93 _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
