On 2012-09-24 22:00:29 -0700, Gregory Woodhouse wrote: > In writing contracts for classes I always use the ->m constructor for > methods, so this example of section 5.1 of the Reference surprises me > > (define file-interface<%> > (interface () open close read-byte write-byte)) > (define directory-interface<%> > (interface (file-interface<%>) > [file-list (-> (listof (is-a?/c file-interface<%>)))] > parent-directory)) > > It looks like -> contract constructor means the same thing except, of > course, the context is an interface definition and a class contract, so > it's clear from context that this a method and not a function.
The `->` there is a typo and it should actually be `->m`. I'll fix the docs for the next release. Note that you *can* use `->` for method contracts though, in which case you need to specify an extra argument corresponding to the `this` argument implicitly passed to methods. > Second question: Is the inclusion of contracts in interface definitions a > new feature? I've always written interfaces using only method names and > have missed the ability to specify the shape of the method (something more > analogous to what a Java interface does). It's entirely possible that this > has been in the Reference a long time and I just missed it. In fact, I'm > continually amazed at how much is there that I've missed. Yes, it's a new feature that was included in Racket 5.3. Interface contracts are complementary to `class/c` contracts and work slightly differently. Most importantly, any class that implements an interface (either directly or indirectly) with a contracted method will also have a contract on that method. Cheers, Asumu ____________________ Racket Users list: http://lists.racket-lang.org/users
