You may want to have a look at unstable/generics: http://docs.racket-lang.org/unstable/Generics.html?q=unstable/generics
It's currently unstable, but I'm working on moving it to a more permanent place in the near future, hopefully by the next release. Vincent At Sun, 4 Mar 2012 14:15:55 -0800, Helmut Rohrbacher wrote: > > [1 <multipart/alternative (7bit)>] > [1.1 <text/plain; ISO-8859-1 (7bit)>] > So I have code that looks similar to this toy example in a Common Lisp > project: > > > (defgeneric to-list (data) > (:documentation "Convert given data type to a proper list")) > > (defmethod to-list ((data list)) > list) > > (defmethod to-list ((data vector)) > (coerce data 'list)) > > (defmethod to-list ((data binary-tree)) > (traverse #'(lambda (x) x) data 'in-order)) > > ;;; ... So on for other collection datatypes ... > > > This way I can write a function to work on multiple collection types > without having to define multiple methods to specialize on each. In > addition it allows me to define TO-LIST method for any future types I would > to use those functions on. From what I understand this would be done > similarly in Haskell with a type-class: > > class Listable a where > > toList :: a -> [b] > > But I am not a Haskell expert, and my code doesn't literally have TO-LIST. > > I see that Racket has generic functions, but they see to work a bit > differently that CLOS-style generics. Further, like Haskell's type-classes > I would like to be able to provide a contract for functions that take a > Listable type: > > (provide > > (contract-out > > <...> > > [foo (-> listable? bar?)] > > <...>)) > > > I can do this in CL using a :BEFORE method > > (defmethod foo :before ((collection t) <...>) > > (unless (find-method #'to-list () (list (class-of collection)) nil) ; > ensure collection object has TO-LIST method > > ; otherwise raise error condition) > > <...>) > > What would be the appropriate Racket construct or idiom to get sort of > "type-class" or "interface" that can be enforced through contracts? > > Thanks, > Helmut > [1.2 <text/html; ISO-8859-1 (quoted-printable)>] > > [2 <text/plain; us-ascii (7bit)>] > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
