What it is ---------- Trammel is a [Clojure](http://clojure.org) providing contracts programming (sometimes called "[Design by Contract](http://en.wikipedia.org/wiki/Design_by_Contract)" or DbC) capabilities. Features of Trammel currently include:
* Contracts on functions * Composable contracts * Post-definition function contract application * defrecord and deftype invariants * Reference type invariants (i.e. Agents, Atoms, Refs, and Vars) * Ability to turn-off checks in a production setting * Support for Clojure versions 1.3 and 1.4 Trammel is inspired by [Eiffel](http://www.eiffel.com/) and [Racket Scheme](http://docs.racket-lang.org/reference/contracts.html). Absorb ------ You can use Trammel in your [Leiningen](https://github.com/technomancy/leiningen) and [Cake](https://github.com/flatland/cake) projects with the following `:dependencies` directive in your `project.clj` file: [trammel "0.7.0] For Maven-driven projects, use the following slice of XML in your `pom.xml`'s `<dependencies>` section: <dependency> <groupId>org.clojure</groupId> <artifactId>trammel</artifactId> <version>0.7.0</version> </dependency> Enjoy! Places ------ * [Source code](https://github.com/fogus/trammel) * [Ticket system](https://github.com/fogus/trammel/issues) * [Examples and documentation](http://fogus.github.com/trammel/) -- in progress * [Dream Date](http://github.com/fogus/dream-date) - an example project using Trammel -- in progress Changes from version 0.6.0 -------------------------- * Better assertion error reporting * Ability to add constraint descriptions used in assertion reporting * Constrained defrecords no longer support default field values * Constrained defrecords no longer generate keyword args ctor function * Reference type invariants Reference type invariants work in the following ways. ### Atoms Atoms are created directly with their invariants: (def a (constrained-atom 0 "only numbers allowed" [number?])) @a ;=> 0 And checked on change: (swap! a inc) ;=> 1 Invariant violations are reported right away: (swap! a str) ; Pre-condition failure: only numbers allowed (compare-and-set! a 0 "a") ; Pre-condition failure: only numbers allowed ### Refs Refs are created directly with their invariants: (def r (constrained-ref 0 "only numbers allowed" [number?])) And also checked on change, within a transaction: (dosync (alter r inc)) ;=> 1 (dosync (alter r str)) ; Pre-condition failure: only numbers allowed ### Vars Vars are created directly with their invariants: (defconstrainedvar ^:dynamic foo 0 "only numbers allowed in Var foo" [number?]) Var invariants are checked on rebinding, such as with `binding`: (binding [foo :a] [foo]) ; Pre-condition failure: only numbers allowed ### Agents Agents are created directly with their invariants: (def ag (constrained-agent 0 "only numbers allowed" [number?])) And are checked on `send` and `send-off` (send ag str) (agent-error ag) However, the invariant violations are reported consistently with the agent setup. In this case, the errors are accessible via the `agent-error` function. Plans ----- The following capabilities are under design, development, or consideration for future versions of Trammel: - Contracts for higher-order functions - Better error messages - `defconstraint` -- with ability to relax requires and tighten ensures - Modify macros to also allow regular Clojure constraint maps - Allow other stand-alones: true/false, numbers, characters, regexes - Marrying test.generative with Trammel - More documentation and examples More planning is needed around capabilities not listed nor thought of. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
