Hi, Am 15.04.2009 um 14:04 schrieb Konrad Hinsen:
As an example, take algebraic data types as defined in clojure.contrib.types. A simple binary tree structure can be defined with (defadt ::tree empty-tree (leaf value) (node left-tree right-tree)) Values of this type are represented as maps in which the value associated with :clojure.contrib.types/tag is the constructor (`empty- tree, `leaf, or `node), with the :type in the metadata being ::tree. This double labelling makes sure that all tree values are recognized as being of the same type in dispatching, but also that equality tests take into account the constructor in addition to its arguments.
Maybe I'm missing something, but we can't you just derive ::leaf, ::empty-tree and ::node from ::tree? You can use ::tree in dispatch values, but the map still contains the constructor... Sincerely Meikel
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