Hi, Am 26.01.2009 um 18:15 schrieb gun43:
(defmacro deftarget [sym doc & forms]
(let [has-run-fn (gensym "hr-" ) reset-fn (gensym "rf-" )]
`(let [[~has-run-fn ~reset-fn once-fn#] (runonce (fn [] ~...@forms))]
(def
~(with-meta
sym
{:doc doc :has-run-fn has-run-fn :reset-fn reset-fn})
once-fn#))))
But with-meta does not:
user=> (def (with-meta 'bah3 {:doc "say bah 3 times"}) #(println "bah
bah bah"))
java.lang.Exception: Second argument to def must be a Symbol
(NO_SOURCE_FILE:12)
although with-meta returns a symbol:
user=> (class (with-meta 'bah3 {:doc "say bah 3 times"}))
clojure.lang.Symbol
def is a special form. Its second argument doesn't get evaluated. Hence def sees the (with-meta ..) itself, not its value, the symbol. Hence you get the Exception. In the macro this works, because the with-meta there is evaluated before the resulting (def ..) form is passed on to the compiler. So the def here really sees the symbol. Hope this helps. Sincerely Meikel
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