While trying to understand the doubly indented lines in the following
definition from "Programming Clojure" by Stuart Halloway:
(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#))))
I made the following confusing discovery:
#^ works as expected:
user=> (def #^{:doc "say bah 2 times"} bah2 #(println "bah bah"))
#'user/bah2
user=> (bah2)
bah bah
nil
user=> ^#'bah2
{:ns #<Namespace user>, :name bah2, :file "NO_SOURCE_FILE", :line 5,
:doc "say bah 2 times"}
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
which has the expected metadata:
user=> (meta (with-meta 'bah3 {:doc "say bah 3 times"}))
{:doc "say bah 3 times"}
Am I not understanding something or is there a bug here?
Thanks
gun43
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