On Mar 7, 2010, at 10:57 PM, CuppoJava wrote:
> Is there an elegant solution to this problem? I'm working around it by
> saving the original println in another variable before creating
> myprintln, but this isn't very clean.
In case by another "variable", you were referring to another "var":
One relatively clean way to capture the old value is in a closure:
user=> (let [println println]
(defn myprintln [str]
(println str)
(println "tacked on")))
#'user/myprintln
This doesn't work in the current head of Clojure because by default, calls to
functions bound to vars in namespaces whose names begin with "clojure" (e.g.,
clojure.core) are inlined by the compiler. Binding the var has no effect on how
the compiled code runs. My understanding is that this is an experimental
optimization that Rich is trying out.
Wrapping println in a bindable wrapper (in the user namespace) proves the
concept:
user=> (defn _println [x] (println x))
#'user/_println
user=> (let [_println _println]
(defn myprintln [str]
(_println str)
(_println "tacked on")))
#'user/myprintln
user=> (binding [_println myprintln] (_println "Some code"))
Some code
tacked on
nil
user=>
--Steve
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