Thank you for the answer.
Could trampoline benefit for being enhanced by allowing an explicit
"escaping" for a return value of type function (that could also work
for other return types, but would not be necessary for the common
case).
Something like these :
- common usage : as usual
user=> (def myClosure #(prn "Hello"))
#'user/myClosure
user=> (trampoline myClosure)
"Hello"
- explicit escape via a "noboing" (or "stop" or "return" any name you
like) call (works for any return type) :
user=> (def myClosure (noboing #(prn "Hello")))
#'user/myClosure
user=> (trampoline myClosure)
#'user/myClosure
And it could be implemented as :
public final class org.clojure.lang.NoBoingWrapper {
public final Object returnInstance;
public NoBoingWrapper(Object returnInstance)
{ this.returnInstance = returnInstance; }
}
(defn noboing [returnInstance] (org.clojure.lang.NoBoingWrapper.
returnInstance))
and the modification of trampoline along these lines :
(defn trampoline [f]
(let [ret (f)]
(cond f
(fn? ret) (recur ret)
(instance? org.clojure.lang.NoBoingWrapper f) (.returnInstance
f)
else ret)))
HTH,
--
Laurent
On Nov 26, 10:38 pm, "Stephen C. Gilardi" <[EMAIL PROTECTED]> wrote:
> On Nov 26, 2008, at 4:32 PM, lpetit wrote:
>
> > I've maybe missed something, but will this work if one wants to make
> > the final return value of the tail call a closure ?
>
> Along the same lines of this being a manual way to do TCO, that issue
> will need to be handled manually as well. Here's what (doc trampoline)
> has to say about it:
>
> user=> (doc trampoline)
> -------------------------
> clojure.core/trampoline
> ([f] [f & args])
> trampoline can be used to convert algorithms requiring mutual
> recursion without stack consumption. Calls f with supplied args, if
> any. If f returns a fn, calls that fn with no arguments, and
> continues to repeat, until the return value is not a fn, then
> returns that non-fn value. Note that if you want to return a fn as a
> final value, you must wrap it in some data structure and unpack it
> after trampoline returns.
> nil
>
> --Steve
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