On Sep 30, 9:07 pm, Chouser <[EMAIL PROTECTED]> wrote:
> On Tue, Sep 30, 2008 at 7:24 PM, dherring <[EMAIL PROTECTED]> wrote:
>
> > Related question: Is there any way to "return" side-channel data past
> > intermediate frames which don't understand the protocol (i.e. no
> > throwing an exception and prematurely terminating them)?
>
> I don't know if this is sufficient for what you had in mind, but it's
> pretty close:
I was looking for something more functional, something without
explicit side effects. But maybe its just a figment of my not
sleeping last night (crazy deadline at work). Looking at the website,
I now read "Bindings created with binding can be assigned to, which
provides a means for nested contexts to communicate with code before
it the call stack." So this last question may have been wack.
But here's a follow on: How can I, without introducing temporary
variables, pass a bound variable back up to the parent binding?
e.g.
(binding [x nil y nil]
(binding [x 1 y 1]
; how to set the upper "x" to 1 or 2 or ...
))
or fleshed out as
(defn knows-protocol [x]
(set! side-x x)
(+ x 5))
(defn filter-protocol [fn x]
(binding [side-x nil side-y nil] ; capture the protocol so we can
selectively modify side-x and block side-y
(fn x)
(when (something side-x)
(set! side-x (+ 2 x))))) ; should modify the previous binding
(defn test []
(binding [side-x nil side-y nil]
(filter-protocol knows-protocol 5)
; I want side-x to be 7
))
I guess filter-protocol would be written as
(defn filter-protocol [fn x]
(let [local-x side-x]
(binding [side-y nil]
(fn x))
(if (something side-x)
(set! side-x (+ 2 x))
(set! side-x local-x))))
but this feels dirty.
Clojure's a new tool for me, and I'm kicking the tires trying to
figure out how it works.
Thanks,
Daniel
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