Question about `binding'

[Yang Dong]

(binding [inc dec]
(println (inc 1)))

;=> 2

If I put a declare on top of it,

(declare inc)

(binding [inc dec]
(println (inc 1)))

;=> 0

Originally I thought binding is equal to thread local dynamic binding.
Seems I was wrong. It seems like it has something to do with
namespaces. Right?

[CuppoJava]

Your original understanding is correct. Your first example is not
working the way you expect it because Clojure is inlining "inc" for
speed purposes.

Hope that helps
-Patrick

[Yang Dong]

That sounds reasonable. But how would you explain `pmap'? This
function is not inlined. In fact, every function in clojure.core can't
be bound without a declare (as far as I have tried). And it seems this
problem only exists when I tried to bind the core functions. It's ok
for me to substitute the functions in other namespaces.

[Michał Marczyk]

On 5 September 2010 07:48, Yang Dong <ydong....@gmail.com> wrote:
> That sounds reasonable. But how would you explain `pmap'? This
> function is not inlined. In fact, every function in clojure.core can't
> be bound without a declare (as far as I have tried). And it seems this
> problem only exists when I tried to bind the core functions. It's ok
> for me to substitute the functions in other namespaces.

When the compiler encounters a non-namespace-qualified symbol in the
code, it first resolves it to a Var. For example, the symbol 'inc
normally gets resolved to #'clojure.core/inc; however, after you
(declare inc) in the user namespace, it resolves to #'user/inc. Calls
going through Vars in clojure.core receive special treatment for
speed, which is why you can't rebind them.

Note that with the upcoming :static functions we'll all be free to
have our Vars behave this way (at a finer, per Var granularity level).

Sincerely,
Michał

[Phil Hagelberg]

On Sun, Sep 5, 2010 at 3:32 PM, Michał Marczyk <michal....@gmail.com> wrote:
> Calls going through Vars in clojure.core receive special treatment for
> speed, which is why you can't rebind them.

Actually this was backed out before 1.2 was released. Now only
definline functions and (in 1.3) static functions behave this way if I
remember correctly.

-Phil