Hi, Tim,
I'm not 100% certain what is going on here, but I do know that, in
general, binding and loop/recur should not be mixed.
"recur" is not true recursion -- it's more like a GOTO. The "binding"
macro establishes thread-local bindings using the static methods
clojure.lang.Var/pushThreadBindings and popThreadBindings. So what I
think is happening in your first example is that the "recur" jumps
back to the top of the loop before "popThreadBindings" gets called.
I have no idea why it only happens three times, or why it doesn't
happen in your second example.
Here's a demonstration:
user> (loop [x 0]
(println "x" x)
(binding [y (inc y)]
(println "y" y)
(if (< x 10) (recur (inc x)))))
x 0
...
user> y
3
user> (clojure.lang.Var/popThreadBindings)
nil
user> y
2
user> (clojure.lang.Var/popThreadBindings)
nil
user> y
1
user> (clojure.lang.Var/popThreadBindings)
nil
user> y
0
user>
-SS
On Jul 17, 10:38 pm, Tim Snyder <[email protected]> wrote:
> I was experimenting with how binding behaves within a loop and found
> some inconsistent results:
>
> (def y 0)
> (loop [x 0]
> (println "x " x)
> (binding [y (inc y)]
> (println "y " y)
> (if (< x 10) (recur (inc x)))))
>
> The printed lines are what you'd expect:
> x 0
> y 1
> x 1
> ...
> x 10
> y 11
>
> But if you then check the value of y afterwards, it is 3. Each time
> the above loop is executed, y goes up by another 3. I'm not sure how
> I can see the whole stack of bound values, but I did confirm the root
> is still 0.
>
> Oddly, the following /does not/ result in left-over bindings:
> (loop [x 5]
> (binding [y (inc y)]
> (println "x " x ", y " y)
> (if (> x 0) (recur (dec x)))))
>
> Any ideas on the differences?
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