On Wednesday, 3 April 2013 00:39:25 UTC+5:30, larry google groups wrote:
>
>
> If Clojure is suppose to emphasize immutability, why can I do this:
>
> kiosks-clojure.core=> (let [
> #_=> mega (+ 1 1)
> #_=> mega (+ 1 mega)
> #_=> mega (+ 1 mega)
> #_=> mega (+ 1 mega)
> #_=> mega (+ 1 mega)]
> #_=> mega)
> 6
>
> I might as well be writing PHP code.
>
In PHP and other imperative language `mega` is a "place" (as in place
oriented programming.) Consider this:
(let [mega 0]
(let [mega (+ 1 mega)]
(println mega))
(println mega))
Output:
1
0
In Clojure a symbol is bound to a value (both are otherwise independent) in
a scope. Bindings can nest and unwind like a stack. In PHP a variable is
tied to the "place" that can be updated but cannot nest. So, consider this
PHP snippet:
$mega = 0;
$mega = 1 + $mega;
echo $mega; // prints 1
echo $mega; // still prints 1 because it didn't unwind
When we say
(let [foo 20
foo (+ 5 foo)]
..)
we basically rebind within the same let form and it's a convenience to
rebind a local to a new value due to intermediate computation step.
Shantanu
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