Let bindings map pretty much directly to Java style local variables:
(let [x 42]
(let [x 3]
(+ x 3))
Becomes something like this when compiled to byte code:
x_1 = 42
x_2 = 3
return x_2 +3
So let bindings with the same names are kept separate via modifying the
stored name in the byte code, and these local variables are never
overwritten except via a loop. Let bindings in Clojure are not "reified"
(not something you can reference), they are simply names for calculated
values. Contrast this with a var.
Vars however are reified. You can look at a var in Clojure:
(def foo 42)
#'foo
=> <Var ...>
(deref #'foo)
=> 42
The #' reader macro says "get me the var with this name, but don't call
deref on it; I want the actual var". That's not something you can do with
let bindings since they are not a first class object in the language.
Timothy
On Sat, Dec 3, 2016 at 10:06 PM, Paul Gowder <paul.gow...@gmail.com> wrote:
> That's a really neat post. Thank you for writing it!
>
> How do bindings created by let fit into that picture?
>
> The question of how vars work comes up enough that I recently wrote a blog
> post on the subject. Maybe it will be useful to you.
> http://blog.cognitect.com/blog/2016/9/15/works-on-my-
> machine-understanding-var-bindings-and-roots
>
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