I would like to change normal behavior of code
(def a 5)
(def b a)
(def a 1)
b
5
To this behavior
(def a 5)
(*something* b a)
(def a 1)
b
1
It is just for learning purposes so please do not try any deep sense in this.
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That's not how variables in Lisp family languages work.Barmar– Barmar2013-09-19 08:28:24 +00:00Commented Sep 19, 2013 at 8:28
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In Common Lisp you can do it with symbol macros. I googled and found this for you: github.com/clojure/tools.macroBarmar– Barmar2013-09-19 08:30:19 +00:00Commented Sep 19, 2013 at 8:30
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1Please, don't code in imperative style while you do functional programming.Chiron– Chiron2013-09-19 11:21:42 +00:00Commented Sep 19, 2013 at 11:21
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2 Answers
As an addition to Jared314's answer, I would like to point out that if you make a itself an atom or ref, b will automatically be something like a pointer or reference to a:
(def a (atom 5))
(def b a)
@b ;=> 5
(reset! a 1)
@b ;=> 1
Comments
When you redefine a, you are not changing the value of a like you would in another language. It might be better to think of a as a constant. You have created a new a. This is part of the design philosophy of Clojure.
If you want something like a pointer, take a look at refs and atoms.
Atom:
(def a 5)
(def b (atom a))
@b ;=> 5
(def a 1)
@b ;=> 5
(reset! b a)
@b ;=> 1
Ref:
(def a 5)
(def b (ref a))
@b ;=> 5
(def a 1)
@b ;=> 5
(dosync
(ref-set b a))
@b ;=> 1
Note: the @ is used to dereference b. It is shorthand for the deref function, and is required to get the value of b.
