Is there any way to get a variable address in Common Lisp?

Question

I'm trying to implement XOR-linked lists on Common Lisp, but i need to get an address of a variable to perform any bitwise operations on it. Is there any way to get memory address of a variable, similar to python's id() function?

Shavonneshaw

If you need low-level things like addresses, Common Lisp is not the right tool; but it is a very good tool for high-level programming. Why do you need XOR-linked lists in Lisp? – Aggappora

In Common Lisp addresses of variables make very little sense. Variables are often just pointers to objects. – Demagogic

Garbage collection can move things around,and some entire can be copied whenever the implementation wants. So there's no reliable sense of address for what you're trying to do. – Awad

You might find an unrolled linked list easier to implement in Common Lisp, with many of the same memory advantages. – Awad

@BasileStarynkevitch actually, i was trying to do it just for the sake of doing it. I was interested if this can be implemented in lisp, and how hard it is to implement. – Shavonneshaw

@RainerJoswig: I believe it is more appropriate to say that values are pointers to "objects" and variables contain such values – Aggappora

@JoshuaTaylor, I was trying to implement double-linked list, and as i saw it, xor-linked lists are a best way to implement using cons-cells. I guess i was wrong – Shavonneshaw

@BasileStarynkevitch: compare the definition of 'value' in Common Lisp: lispworks.com/documentation/HyperSpec/Body/26_glo_v.htm#value and also see variable under lispworks.com/documentation/HyperSpec/Body/… – Demagogic

Answer 1

Usually, memory management in Common Lisp is performed by some kind of Garbage Collector. Many of these algorithms move the objects in memory during a collection cycle.

So the consequencies are that you cannot count on a fixed address for each object, and for this reason no operation in the standard is provided to get the address of a Common Lisp object.

Precipitancy

Answer 2

If you're using Allegro Common Lisp, maybe this is what you're looking for: Escape from the Heap: Low-Level Programming in Common Lisp

Goring