Topic: How to determine equality of nesting

[Jeremy Dunn]

Let us say I want to determine if two expressions have the same form or not. I will call the function form= to write examples. Here are some examples to illustrate

(form= 3 (a b)) -> nil
(form= (a (b c)) (a b c)) -> nil
(form= (1 (2 3)) (5 (6 7))) -> T

So the idea is that expressions can be equal even if the individual elements are not and that only the number of elements and the nesting of the elements are important. Anyone have a function that can do this?

[gile]

Hi,

If the order of items matters
(foo '(1 (2 3)) '(5 (6 7))) return T
(foo '(1 (2 3)) '((6 7) 5)) return nil

Code - Auto/Visual Lisp: [Select]

1. (defun foo (a b)
2.   (or
3.     (and (atom a) (atom b))
4.     (and (listp a)
5.          (listp b)
6.          (= (length a) (length b))
7.          (vl-every 'foo a b)
8.     )
9.   )
10. )

If the order does not matter
(bar '(1 (2 3) (b)) '(5 (6 7) (9))) returns T
(bar '(1 (2 3) (b)) '(5 (9) (6 7))) returns T

Code - Auto/Visual Lisp: [Select]

1. (defun bar (a b)
2.   (or
3.     (and (atom a) (atom b))
4.     (and (listp a)
5.          (listp b)
6.          (= (length a) (length b))
7.          (vl-every 'bar
8.                    (vl-sort (vl-remove-if 'atom a) '(lambda (x y) (< (length x) (length y))))
9.                    (vl-sort (vl-remove-if 'atom b) '(lambda (x y) (< (length x) (length y))))
10.          )
11.     )
12.   )
13. )

[myloveflyer]

Hi,

If the order of items matters
(foo '(1 (2 3)) '(5 (6 7))) return T
(foo '(1 (2 3)) '((6 7) 5)) return nil

Code - Auto/Visual Lisp: [Select]

1. (defun foo (a b)
2.   (or
3.     (and (atom a) (atom b))
4.     (and (listp a)
5.          (listp b)
6.          (= (length a) (length b))
7.          (vl-every 'foo a b)
8.     )
9.   )
10. )

If the order does not matter
(bar '(1 (2 3) (b)) '(5 (6 7) (9))) returns T
(bar '(1 (2 3) (b)) '(5 (9) (6 7))) returns T

Code - Auto/Visual Lisp: [Select]

1. (defun bar (a b)
2.   (or
3.     (and (atom a) (atom b))
4.     (and (listp a)
5.          (listp b)
6.          (= (length a) (length b))
7.          (vl-every 'bar
8.                    (vl-sort (vl-remove-if 'atom a) '(lambda (x y) (< (length x) (length y))))
9.                    (vl-sort (vl-remove-if 'atom b) '(lambda (x y) (< (length x) (length y))))
10.          )
11.     )
12.   )
13. )

Gile,Nice Work!

[Lee Mac]

Nice code gile 

Here's an alternative to allow for dotted pairs -

Code - Auto/Visual Lisp: [Select]

1. (defun foo ( a b )
2.     (or (and (atom  a) (atom  b))
3.         (and (listp a) (listp b)
4.              (= (vl-list-length a) (vl-list-length b))
5.              (foo (car a) (car b))
6.              (foo (cdr a) (cdr b))
7.         )
8.     )
9. )

Code - Auto/Visual Lisp: [Select]

1. _$ (foo 1 1)
2. T
3. _$ (foo 1 '(1))
4. nil
5. _$ (foo 1 '(1 . 1))
6. nil
7. _$ (foo '(1) '(1))
8. T
9. _$ (foo '(1) '(1 . 1))
10. nil
11. _$ (foo '(1 . 1) '(1 . 1))
12. T

[bruno_vdh]

Hello,
Maybe I do not understand the subject, but why?

_$ (foo '(1) '(1 . 1))
nil

If we consider this:

Code: [Select]

_$ (car '(1.1))
1.1
_$ (car '(1))
1
_$ (cdr '(1.1))
nil
_$ (cdr '(1))
nil

So this definition seems to me preferable ...

Code: [Select]

(defun f (a b)
  (cond
    ((atom a) (atom b))
    ((atom b) nil)
    ((f (car a) (car b)) (f (cdr a) (cdr b)))
  )
)


Code: [Select]

_$ (f 1 1)
T
$ (f 1 '(1))
nil
_$ (f 1 '(1 . 1))
nil
_$ (f '(1) '(1 . 1))
T
_$ (f '(1 . 1) '(1 . 1))
T


[Lee Mac]

_$ (foo '(1) '(1 . 1))
nil

If we consider this:

Code: [Select]

_$ (car '(1.1))
1.1
_$ (car '(1))
1
_$ (cdr '(1.1))
nil
_$ (cdr '(1))
nil


'(1 . 1) is very different to '(1.1) - the former represents a dotted pair, the latter a list containing a single item.

As such, the comparison would become:

Code - Auto/Visual Lisp: [Select]

1. _$ (car '(1 . 1))
2. 1
3. _$ (car '(1))
4. 1
5. _$ (cdr '(1 . 1))
6. 1
7. _$ (cdr '(1))
8. nil

[bruno_vdh]

Yes I was too fast in my conclusions, thanks for correcting my mistake