generating SXML trees in guile

[Matt Wette <matt.wette@gmail.com>]

This is a FYI, not saying this is a bug.

I'm digging into the sxml xpath procedures and came across a potential
issue with using sxml in Guile.

I believe I remember that Oleg's SXML code relies on the fact that no
nodes a sxml tree are eq?.   For example, in the SXML tree

     (define sx1  '(*TOP* (a "1") (a "1)))

node-parent in (sxml xpath) depends on the fact that

     (eq? (list-ref sx1 1) (list-ref sx1 2)
=>
     #f

But the result, in Guile 3.0.4, is
     #t

I'm guessing this is cse optimization at work.  I tried this also:

(let* ((sx2 '())
        (sx2 (cons '(a "1") sx2))
        (sx2 (cons '(a "1") sx2))
        (sx2 (cons '*TOP* sx2)))
   (eq? (list-ref sx2 1) (list-ref sx2 2)))
=>
#t

In my sandbox, I'm using copy-tree which seems to be changing
the #t to #f, so at least that works.

Matt