RE: [External] : Re: Hash consing (was: Re: sqlite3)

[Drew Adams]

> > some kind of immutable cons data type.
> We already have that: for example, the result of evaluating the form '(1 .
> 2) is an immutable cons cell.  The immutability isn't enforced, though:
> passing such a cons cell to `rplaca' will cause undefined behavior, but
> typically not signal an error.

Sorry, but I don't understand what you're saying.
What's immutable about it?  What's undefined
about using `setcar' or `rplaca' on it?
 (setq x '(1 . 2))
 (setcar x 3)