Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Another way to do that is to create a new kind of object which is like
> a spreadsheet-cell: it comes with an expression to compute it, and
> remembers its current value.  Internally it also keeps track of the
> other spreadsheet-cells used during the computation of the current
> value (i.e. the dependencies are automatically tracked for you).
>
> You also get to choose whether to check the current value's validity
> lazily (like you do in your code), or to eagerly mark dependencies
> "dirty" when a cell is modified.

I think I've got that working - see attachment (though I chose different
function names).

Of course we want a gv-setter for `sscell-get'!  A surprising side
effect of this is that, contrary to thunk-let, sscell-let bound
variables suddenly get settable, e.g.

#+begin_src emacs-lisp
(sscell-let ((x () 1))
  (let ((y 7))
    (setq x (+ x y))
    (* 10 x)))
==> 80
#+end_src


Michael.