[cells-devel] Added cells-store to cells

[Peter Hildebrandt]

As promised yesterday I added a cells-store facility to cells.   The
code can be found at the bottom of md-utilities in CVS.

Basically, this is a cells-aware hash table with some syntactic sugar.

Here's part of the test function included in md-utilities:

(defun test-cells-store ()
  (trc "testing cells-store -- making objects")
  (let* ((store (make-instance 'cells-store))
	 (foo (make-instance 'test-store-item :value (c?-with-stored (v :foo
store 'nothing)
						       (bwhen (val (value v)) val))))
	 (foo+1 (make-instance 'test-store-item :value (c?-with-stored (v
:foo store 'nothing)
							 (bwhen (val (value v)) (1+ val))))))
    (store-add :foo store (make-instance 'family :value (c-in nil)))

    (setf (value (store-lookup :foo store)) 1)

   (store-remove :foo store))

So you create a ruled cell with c?-with-stored.   This can happen
before or after key is added to the cells-store.  When the rule is the
executed, when an object is added or removed from key in the hash
table *or* when any of the cells on the object change.  The rule is
not executed, if other stuff in the hash table changes.

The (c?-with-stored (var key store &optional default) &body body)
macro works like bwhen -- that is, if key is present, body is executed
with var bound to the object identified by key --  and if not, default
is returned.  That means, body can assume that var is bound to a valid
object (like in the example, it is safe to call value on it, if you
know that you only store family instances in the store)

Calling store-remove will reset all dependent cells to their default.

The change is propagated as soon as store-add, setf, or store-remove
are called -- meaning that observers will do the expected thing.

Maybe someone will find it useful.

Peter