Kevin Wortman scripsit:

> How about something like this (untested pseudocode) for alist->bag!:
>
> (define (alist->bag! bag alist)
>   (bag-delete-all! bag (map car alist))

Bag-delete-all doesn't remove all instances of the objects in the list,
only one instance: it means "all in list", not "all copies".  Maybe the
name should be changed?  And by the same token, maybe there should be
bag operations to delete all copies of some object(s)?

>   (for-each (lambda (pair)
>                   (unless (bag-contains? bag (car pair))
>                     (bag-increment! bag (car pair) (cdr pair))))
>                 alist))

That's what I said it should do, but on reflection it's not quite right.
If the bag is {a, a, a} and the a-list says ((a . 1) (a . 2)), I think
we should end up with {a, a, a, a} as a result of the (a . 1), and the
(a . 2) should be ignored.

Maybe this means that alist->bag! doesn't really make sense.  Thoughts?

--
John Cowan          http://www.ccil.org/~cowan        xxxxxx@ccil.org
Principles.  You can't say A is made of B or vice versa.
All mass is interaction.  --Richard Feynman