[alicebot-archcomm] <set> and unsetting them

[Dirk Scheuring]

Dr. Rich Wallace wrote:

> I would say, set to the empty string.

This doesn't really fit with the fact that the predicate content is
defined as an AIML pattern, which is defined as one or more words ("*"
not having standard 'Kleene star' semantics has been an issue here
before). At least according to the spec, you shouldn't be able to test

<condition name="foo" value="">

since there is no "empty string" in AIML. I find this unfortunate, but
that's the way you wanted it, and it's too late to change now without
breaking lots.

The way I write it is that there always has to be a default value, and
code that "consumes" some predicate value has to replace it with the
default. I thought that Pandorabots works like this, too - they don't
let you test for the empty string, but for a default "OM" value.

Dirk