[ACT-R-users] New ACT-R 6.0 release

[db30 at andrew.cmu.edu]

ACT-R 6.0 v1.5 [r1395] is now the current version on the ACT-R web site.

Here are the significant changes from the previous version:

- There is now a whynot-dm command that is similar to the whynot command.
It compares chunks from declarative memory to the most recent retrieval
request that occurred and reports why those chunks were or were not
chosen to be retrieved.


- Added the ability to pass request parameters when making a direct
request in a production by putting the chunk and the request parameters
in a list:

(p direct-request-with-parameters
  =retrieval>
    isa visual-location
 ==>
  +visual-location> (=retrieval :attended nil))


- Productions now allow slots which exist in a subtype of a chunk-type to
be specified under an isa test of the parent type in both the conditions
and actions.  Specifying a slot in a condition which does not exist in the
type named in the isa test adds an implicit test that the chunk in the
buffer have such a slot.

Here is an example of a production which was not allowed previously but
is allowed now:

(chunk-type parent)
(chunk-type (child (:include parent)) slot)

(p use-child-slot
  =goal>
    isa parent
    slot =x
  ==>
  =goal>
    slot nil
  +retrieval>
    isa parent
    slot nil)


- Added an alternate mechanism for extending chunks.  Instead of extending
the chunk-type and thus adding the new slots to every chunk of that type,
the new mechanism works by creating new subtypes for each combination of
slots that get added to a chunk-type.  It then changes the chunk-type of
an extended chunk to match the appropriate subtype.  It also allows for
removing extended slots from a chunk by setting them to nil, which will
also lead to a change in the type of the extended chunk.  When using the
new mechanism, an extended chunk will only have the extended slots which
contain values.

To use the new mechanism the type that is going to be extended must be
declared as static when creating the chunk-type:

(chunk-type (type-name (:static t)) ...)

To go along with that change, the way productions handle a test for
"<slot> nil" when the chunk in the buffer is of a static chunk-type has
been changed.  Such a condition will be true if the chunk does not have
such a slot.

Additional details on this new mechanism can be found in the "Static Type
Mechanism" section of the reference manual.


For details on what else has changed, you can view the commit log on the
ACT-R web site:

<http://act-r.psy.cmu.edu/~webcron/actr6log.txt>

You can also subscribe to a feed to be notified of every change to the
sources:

<http://act-r.psy.cmu.edu/~webcron/actr6feed.xml>

I will be discussing these changes in detail at the 2013 ACT-R Workshop.

If you have any comments, questions, or problems with this update please
let me know.

Dan