Metaprogramming and syntax checking...

[rpgoldman]

I added a tentative check for ill-formed add and delete lists, but it fails the tests because of operators like these:

 (:op (!!assert ?fact)
  :add (?fact))

 (:op (!!delete ?fact)
  :delete (?fact))

These are from the Openstacks domain, but there are many like it.

I can think of at least a couple of possibilities:

1. Make !!assert and !!delete (and also = for "unifies") be built-ins.
2. Add some kind of meta-op declaration to tell SHOP that it shouldn't check the preconditions, add- or delete-lists for proper syntax. This could be as simple as permitting :meta t to appear in the body of an :op definition.

I'd like to find a solution, so that we can be more aggressive in checking for ill-formed operators.

/cc @ukuter