[refset]

The dissertation covers extensive details, but on your last point at least it describes:

> 2.2.1 Evaluation by Default. One of the major syntactic differences between Dyna and other logic programming languages is that Dyna evaluates an expression in place by default. The reason for this change is that most terms have a meaningful value, much like how a function returns a value in a functional programming language. Conversely, in logic programming languages such as Prolog or Datalog, terms only “return” the value of true.

[YeGoblynQueenne]

Prolog (and Datalog) plays fast and loose with the original FOL terminology from which its own is derived, so e.g. a "term" in Prolog is both an "atomic formula" or "atom" in FOL, and a "first order term" (or just term) in FOL. In FOL the sets of function and predicate symbols are distinct and disjoint, but in Prolog they are not, and my guess has always been that this is the reason that everything gets called a "term" (and "atom" ends up replacing "constant").

And nothing gets evaluated, either in FOL or Prolog/Datalog, so I'd like to nitpick and say that terms don't '"return" the value of true', they are only transformed, by unification and -in the case of Prolog- by SLD-Resolution. The interpretation of a Prolog program eventually "returns" the result of a proof, which is usually 'true' or 'false', but sometimes 'yes' or 'no'; but nothing in a Prolog program can really be seen as "returning" anything. It's a peculiarity of logic programming languages that I think takes a while for most programmers to get their heads around.

So a logic programming language that returns values and replaces expressions by their values is a substantial departure from Prolog syntax and semantics. But, you know that judging from the excerpt above.

Pedantry!

[tannhaeuser]

It's not pedantic at all. Interpreting terms as "themselves" and term ordering is core to Herbrand interpretation and unification, as you know very well.

[YeGoblynQueenne]

Yes but not everyone is up for a logic programming lecture on a Sunday :)