prolog | Automated Logger and Interactive Console for Unity | Game Engine library

is/2is a buildin predicate that requires that the second argument is a term that is arithmetically resolvable (examples: 3+6, 7*3).

In your example, you use NewList is [H, Newlist1] where the second argument is a list and not an arithmetic expression. Therefore you get a type error. You should use the matching operator = instead.

The second problem with your code is that [H, Newlist1] builds up a nested list (it is a list of length 2, the first element is H and the second is the list Newlist1. Here is the corrected version of your code:

Maybe this example will help (it uses a "lattice" rather than "min", but they're similar; and if you're doing edit distance, you might want to keep a list of the edits anyway): https://www.swi-prolog.org/pldoc/man?section=tabling-mode-directed

"In this execution model one or more arguments are not added to the table. Instead, we remember a single aggregated value for these arguments."

Is this true in all cases, or can more intricate examples be constructed where unification would still recurse infinitely?

AFAIK no.

I can't recall seeing where =/2 did not work as expected. Granted my expectations are of how SWI-Prolog does =/2 as noted below.

As a related side-question, why does (again, I used swi-prolog) unification binds X to Y in the following example? I didn't expect that.

See these comments in the SWI-Prolog C code for cyclic terms.

There are several problems here.

Problem 1 is that the non-recursive clauses for your recursive predicates look like this:

Is that possible?

No, unfortunately, it isn't, because XML functions like XMLTable work with XMLType which parses your input xml (from your NLS_LANG charset if it is CLOB or Varchar2, and from specified charset if it is BLOB) and store it in own internal codepage and when you get it, oracle returns it in your NLS_LANG:

I think the Prolog code is a distraction. Since, as you say, Datalog doesn't support lists and other Prolog terms apart from atoms and variables, trying to go through Prolog doesn't seem helpful.

That said, your Prolog code is also not very well written. The language allows you to write what appears to be a single nullable/1 predicate that deals with symbols, productions, and rules. But that doesn't make it a good idea. You will also make yourself very unhappy by giving variables for lists unhelpful names like Y. A common convention is to add an s suffix to variable names for lists. Here is a cleaner version of your Prolog code:

Pure Prolog conjunctions and disjunctions are, in fact, commutative and associative.

This allows us to ignore clause and goal order, provided that all answer sequences are finite.

When queries have infinite solution sets, Prolog may need to systematically enumerate infinite answer sequences.

To help Prolog find answers for above “problematic” queries, swap the two recursive rules:

The first question must be why? A failure-slice helps to understand the problem:

When discussing various versions of the same program, it helps a lot to rename those versions such that they can cohabit in the same program: