Nell/Prolog

CSA: I did a lot of research on Prolog and Prolog-related topics. The bottom line is that it's probably not directly relevant for our project: what we really need is an incremental planner or a truth maintenance system, not a backtracking solver. Prolog doesn't come with any magic bullets to answer the "now what goals have their preconditions satisfied" question, which is at the core of a UNIVERSE-style storytelling system.

Datalog might still be interesting as a data model for "avatar services".

Interesting Prologs

• Prolog Syntax and Semantics from wikipedia.
• Datalog
• Logtalk (wiki) -- the object oriented features provide a good encapsulation mechanism for a prolog-style language. It also supports "event-driven programming"; I can't tell if that would help one construct a truth maintenance system (ie, track dependencies) or not.
• JScriptLog: implementation of ISO-Standard PROLOG in JavaScript. Seems pretty capable, but the code is not the cleanest -- no attempt at using prototypes or object-orientation. Parser is apparently weak.
• Yield Prolog: an embedding of Prolog control flow into JavaScript using the yield operator. (See https://github.com/cscott/jsshaper for an implementation of yield for non-Firefox browsers.) Contains a compiler to translate 'standard' prolog into yield-using JavaScript (or Python, etc). The parser is original DEC-10 PROLOG and the compiler is also written in prolog, translated into yield-JavaScript, so the implementation must be fairly complete. I'm not 100% convinced it handles the various cut cases correctly. Also, modules in prolog are a mess (see Logtalk for a better solution), although there is some sort of module system implemented.
  • Would be interesting to port Logtalk to run on top of Yield Prolog, although I'm not sure how useful the result would be. Seems like a rather esoteric tower to build software for kids with.
• Warren's Abstract Machine (wiki) -- underlying virtual machine for many early Prologs. Worth digging through to get an idea of how Prolog is implemented.
• Pyke is an implementation of Prolog ideas for Python. I'm not thrilled with this; the embedding doesn't seem very elegant. Here's a brute-force (ie, "the wrong way to do it") solution to the Towers of Hanoi puzzle in Pyke: http://pyke.hg.sourceforge.net/hgweb/pyke/pyke/file/cc6970acfcf1/examples/towers_of_hanoi/towers2.krb

Truth Maintenance / Planners

• STRIPS

Storytelling

• UNIVERSE
  • 1984 paper, xxx, 19xx paper
  • Blog posts comparing it to MINSTREL

Natural Language Processing

Prolog and DCGs (Prolog's version of the Monad) are a pretty good way to tackle some natural language processing tasks.

• Natural Language Processing in Prolog

Adventure

• An adventure game in Logtalk: http://trac.logtalk.org/browser/trunk/examples/adventure/sleepy.lgt
• Another adventure in standard prolog, presented as a tutorial: http://www.amzi.com/AdventureInProlog/advtop.php (final code in http://www.amzi.com/AdventureInProlog/appendix.php if you're impatient)