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Learn Prolog Now (2006)

lpn.swi-prolog.org

41–50 of 251 posts

Re: Learn Prolog Now (2006)

#41

I remember writing a Prolog(ish) interpreter in Common Lisp in an 90's AI course in grad school for Theorem proving (which is essentially what Prolog is doing under the hood). Really foundational to my understanding of how declarative programming works. In an ideal world I would still be programming in Lisp and using Prolog tools.

> In an ideal world…

I see this sentiment a lot lately. A sense of missed nostalgia.

What happened?

In 20 years, will people reminisce about JavaScript frameworks and reminisce how this was an ideal world??

Re: Learn Prolog Now (2006)

#43

I really enjoyed learning Prolog in university, but it is a weird language. I think that 98% of tasks I would not want to use Prolog for, but for that remaining 2% of tasks it's extremely well suited for. I have always wished that I could easily call Prolog easily from other languages when it suited the use case, however good luck getting most companies to allow writing some code in Prolog.

That is where Lisp or Scheme weirdly shines. It is incredibly easy to add prolog to a Lisp or a Scheme. It’s almost as if it comes out naturally if you just go down the rabbit hole. “The little prover” is a fantastic book for that. The whole series is.

I worked through the little scheme but not the little prover, I think Ill take a look at that. Thanks.

Re: Learn Prolog Now (2006)

#44

I remember writing a Prolog(ish) interpreter in Common Lisp in an 90's AI course in grad school for Theorem proving (which is essentially what Prolog is doing under the hood). Really foundational to my understanding of how declarative programming works. In an ideal world I would still be programming in Lisp and using Prolog tools.

> In an ideal world… I see this sentiment a lot lately. A sense of missed nostalgia. What happened? In 20 years, will people reminisce about JavaScript frameworks and reminisce how this was an ideal world??

I can tell you, from the year 2045, that running the worlds global economy on Javascript was the direct link to the annihilation of most of our freedom and existence. Hope this helps.

Re: Learn Prolog Now (2006)

#46

is prolog a use-case language or is it as versatile as python?

FWIK; You can't compare the two. Python is far more general and larger than Prolog which is more specialized. However there have been various extensions to Prolog to make it more general. See Extensions section in Prolog wikipedia page - https://en.wikipedia.org/wiki/Prolog#Extensions Eg. Prolog++ - https://en.wikipedia.org/wiki/Prolog%2B%2B to allow one to do large-scale OO programming with Prolog.

Earlier, Prolog was used in AI/Expert Systems domains. Interestingly it was also used to model Requirements/Structured Analysis/Structured Design and in Prototyping. These usages seems interesting to me since there might be a way to use these techniques today with LLMs to have them generate "correct" code/answers.

For Prolog and LLMs see - https://news.ycombinator.com/item?id=45712934

Some old papers/books that i dug up and seem relevant;

Prototyping analysis, structured analysis, Prolog and prototypes - https://dl.acm.org/doi/10.1145/57216.57230

Prolog and Natural Language Analysis by Fernando C. N. Pereira and Stuart M. Shieber (free digital edition) - http://www.mtome.com/Publications/PNLA/pnla.html

The Application of Prolog to Structured Design - https://www.researchgate.net/publication/220281904_The_Appli...

Re: Learn Prolog Now (2006)

#47

is prolog a use-case language or is it as versatile as python?

Do you mean Northern Conservative Baptist Great Lakes Region Council of 1879 standard Prolog?[2]

SWI Prolog (specifically, see [2] again) is a high level interpreted language implemented in C, with an FFI to use libraries written in C[1], shipping with a standard library for HTTP, threading, ODBC, desktop GUI, and so on. In that sense it's very close to Python. You can do everyday ordinary things with it, like compute stuff, take input and output, serve HTML pages, process data. It starts up quickly, and is decently performant within its peers of high level GC languages - not v8 fast but not classic Java sluggish.

In other senses, it's not. The normal Algol-derivative things you are used to (arithmetic, text, loops) are clunky and weird. It's got the same problem as other declarative languages - writing what you want is not as easy as it seemed like it was going to be, and performance involves contorting your code into forms that the interpreter/compiler is good with.

It's got the problems of functional languages - everything must be recursion. Having to pass the whole world state in and out of things. Immutable variables and datastructures are not great for performance. Not great for naming either, temporary variable names all over.

It's got some features I've never seen in other languages - the way the constraint logic engine just works with normal variables is cool. Code-is-data-is-code is cool. Code/data is metaprogrammable in a LISP macro sort of way. New operators are just another predicate. Declarative Grammars are pretty unique.

The way the interpreter will try to find any valid path through your code - the thing which makes it so great for "write a little code, find a solution" - makes it tough to debug why things aren't working. And hard to name things, code doesn't do things it describes the relation of states to each other. That's hard to name on its own, but it's worse when you have to pass the world state and the temporary state through a load of recursive calls and try to name that clearly, too.

This is fun:

    countdown(0) :-
      write("finished!").   

    countdown(X) :-
      writeln(X),
      countdown(X-1).
    
It's a recursive countdown. There's no deliberate typos in it, but it won't work. The reason why is subtle - that code is doing something you can't do as easily in Python. It's passing a Prolog source code expression of X-1 into the recursive call, not the result of evaluating X-1 at runtime. That's how easy metaprogramming and code-generation is! That's why it's a fun language! That's also how easy it is to trip over "the basics" you expect from other languages.

It's full of legacy, even more than Python is. It has a global state - the Prolog database - but it's shunned. It has two or three different ways of thinking about strings, and it has atoms. ISO Prolog doesn't have modules, but different implementations of Prolog do have different implementations of modules. Literals for hashtables are contentious (see [2] again). Same for object orientation, standard library predicates, and more.

[1] https://www.swi-prolog.org/pldoc/man?section=foreign

[2] https://news.ycombinator.com/item?id=26624442

Re: Learn Prolog Now (2006)

#48
There seems to an interesting difference between Prolog and conventional (predicate) logic.

In Prolog, anything that can't be inferred from the knowledge base is false. If nothing about "playsAirGuitar(mia)" is implied by the knowledge base, it's false. All the facts are assumed to be given; therefore, if something isn't given, it must be false.

Predicate logic is the opposite: If I can't infer anything about "playsAirGuitar(mia)" from my axioms, it might be true or false. It's truth value is unknown. It's true in some model of the axioms, and false in others. The statement is independent of the axioms.

Deductive logic assumes an open universe, Prolog a closed universe.

Re: Learn Prolog Now (2006)

#49
post #33

Prolog really is such a fantastic system, if I can justify its usage then I won't hesitate to do so. Most of the time I'll call a language that I find to be powerful a "power tool", but that doesn't apply here. Prolog is beyond a power tool. A one-off bit of experimental tech built by the greatest minds of a forgotten generation. You'd it find deep in irradiated ruins of a dead city, buried far underground in a bunke…

When I entered university for my Bachelors, I was 28 years old and already worked for 5 or 6 years as a self-taught programmer in the industry. In the first semester, we had a Logic Programming class and it was solely taught in Prolog. At first, I was mega overwhelmed. It was so different than anything I did before and I had to unlearn a lot of things that I was used to in "regular" programming. At the end of the cla…

Did they teach you how to use DCGs? A few months ago I used EDCGs as part of a de-spaghettification and bug fixing effort to trawl a really nasty 10k loc sepples compilation unit and generate tags for different parts of it. Think ending up with a couple thousand ground terms like:

tag(TypeOfTag, ParentFunction, Line).

Type of tag indicating things like an unnecessary function call, unidiomatic conditional, etc.

I then used the REPL to pull things apart, wrote some manual notes, and then consulted my complete knowledgebase to create an action plan. Pretty classical expert system stuff. Originally I was expecting the bug fixing effort to take a couple of months. 10 days of Prolog code + 2 days of Prolog interaction + 3 days of sepples weedwacking and adjusting the what remained in the plugboard.

Re: Learn Prolog Now (2006)

#50

I am once again shilling the idea that someone should find a way to glue Prolog and LLMs together for better reasoning agents. https://news.ycombinator.com/context?id=43948657 Thesis: 1. LLMs are bad at counting the number of r's in strawberry. 2. LLMs are good at writing code that counts letters in a string. 3. LLMs are bad at solving reasoning problems. 4. Prolog is good at solving reasoning problems. 5. ??? 6. LLM…

> LLMs are bad at counting the number of r's in strawberry.

This is a tokenization issue, not an LLM issue.

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