Show HN: Writing an HTTP server in Prolog

http://jamesbvaughan.com/writing-an-http-server-in-prolog/

by jamesbvaughan • 10 years ago

238 70 10 years ago

dangoldin4• 10 years ago

Pretty cool.

I also did a stint messing around with Prolog and it was pretty awesome discovering an entirely new programming paradigm. I ended up doing the Priceonomics puzzle (https://priceonomics.com/jobs/puzzle/) in Prolog and wrote up about it here - http://dangoldin.com/2013/06/07/fun-with-prolog-priceonomics...

jamesbvaughan6• 10 years ago

That's awesome, thanks for sharing!

dangoldin4• 10 years ago

Yea - Prolog is super neat and gets you thinking a very different way. It was my first real introduction so took a bit of time getting used to thinking the "Prolog" way.

p4bl0• 10 years ago

This is really fun. Thanks for sharing!

jamesbvaughan6• 10 years ago

Thanks for reading!

aibottle• 10 years ago

No! What are you doing?! Let that language die in peace!

chriswarbo2• 10 years ago

Any particular reason you think Prolog should be abandoned?

I think it looks like very nice language for untyped, high-level programming.

dangoldin4• 10 years ago

My understanding is that there's a very limited amount of research going into Prolog so it ends up being incredibly slow for larger tasks. And a lot of it's functionality can be done via standard SQL so there's not a ton of use cases for it.

MrFeynmannsJoke• 10 years ago

Sometimes, just because you can doesn't mean you should..

chriswarbo2• 10 years ago

The author states many times that they did this to learn about networking and Prolog, killing two birds with one stone. This is clearly in no way meant to run any serious server software.

Are you saying that people shouldn't teach themselves powerful technologies?

coderdude• 10 years ago

Are you saying that people shouldn't teach themselves powerful technologies?

That much it was clear they weren't saying. What was being said was that prolog is just about the last lang you'd do this in. Aside from that, I think everyone else was aware that this was an experiment.

To add:

I think this is a great approach. The last highly up voted article suffered from being the same ol' hello world intro to prolog. It's fun to see a real world problem tackled.

nextos• 10 years ago

There is a revival of Datalog, a subset of Prolog, in relational databases and RAD. E.g., see LogicBlox or Datomic.

I always think Datalog should have taken a big chunk of SQL's market. And I wish something like Mozart/Oz was more mainstream so that we could implement subsystems using logic programming wherever needed.

faceyspacey2• 10 years ago

Chris Granger's Eve is based on Datalog. Perhaps his work is finally what breaks out the logic programming prolog paradigm.

rch• 10 years ago

Chris Granger is charismatic, but not particularly insightful. It would be better if he found a mentor.

pizza• 10 years ago

Machine Learning in Prolog https://www.cs.unm.edu/~luger/ai-final2/CH7_Machine%20Learni...

gnarbarian• 10 years ago

Prolog is extremely different than other programming languages and as a result, learning it and writing a few small programs is very mind expanding.

It really drives home how different paradigms are suited to different problems. Prolog is suited toward problems like Einsteins riddle

https://udel.edu/~os/riddle.html

jamesbvaughan6• 10 years ago

The class I was taking kind of blew my mind when I saw how you can solve some problems in such cool ways with Prolog, but I would certainly admit that this server isn't exactly the kind of use it's best suited for.

xapata3• 10 years ago

Python's set class and comprehension syntax can get you much of the declarative power of Prolog.

doublec• 10 years ago

You might be surprised! SWI Prolog has libraries for web applications (http://www.pathwayslms.com/swipltuts/html/index.html) and other modern application development toolkits. Their online IDE (http://swish.swi-prolog.org/) is written in Prolog.

rtpg• 10 years ago

A very interesting aspect of Prolog is how its primary primitive is backtracking search.

This is orders of magnitude more complex than C-language style primary primitives which closely match single machine instructions. Or even slightly more complex models in lazy languages like Haskell.

It's strange that you can build a language almost purely off of graph search yet have it be generally useful. Makes you wonder what other techniques spawn their own paradigm.

Allan_Smithee• 10 years ago

There's at least one language (Refal: there may be more!) based on Markov algorithms. Another language (XL: as far as I know this is the only one of its breed thus far) works at its core on parse tree substitution. Yet another (CHR) does a weird generalization of term re-writing to provide a toolkit for making constraint languages. (Yes, a language to make languages.)

There's a reason I've become a programming language whore.

hossbeast• 10 years ago

.pl is perl, use .pg for prolog

TheRealPomax• 10 years ago

or don't, because .pl is _also_ prolog and if you use something SWI Prolog, which is a windows executable, chances that you're still also using perl are preeeetty small.

gwu78• 10 years ago

Prolog predates Perl by 15 years.

cdmckay• 10 years ago

Where are you getting .pg from? Wikipedia lists .pl, .pro and .P as extensions.

mst2• 10 years ago

Amusingly perl's documentation says .pl is for a perl library and perl scripts should be .plx (for perl executable).

So nobody pays attention to that rule anyway.

I do get slightly confused switching between #perl and ##prolog on freenode sometimes, but the other regulars just laugh at me and we move on ;)

justinator• 10 years ago

This may be true in Perl 4, but hasn't been a rule in this century, I don't believe.

Spooky232• 10 years ago

In one of my first jobs out of college, I got assigned to figure out how to make the Tivoli Enterprise Console do something useful. They gave up on the IGS guys and picked me because I took a class that used Prolog in my sophomore year.

But it was a great time... a coworker and I came up with a way to persist facts to DB2 and decode/standardize all sorts of fubar network device alarms. Good times.

qohen• 10 years ago

The embedded Prolog was ProLog by BIM, from BIM Systems, which was the Belgian-based competitor to a US-based company called Quintus, in Mountain View; both offered high-end Prolog systems for Unix.

One of the things that ProLog by BIM had was the ability to have Prolog use Oracle or Sybase databases as if they were Prolog's own native database (Spooky23, if you see this, I was wondering if that helped you use DB2 in this fashion when doing your Tivoli work or did you roll your own from scratch?)

Anyway, Tivoli apparently created a macro language, TEC, that was then compiled down to Prolog to run.

Here's an opinionated look at TEC and the decision to use Prolog:

http://www.softpanorama.org/Admin/Tivoli/TEC/tec_rules_progr...

Some more info/perspectives from back-when about Tivoli's use of Prolog:

https://groups.google.com/forum/#!topic/comp.lang.prolog/LgM...

Spooky232• 10 years ago

Yes! Thanks for remembering!

Those BIM features were unknown to us as we had no BIM manuals. We took some open source code in a mailing list that let you dynamically load shared libraries. That's how we interacted with the DB2 client, and we also did a similar thing with Perl so the admins could do some work for us.

The IBM macro stuff was mostly there to power their (Motif based) rule builder GUI and was pretty limited unless you pre-processed events upstream and spoon fed it. That's why the IGS guys struggled -- they were certified against the base product (and had minimal experience beyond installing the thing) and the salespeople were aspirationally selling whatever one of the big financial services places did with the product.

It's been 15 years so I'm hazy but I'm pretty sure I tossed most of the macros that shipped with the product. It was a really fun gig and I learned a lot from it.

nickpsecurity4• 10 years ago

James, check out Mercury next as it's a faster, better Prolog with some industrial use.

https://mercurylang.org

jamesbvaughan6• 10 years ago

That looks really cool. To be honest I hadn't planned to use Prolog too much beyond this project, but I'll give Mercury a try if I decide to dive deeper into logic programming. Thanks!

cronjobber• 10 years ago

Last time I looked (admittedly years ago), it wasn't an unambiguously "better Prolog", because Mercury's static mode system couldn't capture all of what Prolog can do with unification.

nickpsecurity4• 10 years ago

I'm repeating what most users told me. This is a new one on me. Care to elaborate?

vram225• 10 years ago

I read that Prince XML (now called just Prince) was written in Mercury.

https://en.wikipedia.org/wiki/Prince_(software)

It's a software to generate PDF from XML and HTML content with CSS.

ga2arch• 10 years ago

Awesome, one of the most fun i had at university was building a Uri parser with prolog.

After i discovered that you could define operators i built a combinatorial parser, something akin to https://hackage.haskell.org/package/parsec (of course nowhere as powerful) with similar syntax and do notation. https://gist.github.com/ga2arch/e8904177f722c6560e37

And i didn't have to define backtracking because it is handled by prolog itself.

chatmasta2• 10 years ago

Have you learned about definite clause grammar yet? Once you do, you may be tempted to rewrite your parser, because it's a much more elegant way of constructing parsing rules.

jamesbvaughan6• 10 years ago

I have not learned about that, but I'm very interested now. Before I go and google it, do you have a specific place you'd recommend I go to learn about it?

chatmasta2• 10 years ago

Don't know... I took it in a class just like yours. IIRC it was the SWI prolog docs site

sleepprogger• 10 years ago

Site seem to be down. `Error establishing a database connection`

jamesbvaughan6• 10 years ago

I wasn't expecting so much traffic! It should be back up now.

Show HN: Writing an HTTP server in Prolog

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