Why Learn Prolog in 2021?

• core.logic

  8 1,432 5.2 Clojure

  A logic programming library for Clojure & ClojureScript

  

related:

https://github.com/clojure/core.logic/wiki/A-Core.logic-Prim...

• awesome-prolog

  1 474 0.0

  Curated list of Prolog packages and resources

Here are some resources:

https://github.com/klaussinani/awesome-prolog#resources

I recall going through the Adventure in Prolog one (free online resource) a while ago and enjoying it, helped direct a lot of exploration into the Prolog language and its capabilities for me. I have Clocksin & Mellish's Programming in Prolog (2003, 5th ed.) and liked it as a good introduction (or more expansion, I had dabbled in it previously and "knew" the language but not the full depth of it). I've read good things about The Art of Prolog by Sterling and Shapiro, but have not read it.

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• hatlog

  1 1 0.0 Python

  custom type systems for python in prolog: http://alehander42.me/prolog_type_systems

A couple years ago I hacked on a Python type inferencer someone wrote in Prolog. I wasn't enlightened, despite expecting to be, from a bunch of HN posts like this.

https://github.com/andychu/hatlog

For example, can someone add good error messages to this? It didn't really seem practical. I'm sure I am missing something, but there also seemed to be a lot of deficiencies.

In fact I think I learned the opposite lesson. I have to dig up the HN post, but I think the point was "Prolog is NOT logic". It's not programming and it's not math.

(Someone said the same thing about Project Euler and so forth, and I really liked that criticism. https://lobste.rs/s/bqnhbo/book_review_elements_programming )

• pyswip

  5 441 0.0 Python

  PySwip is a Python - SWI-Prolog bridge enabling to query SWI-Prolog in your Python programs. It features an (incomplete) SWI-Prolog foreign language interface, a utility class that makes it easy querying with Prolog and also a Pythonic interface.

It might be easier to learn prolog, if it's wrapped in more familiar python.[1] Prolog's value lies in its database core. But much of the cost of learning a language is elsewhere, in coping with yet another way to do familiar things. With prolog, these are both relatively uninteresting, and nicely separable.

[1] https://github.com/yuce/pyswip

• mercury

  2 874 9.8 Mercury

  The Mercury logic programming system. (by Mercury-Language)

  

I'm not convinced there's great utility in smart contracts, but if there is, I think there's a huge utility in contracts being declarative and statically typed, to avoid many of the problems we've seen with existing contracts. In that case, a statically typed Prolog dialect would be a good starting point. The contract would be a set of declarative rules describing acceptable next states of the contract. To make the contracts verifiable in linear time, the submitter would submit the next state of the contract, plus a compact binary representation of the path taken through the rules set, so no backtracking would occur in the verifier. You could allow recursion, as verification time would still be linear in the size of the submitted compact path representation, just not linear in the size of the contract. If you disallow recursion, then verification would also be linear in the size of the contract.

Granted, many of the problems with Ethereum Solidity contracts are more to do with all of its use of implicit behavior (in a misguided attempt to hide the complexity of contracts) rather than directly consequences of Solidity being imperative.

Here's a quick plug for Mercury[0], a statically typed dialect of Prolog with an optimizing native code compiler. Supposedly it's 5 to 10 times faster than commercial Prolog compilers or available interpreters.

[0] https://github.com/Mercury-Language/mercury

• lira

  1 21 0.0 Haskell

  Lira is a declarative domain-specific language designed to be the backbone of financial contracts that can be executed on the blockchain

  

Lira[0] and its readable paper[1] is a good example of abstracting smart contracts into a statically typed, domain-specific language that describes the contract precisely at a high level. It's not Turing complete, which works for a large class of contracts (for instance, see the American and Asian options examples in [1]).

One concern with logic programming is cost of computation, on Ethereum every transaction has a gas associated with it and so you can't run computations that go over the gas available in a block.

Turner's ideas of Total Functional Programming[2] might have application in the smart contract space as well, since you disallow general recursion but allow structural recursion, you can likely precalculate or bound gas costs accurately ahead of time.

As for being statically typed, I completely agree, Solidity's poor design choices contributed to millions of USD in loss (e.g. DAO hack) because the developers were not able to easily reason about the implicit behavior or concurrency model.

[0] https://github.com/etoroxlabs/lira

[1] https://bahr.io/pubs/files/bahr15icfp-paper.pdf

[2] http://www.jucs.org/jucs_10_7/total_functional_programming/j...

• Searching-In-An-Infinite-Space-Prolog

  1 1 0.0 Prolog

  PP2014 Prolog Homework

This brings up memories from 7 years ago. While in Uni, we had a homework: "Searching in an infinite space using Prolog".

Unfortunately, the comments are in my native language, but the assignment was to search for a box in an infinite space and bring it back to (0, 0).

It was fun: https://github.com/mateioprea/Searching-In-An-Infinite-Space...

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• clojure-graph-resources

  6 252 1.8

  A curated list of Clojure resources for dealing with graph-like data.

Probably worth mentioning for those interested in Datalog that there's actually a growing selection of databases for Clojure that use Datalog as their query language. I have documented them here: https://github.com/simongray/clojure-graph-resources#datalog

The Clojure variants of Datalog (they model triples as Clojure data structures) are basically becoming as ubiquitous in Clojure as SQL is elsewhere.

Suggest a related project