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kragenHNSource author
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I second the recommendation in Sir Whinesalot's post (which I haven't fully read yet) to look at …

I second the recommendation in Sir Whinesalot's post (which I haven't fully read yet) to look at miniKanren and microKanren. I found it extremely educational to port microKanren to OCaml a few years ago, and I think the result is somewhat more comprehensible than the original Scheme, though you'll still probably have to read the paper to understand it: http://canonical.org/~kragen/sw/dev3/mukanren.ml The most astonishing result of miniKanren is a Scheme interpreter that you can run forwards, backwards, or both. http://webyrd.net/quines/quines.pdf demonstrates using it to generate a Scheme quine, that is, a Scheme program whose output when run is itself ("miniKanren, Live and Untagged: Quine Generation via Relational Interpreters (Programming Pearl)", Byrd, Holk, and Friedman). §4.4 of SICP http://sarabander.github.io/sicp/html/4_002e4.xhtml also has an implementation of logic programming in Scheme which is extremely approachable. Unlike the post, I don't think Datalog is the place to look for deep insights about logic programming. …

Original discussionImplementing Logic Programming76 source comments · at import
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fcatalanHN

I concur that SICP 4.4 is very approachable. I once took a class that had a simple Prolog assignment, I recall we were given some building plans and had to program a path solver through the building. I thought it was a bit too easy and I wanted to dig deeper, because just doing the task left you with a taste of "this is magic, just use these spells". I looked at how to implement Prolog and was stumped until I found that SICP section. So I ported it to JavaScript and gave it a Prolog-like syntax and made a web page where you could run the assignment but also exposed the inner workings, and it was one of the neatest things I've ever handed in as coursework.

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sirwhinesalotHN

Insights shminsights, the database connection is where it is at :P (Thank you for reading the article, I also implemented microKanren before and it's insane how little code it takes to get full a logic programming engine going)

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anthkHN

Among SICP, https://t3x.org/amk/index.html Same approach. I think an older version of the book it's freely available, or maybe the one on Scheme itself. Scheme being homoiconic makes far easier to create quines.

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