Nurikabe solver

[Mark Engelberg]

For fun, and to learn Picat, I programmed a Nurikabe solver.

https://github.com/Engelberg/PicatProjects/blob/main/nurikabe.pi

https://en.wikipedia.org/wiki/Nurikabe_(puzzle)

To be completely honest, I found the development experience to be a struggle, in the sense that the editor wasn't great, the interactive terminal not terribly useful, the error messages rarely helpful, and not a lot of tools for working out what was going wrong. I spent a lot of time commenting out various sections of code to try to isolate errors, since I couldn't find a better methodology for debugging. However, I am deeply impressed with the elegance and concision of the final code, and the speed of execution.

It solved in under 1 second a puzzle that took about 5 minutes using a comparable model on the SAT solver I usually use (SAT4J using an interface I wrote from Clojure), and to do it in SAT4J I had to implement my own binary numeric representations and addition in order to write a connected component constraint, which you get "for free" in Picat.

Thanks to Hakan for getting me unstuck with my rookie bugs.

This was just for fun, so I don't really need to improve this program further, but I'm always interested in learning how to use a language idiomatically, so comments are certainly welcome.

[Neng-Fa Zhou]

Thank you for your feedback. Picat is still a young language, and a lot of work needs to be done in order to make it more user friendly. Syntax error messages should be more informative, and runtime error messages should be issued with a stack trace. It is always a challenge to debug an unsatisfiable model in constraint programming. I, like many other people, often comment out some constraints in order to locate the constraint that makes a model unsatisfiable. This error-and-trial process is often time consuming.

Cheers,

Neng-Fa

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