Holy-Elie Scaide

A day with Prolog

My first programming languages was C, which is part of the Fortran family. Lately, I've been learning fundamentally different languages, starting with Lisp and the more modern Clojure. I've taken a brief look at Forth. The latest I've tried is Prolog. And it was by far the most enlightening experience I had.

Prolog is a logic programming language, allowing you to express facts and rules about a given domain. Facts are rules or relations that you hold as true. Rules can contain other rules and itself. It is true if all the sub-rules are true. A query is a fact evaluated by the interpreter, either verifying if it's true or what values will make it true.

Expressing a program in terms of relations instead of statements is great for prototyping. Rather than finding a computation procedure, you're describing all the known facts of the problem, then its constraints. A Prolog algorithm is more a specification than a procedure. The only pain point for me now is the difficulty of dealing with side effects, mainly IO.


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