# Prolog

### Reification By Example

Reification is a tool in the bag of tricks that can be quite tricky to understand. Rather than waffle on in the abstract, let's take a look at a few examples.

### Opening the World with Three-Valued Logic

Under the open world assumption a fact can be True, False or Unknown. Prolog operates in a closed world where predicates are either True or False. Let's see if we can open Prolog up a little.

### Framing Frames

If you've been doing some reading, you may have come across the notion of frames as a data structure, but little available information on what they are and how they work. Implementations of frames are even rarer. In this post we'll examine what they are and consider alternative representations and implementations.

### The Golog Elevator

Golog is a logic programming language for dynamic domains based in Situation Calculus with an interpreter written in Prolog. The classic example from the book is that of an elevator. Here we present an interactive version of that program.

### Operators For A Controlled Natural Language

Prolog allows us to declare our own operators, this allows us to quickly take a bunch of predicates and query them in a bodge-job controlled "semi-natural" language.

### Reflexive, Symmetric and Transitive Relations in Prolog

When we start doing knowledge representation in Prolog, we start needing to describe the properties of relations so we can infer more than is in our recorded data. Symmetry, reflexivity and transitivity are the three main relationship properties you'll end up using. In this interactive post we take a look at how they can be encoded.

### Architecture Considerations for Prolog

Software architecture is a tricky subject at the best of times, often mitigated by following a framework. However, when you find yourself in the wilds of Prolog, there’s not much guidance out there, and not many templates to follow. In this post, I’ll provide some guidance built on the principal of substitution.

### Rock, Paper, Scissors, Prolog!

Simple, classic games like Rock, Paper, Scissors are good to code when learning a new language. The lovely thing about making this game in Prolog is you’re just encoding what it is, not how it is. It’s a subtle difference, but I’ll point it out during this explanation.

### Getting JSON data from an API in SWI-Prolog

Some folks don’t make their data available through RDF formats, or nice SPARQL endpoints, instead they provide a (REST/RESTFUL) API and will return JSON data for your request. It can be a little tricky figuring out how to get this data into your SWI-Prolog program. So in this post I demonstrate with a simple example.

### Setting Up Unit Testing In SWI-Prolog

Reading the docs for plunit, it can be quite tricky to figure out how to setup a nice unit testing environment and actually run those tests. In this post I demonstrate how I do it, keeping my tests separate from my code, and running them with a handy command.