Welcome to your first steps in Prolog! In this section, we will cover the basics to get you started with Prolog programming. By the end of this section, you should be able to write simple Prolog programs and understand how to run them.

• How to start the Prolog interpreter
• Writing and loading Prolog programs
• Basic Prolog queries

To begin using Prolog, you need to start the Prolog interpreter. Depending on your installation, you can start the interpreter by typing swipl (for SWI-Prolog) in your terminal or command prompt.

You should see a prompt like this:

This is the Prolog prompt where you can enter queries and commands.

Prolog programs consist of facts, rules, and queries. Let's start with a simple example.

Create a file named family.pl with the following content:

• Facts: These are basic assertions about the world. For example, parent(john, mary). states that John is a parent of Mary.
• Rules: These are logical statements that define relationships between facts. For example, grandparent(X, Y) :- parent(X, Z), parent(Z, Y). states that X is a grandparent of Y if X is a parent of Z and Z is a parent of Y.

To load your Prolog program, use the consult/1 predicate or the [filename] syntax at the Prolog prompt.

If the file is loaded successfully, you will see:

Now that your program is loaded, you can make queries to test it.

1. Who are the parents of Mary?

Output:

2. Who are the grandparents of Susan?

Output:

• The query parent(mary, Who). asks Prolog to find all individuals who are parents of Mary.
• The query grandparent(Who, susan). asks Prolog to find all individuals who are grandparents of Susan.

Add more facts to the family.pl file to include more family members and relationships. For example:

Define a new rule sibling/2 to determine if two individuals are siblings.

Query the sibling/2 rule to find siblings in the family.

1. Adding More Facts

2. Defining More Rules

3. Querying Siblings

• Syntax Errors: Ensure that each fact and rule ends with a period (.).
• Variable Names: Variable names in Prolog must start with an uppercase letter or an underscore (_).
• Consulting Files: Make sure the file path is correct when using the consult/1 predicate.

In this section, you learned how to start the Prolog interpreter, write simple Prolog programs, and make basic queries. You also practiced adding facts and rules to your program. In the next section, we will dive deeper into Prolog's syntax and structure. Keep practicing, and you'll become more comfortable with Prolog in no time!