In this section, we will cover the fundamental syntax and structure of Prolog programs. Understanding these basics is crucial for writing and interpreting Prolog code effectively.

1. Atoms
2. Numbers
3. Variables
4. Complex Terms
5. Comments
6. Clauses
7. Programs

Atoms are the most basic type of data in Prolog. They are constants and can be:

• A sequence of letters, digits, and underscores starting with a lowercase letter (e.g., apple, x1, my_variable).
• A sequence of special characters (e.g., +, :-, -->).
• A string of characters enclosed in single quotes (e.g., 'Hello World', '123').

Prolog supports integers and floating-point numbers:

• Integers: 42, -7
• Floating-point numbers: 3.14, -0.001

Variables in Prolog start with an uppercase letter or an underscore. They are placeholders for terms:

• X, Y, Result
• _Temp, _

Complex terms (or structures) consist of a functor and a fixed number of arguments:

• functor(arg1, arg2, ..., argN)
• Example: point(3, 4), person(name, age)

Comments are used to annotate the code and are ignored by the Prolog interpreter:

• Single-line comments start with %.
• Multi-line comments are enclosed between /* and */.

Prolog programs are composed of clauses, which can be facts, rules, or queries:

• Facts: State something unconditionally true.

  likes(mary, pizza).
  

• Rules: State something conditionally true.

  likes(mary, X) :- food(X), italian(X).
  

• Queries: Ask whether something is true.

  ?- likes(mary, pizza).
  

A Prolog program is a collection of clauses. The order of clauses can affect the program's behavior due to Prolog's depth-first search strategy.

Define facts for the following:

1. john likes ice_cream.
2. susan likes chocolate.

Solution:

Define a rule that states john likes something if it is a dessert.

Solution:

Write a query to check if susan likes chocolate.

Solution:

• Case Sensitivity: Remember that Prolog is case-sensitive. apple and Apple are different.
• Variable Naming: Variables must start with an uppercase letter or an underscore.
• Quotes: Use single quotes for atoms that contain spaces or special characters.

In this section, we covered the basic syntax and structure of Prolog, including atoms, numbers, variables, complex terms, comments, clauses, and how to structure a Prolog program. Understanding these basics is essential for progressing to more advanced topics in Prolog programming. In the next section, we will delve into defining facts, which are the building blocks of Prolog programs.