4.0 Advanced Programming Techniques

Logo provides structures for creating more sophisticated and reusable code.

4.1 Procedures

Procedures (also known as subprograms or functions) allow a collection of commands to be encapsulated and given a name.

• Definition: A procedure begins with the keyword to followed by the procedure name, and concludes with the keyword end. The Edall button or command opens a text editor for defining procedures.
• Execution: Once defined, a procedure can be run by typing its name in the command line (e.g., square).
• Arguments: Procedures can accept input values, or arguments, making them more versatile. An argument is declared with a colon in the definition line (e.g., to square :n). When the procedure is called, a value for the argument is provided (e.g., square 50).

4.2 Recursive Procedures

A recursive procedure is one that includes a call to itself within its own definition. This technique is powerful for solving problems that can be broken down into smaller, self-similar sub-problems. A recursive procedure must have a “stop” condition to prevent it from running indefinitely.

Example from source:

to spiral_recur :n

if :n < 1 [stop]

fd :n

rt 20

spiral_recur 0.95 * :n

end

4.3 Randomization

The random command introduces unpredictability into programs. It takes a single integer argument and returns a randomly chosen integer between 0 and one less than the argument’s value. For example, random 360 will produce a value from 0 to 359.