Control Flow in Lisp: Conditionals and Loops

May 22, 2024

lisp

Welcome back to our ongoing journey of learning Lisp! In this post, we will delve into the fascinating world of control flow in Lisp, focusing on conditionals and loops. By the end of this post, you will have a solid understanding of how to navigate decision-making processes and create iterative operations within your Lisp programs.

Conditionals in Lisp

Conditionals in Lisp allow us to make decisions in our code based on certain conditions. The primary conditional construct in Lisp is the if statement. The basic syntax of an if statement is as follows:

(if <condition> <true-branch> <false-branch>)

Here’s an example to illustrate the usage of an if statement:

(defun check-temperature (temp)
  (if (<= temp 0)
      (format t "It's freezing outside!"
      (format t "It's a beautiful day!")))

In this example, if the temperature is less than or equal to 0, the message ‘It’s freezing outside!’ will be printed; otherwise, ‘It’s a beautiful day!’ will be printed.

Loops in Lisp

Loops in Lisp allow us to perform repetitive tasks or iterate over a sequence of elements. The primary loop construct in Lisp is the loop statement. The basic syntax of a loop statement is as follows:

(loop <loop-clauses> <body>)

Here’s an example to demonstrate the usage of a loop statement:

(defun print-numbers ()
  (loop for i from 1 to 5 do
    (format t "~a " i)))

In this example, the function print-numbers uses a loop statement to print numbers from 1 to 5.

By mastering conditionals and loops in Lisp, you gain the ability to control the flow of your programs and create dynamic and efficient code. Practice writing code using conditionals and loops to solidify your understanding of these essential concepts. Stay tuned for more Lisp tutorials and happy coding!