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My Common Lisp Practice

Uncommon People like it

References

<Note>

  • Use GNU CLISP 2.49.93 - GNU 9.1.0 in JDoodle, unless otherwise specified

<List>

Fibonacci Sequence (2024.12.15)

  • Generate the Fibonacci sequence using both regular recursive and tail-recursive methods

  • Common Lisp features a variety of functions with similar purposes, such as if and cond, loop and dotimes.

  • While it may look similar to Clojure at first glance, Clojure is a Lisp-1 while Common Lisp is a Lisp-2, making them somewhat different.

  • Code and Output

    Code : FibonacciSequence.lisp 
    ;; Regular recursive Fibonacci function
(defun fib-recursive (n)
  "Calculate the n-th Fibonacci number using regular recursion."
  (cond ((= n 1) 1)                             ; cond means "condition" and is used like if-else if or switch statements in other languages.
        ((= n 2) 1)
        (t (+ (fib-recursive (- n 1))           ; t means "true" and is always evaluated as true. It is used as the default-consequent in cond.
              (fib-recursive (- n 2))))))

;; Tail-recursive Fibonacci function
(defun fib-tail-recursive (n &optional (a 1) (b 1))
  "Calculate the n-th Fibonacci number using tail recursion."
  (if (<= n 1)
      a                                         ; then-expression: executed if the condition is true.
      (fib-tail-recursive (1- n) b (+ a b))))   ; optional-else-expression: executed if the condition is false (no explicit 'else' keyword is required).

;; Function to calculate and print Fibonacci numbers
(defun print-fibonacci-numbers (n)
  "Calculate and print Fibonacci numbers up to the n-th term."
  (format t "Fibonacci sequence up to the ~Dth term~%" n)
  (format t "Regular recursive method : ")
  (dotimes (i n)                                ; dotimes is similar to loop but is simpler and specifically used for iterating a fixed number of times.
    (format t "~D " (fib-recursive (1+ i))))
  (format t "~%Tail recursive method    : ")
  (dotimes (i n)
    (format t "~D " (fib-tail-recursive (1+ i)))))
    ;; Example execution
(print-fibonacci-numbers 10)
    Output 
    Fibonacci sequence up to the 10th term
Regular recursive method : 1 1 2 3 5 8 13 21 34 55 
Tail recursive method    : 1 1 2 3 5 8 13 21 34 55