The basic form of a HANDLER-CASE

condition-handler.lisp

;;;;  Condition Handler
;;;; The macro HANDLER-CASE establishes this kind of condition handler.

;;;; The basic form of a HANDLER-CASE is as follows:
;;;; (handler-case expression
;;;;   error-clause*)

;;;; where each error-clause is of the following form:
;;;; (condition-type ([var]) code)

(defun my-division (x y)
  (handler-case
      ;; The body of a HANDLER-CASE must be a single expression; you
      ;; can use PROGN to combine several expressions into a single form
      
      ;; Run this code
      ;; It is like try in (Python, Java and C++)
      (/ x y)
    
    ;; Condition type
    ;; It will cath any type of condition
    (error ()
      ;; It is like except in Python
      ;; It is like catch in Java or C++
      ;; Execute this code when there is an condition
      (format t "Something went wrong."))))

(defun my-division-v2 (x y)
  (handler-case
      ;; The body of a HANDLER-CASE must be a single expression; you
      ;; can use PROGN to combine several expressions into a single form
      
      ;; Run this code
      (/ x y)
    
    ;; Condition type
    ;; Execute this code when there is a condition equal to 'division-by-zero
    (division-by-zero ()
      (format t "You can't divide by zero!" ))))

(defun my-division-v3 (x y)
  (handler-case
      ;; The body of a HANDLER-CASE must be a single expression; you
      ;; can use PROGN to combine several expressions into a single form

      ;; Execute this code
      (/ x y)
    ;; Condition type
    ;; Execute this code when there is a condition equal to 'division-by-zero
    ;; The condition is signaled
    (division-by-zero ()
      (format t "You can't divide by zero!" ))
    
    ;; Condition type
    ;; Execute this code when there is a condition equal to 'type-error
    (type-error ()
      (format t "Both of them must be numbers!" ))))