Recover in Clojure

In Clojure, we can use the try and catch blocks to handle exceptions, which is similar to the concept of panic and recover in other languages. Here’s an example of how we can implement a similar functionality:

(ns recover-example
  (:require [clojure.core :refer [println]]))

;; This function throws an exception
(defn may-throw []
  (throw (Exception. "a problem")))

(defn main []
  (try
    (may-throw)
    ;; This code will not run because may-throw throws an exception
    (println "After may-throw")
    (catch Exception e
      ;; The catch block is similar to recover
      ;; It will catch the exception and allow the program to continue
      (println "Recovered. Error:\n" (.getMessage e)))))

;; Run the main function
(main)

In this example, we define a function may-throw that throws an exception, similar to the mayPanic function in the original example.

The main function uses a try-catch block to handle the exception. This is conceptually similar to using defer and recover in other languages. The try block contains the code that might throw an exception, and the catch block handles the exception if it occurs.

If an exception is thrown in the try block, the execution immediately jumps to the catch block. The code after may-throw in the try block will not be executed, similar to how the code after mayPanic() in the original example doesn’t run.

To run this program:

$ clj recover_example.clj
Recovered. Error:
 a problem

In Clojure, exceptions are used for error handling, which provides similar functionality to panic and recover in other languages. The try-catch mechanism allows you to catch exceptions and continue execution, preventing the program from crashing due to unexpected errors.

This approach is particularly useful in scenarios like server applications, where you wouldn’t want the entire server to crash if one client connection encounters an error. Instead, you can catch the exception, log it, close the problematic connection, and continue serving other clients.