Question

I´ve been struggling with finding a proper way to do error handling in Clojure, and like some thoughts on the subject.

Given an example with no error handling:

(defn do-stuff
   (let [result1 (some-function) 
         result2 (other-function)
         result3 (yet-another-function)]
   {:status 200
    :body (foo result1 result2 result3)}))

If there is an error somewhere, the following should be returned:

 {:status 4xx
  :body "Some descriptive error message, based on what went wrong"}

How to make sure that result1-3 are valid before they are passed to foo?

In case something goes wrong inside one of the functions in the let block (assuming there is no proper way to handle an error inside these functions), should they throw an exception to be handled in do-stuff?

Answer 1

If they throw Exceptions you can catch them outside the let:

(defn do-stuff
  (try
   (let [result1 (some-function) 
         result2 (other-function)
         result3 (yet-another-function)]
   {:status 200
    :body (foo result1 result2 result3)})
   (catch MyException e
     {:status 4xx
      :body (str "Some descriptive error message, " (.getMessage e)})