Is input validation a reasonable usecase for multimethods in Clojure?

Question

In the clojure.org documentation on multimethods it states:

Clojure multimethods ... can do validation of arguments and route to error-handling methods etc.

However, I don't see many examples of anyone using multimethods for this purpose. In the situation where I need to implement only a single method definition, does it still make sense to use multimethods to do input validation? For example:

(defmulti divide
          (fn [a b] (if (zero? b)
                      (throw (IllegalArgumentException. "Cannot divide by zero"))
                      :ok)))
(defmethod divide :ok [a b] (quot a b))

The advantage of this is that it keeps the final implementation of divide clean of input checking or error handling. Is there are more idiomatic way to get validation, error handling and clean syntax?

Answer 1

This is not what is meant by "route to error-handling methods". The technique being suggested is more like this:

(defmulti divide (fn [num denom] denom))
(defmethod divide 0 [num denon]
  (throw (IllegalArgumentException. "Cannot divide by zero")))
(defmethod divide :default [a b] (quot a b))

The error doesn't come from the dispatch function itself: rather, the dispatch function finds erroneous input values, and sends them to a dedicated error-handler, so that the other methods know they will always get valid input.