Clojure best practice for nested let

Question

Is is good practice to use Clojure nested let in the following way, or is it confusing ?

(defn a-fun [config]
  (let [config (-> config (parse) (supply-defaults))]
  ;; do something with config
  ))

I noticed I have this pattern of parsing/checking/validating things quite often in my input functions that talk to the external world (in this case a Clojurescript library that exposes public functions, but I also had Compojure routes with this same feeling).

Is it confusing, because one has to understand the rules for bindings visibility (not sure what the exact wording is) ?

What would be the idiomatic way to do it ? Change the config name to parsed-config, put it in another function, something else completely ?

Answer 1

I would reach for this idiom when

• the rebinding is the same kind of thing and
• you want to make clear that the local binding supersedes the global one.

For example

(defn fact [n]
  (loop [n n, answer 1]
    (if (pos? n)
      (recur (dec n) (* answer n))
      answer)))

This also stops you using the global binding by accident, as I was prone to do.