In Clojure how to choose a value if nil

Question

In Clojure what is the idiomatic way to test for nil and if something is nil then to substitute a value?

For example I do this a lot:

 let [ val    (if input-argument input-argument "use default argument")]

: but I find it repetitive having to use "input-argument" twice.

Answer 1

Alex's suggestion of "or" is indeed the idiomatic way to rewrite your example code, but note that it will not only replace nil values, but also those which are false.

If you want to keep the value false but discard nil, you need:

(let [val (if (nil? input-argument) "use default argument" input-argument)]
   ...)