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

just use or:

(or input-argument "default")