Question

So I have defined say a keyword:

(def a :hello)

how do I check that it implements the IFn interface?

Answer 1

For the general case, you can use the instance? predicate:

(instance? <class-or-interface> <object>)

Quoting the documentation:

(instance? c x) evaluates x and tests if it is an instance of the class
c. Returns true or false.

For example:

(instance? java.lang.String "test")
> true

(instance? java.io.Serializable "test")
> true

For the code in the question, do something like this:

(instance? package.of.IFn a)

Or, as has been pointed out in the comments, for the very specific case of asking if a is an instance of IFn this will work:

(ifn? a)