I'd love to use all this but the fact that you have to substitute in variables just makes this very not-useful.

Ideally in functional programming everything is a (pure) function (and this is how I program), so you never have your variables defined.

Instead, my standard setup is to debug a function by saving its arguments in a vector, e.g.

  (defn buggy-function [a b c]
   (def test-bf [a b c]) ;; <- add this
   ... function body ...
  )

Then I can call buggy-function with

  (apply buggy-function test-bf)

and modify the code until it behaves as expected.

This is also where immutability has its grand appearance.