Conventions, Style, and Usage for Clojure Constants?

Question

What are the best practices for defining constants in Clojure in terms of style, conventions, efficiency, etc.

Answer 1

In Common Lisp, there's a convention of naming constants with plus signs (+my-constant+), and in Scheme, by prefixing with a dollar sign ($my-constant); see this page. Any such convention conflicts with the official Clojure coding standards, linked in other answers, but maybe it would be reasonable to want to distinguish regular vars from those defined with the :const attribute.

I think there's an advantage to giving non-function variables of any kind some sort of distinguishing feature. Suppose that aside from variables defined to hold functions, you typically only use local names defined by function parameters, let, etc. If you nevertheless occasionally define a non-function variable using def, then when its name appears in a function definition in the same file, it looks to the eye like a local variable. If the function is complex, you may spend several seconds looking for the name definition within the function. Adding a distinguishing feature like earmuffs or plus signs or all uppercase, as appropriate to the variable's use, makes it obvious that the variable's definition is somewhere else.

In addition, there are good reasons to give special constants like pi a special name, so no one has to wonder whether pi means, say, "print-index", or the i-th pizza, or "preserved interface". Of course I think those variables should have more informative names, but lots of people use cryptic, short variable names, and I end up reading their code. I shouldn't have to wonder whether pi means pi, so something like PI might make sense. None would think that's a run of the mill variable in Clojure.