macro.md

A little Clojure challenge inspired by Let over Lambda.

Write a macro (you can try a function, but it's impossible) that accepts four arguments:

1. an expression that returns a number
2. something to return if that number's negative
3. something to return if that number's zero
4. something to return if that number's positive

Here's the signature: (defmacro nif [expr neg zero pos] ...)

To pass my test, the following form should print "pos!" and return "pos.", with no other side effects:

(nif 10
      (do (println "Negative!") "negative.")
      (do (Thread/sleep 1000000) "zero.")
      (do (println "pos!") "pos."))

May the best lisper win!

:else is just a convention, since keywords are always truthy. This is equally valid, but unclear:

(cond (pos? x) "pos"
      (neg? x) "neg"
      "FALSE!" "zero")