Comment by lbj

The overall conclusion is correct, most error messages happen by accident, but a lot the examples look like expected behavior to me. Maybe because Ive been using Clojure for too long, or maybe because its the expected trade-off when using a dynamically typed language. You get more fluidity at the cost of type checks - The way to mitigate this downside is adding checks of your own. Clojure has supported this since way back when using pre/post conditions.

Example:

  core> (defn mydiv [n d] {:pre [(pos? d)]} (/ n d))
  #'mydiv
  core> (mydiv 10 2)
  5
  core> (mydiv 10 0)
  AssertionError Assert failed: (pos? d)  core/mydiv

As opposed to the standard

  core> (/ 10 0)
  ArithmeticException Divide by zero    
  clojure.lang.Numbers.divide (Numbers.java:158)

Chasing down Numbers.java will take time, but with a pre-condition you get the exact name of the function and the test which failed.