This is the 5th post in the Learning Clojure focus series. While describing how to cope with dynamic typing, we used the spec library. The library is not a true replacement for types - checks are executed at runtime instead of compile-time. On the flip side, it can go further than mere types, including emulating dependent types and programming-by-contract.

This week, I’d like to tackle an interesting approach that is quite useful. Design by contract prescribes that developers should define preconditions, postconditions and invariants. These specifications are referred to as 'contracts'.