It kind of is, but pre/post-conditions can be more than that. Also, I'd consider it bad form to have type signatures (which they have) and runtime checking the

It kind of is, but pre/post-conditions can be more than that. Also, I'd consider it bad form to have type signatures (which they have) and runtime checking the same types. The whole point of having static typing is decreasing the need for the latter, but you have to actually run a type checker for it to be useful.