Conversely, a lot of people have have used dynamic typing in languages like JavaScript and Ruby. Their OO nature encourages creation of many types, while pervas

Conversely, a lot of people have have used dynamic typing in languages like JavaScript and Ruby. Their OO nature encourages creation of many types, while pervasive mutability removes any possibility to do local reasoning about the code. The situation is completely different in functional dynamic languages backed by immutable data structures.