I think it's better referred to as a toolkit for building more correct software. One of the things it can be used for is to check variable types at dev time, j

I think it's better referred to as a toolkit for building more correct software. One of the things it can be used for is to check variable types at dev time, just as static type systems check a type compile time. It can also be used for runtime validation, randomized generative testing, more advanced checks/rules than current type systems can specify(eg checking outputs are correctly related to inputs). Also an important philosophical difference with type systems is an open approach to data structure, where types are generally closed. The concept is that it allows more flexible systems that are easier to adapt to new needs. Here's the best intro to spec I've seen, it's long and sound is terrible, but it's a great talk. https://vimeo.com/195711510 https://vimeo.com/195711510