The fact that I cannot, in the absence of perfect test coverage, verify the correctness of someone’s code is a big red flag. Pssst... you can't do this

The fact that I cannot, in the absence of perfect test coverage, verify the correctness of someone’s code is a big red flag. Pssst... you can't do this with any type system. You might be able to come close with some of the fancier dependent-typing stuff, but at some point a "sufficiently-specific type specification" starts looking an awful lot like a QuickCheck-style test.