In addition to the sibling comments: worth noting that spec offers you a-la-carte typing - typing when/where/how you please. This is very different from the exp

In addition to the sibling comments: worth noting that spec offers you a-la-carte typing - typing when/where/how you please. This is very different from the experience of having to constantly satisfy a compiler. Generally I decide to 'spec' a tiny percent of my code - just the most critical one, or APIs with complex method signatures, etc. When doing so, if the spec'd function used N other functions, one could argue that those N functions are also being implicitly checked.