Some kinds of static type systems (by which I mean all of the widespread ones which aren't Haskell or similar to Haskell) make extremely specific guarantees sta

Some kinds of static type systems (by which I mean all of the widespread ones which aren't Haskell or similar to Haskell) make extremely specific guarantees static, such that you can't change mere implementation details without rewriting a lot of code. For example, if you're using a library which specifies floats as an input type, and you now need doubles, you're pretty well screwed: You either rewrite and recompile a huge chunk of code or you decide you don't need to expand your precision after all. Does the library code really need to use 16-bit floating-point values, or does it only use them because someone twenty years ago believed in some superstitions about performance? That information isn't available. It isn't in the type system, so it can only be in the documentation... oh, wait, documentation focuses on How and not Why, doesn't it? Your static type system was made by people who failed to disambiguate between storage size specifications and semantics, so you're left with "16-bit IEEE floating point" as the only semantic information you're ever going to have.