refined

> Compiling does not prove correctness for any program inputs. It can. For example in Scala there are libraries that allow you to define types for inputs e.g. this Int must be non-negative or this String must be greater than 5 characters. https://github.com/fthomas/refined

> I believe this sort of thing has a name, […] https://en.wikipedia.org/wiki/Refinement_type But the concept is just a little bit over 30 years old. So don't expect it shows up in most mainstream languages before the end of the next 20 years, and don't expect it to come to the C languages ever. Meanwhile in mainstream ML-land: https://github.com/Iltotore/iron (Or for the older version of the language: https://github.com/fthomas/refined) (Please also note that for this feature both versions don't need language support at all but are "just" libraries, as the language is powerful enough to express all kinds of type level / compile time computations in general.)

You're looking for refinement-types? Scala to the rescue: https://github.com/fthomas/refined And a new one: https://github.com/Iltotore/iron/ The latter will be zero overhead once a compiler ticket is closed. Both solutions will yield compile time checks where possible, and fall back to runtime checks when the data isn't statically known.

What forces you to use validator function and not just do Email(input)? This is how you actually do it in Scala if anyone interested https://github.com/fthomas/refined

I like for example Refined https://github.com/fthomas/refined not only for the static checking, scala> val i: Int Refined Positive = -5 <console>:22: error: Predicate failed: (-5 > 0). val i: Int Refined Positive = -5 but the expressive descriptions of a domain model.

I agree that most application-level code doesn't need new macros (you rarely have to develop a new macro to add a feature to an application) but there are definitely a lot of very legitimate use-cases for them outside of Shapeless. To give just a few: * https://github.com/adamw/macwire * https://github.com/fthomas/refined * https://github.com/adamw/quicklens * https://github.com/scala/scala-async * https://github.com/typelevel/machinist Even for cases where inductive implicits can do the job, there is still a bit of a push to prototype with shapeless and then rewrite with direct derivations of your instances later on to improve compile times. See e.g. https://github.com/circe/circe-derivation.