IMO the sentence is incorrect. Static type systems would "enforce the stronger constraint" at run time... same as the dynamic type system. Perhaps the dynamic type system can have a fancy linter that does something crazy like running your code... but I'm not aware of any such linter.
Most static type systems that can do what clojure.spec can do tend to include runtime assertion and type checks and do not erase type data from runtime (what some static type zealots call "uni-type" approach).
For example Ada's type system, which has equivalent of Common Lisp's SATISFIES construct, which implements a runtime type assert that can use all the power of the language.
>Most static type systems that can do what clojure.spec can do tend to include runtime assertion and type checks and do not erase type data from runtime (what some static type zealots call "uni-type" approach).
When you don't erase the type data... you're gonna have more than one type. How is this a "uni-type" approach?
A popular (stupid) talking point in the stupid discussions about static/dynamic while missing that the axes were orthogonal, was for proponents of static types to claim that dynamic languages were "unityped" based on some convoluted logic about tagging data at runtime.
As someone who prefers static types, I agree with you that claiming dynamic languages are "unityped" is stupid. Javascript/Python/Clojure all literally have types.
> Perhaps the dynamic type system can have a fancy linter that does something crazy like running your code... but I'm not aware of any such linter.
Names in Clojure codebases and libraries are pretty reliably annotated with trailing exclamation marks, looking like: `save!`.
To that end, running Clojure code blindly to test it and its types is a fairly practical practice, coming up in cases like Ghostwheel [1], which uses this for generative testing of clojure.spec types, which can be much more sophisticated than what is commonly used in static systems, even with refinement types.
>which can be much more sophisticated than what is commonly used in static systems, even with refinement types
Can you elaborate on this? I have some experience with Clojure, and have been relatively unimpressed with spec. Everything it does I can do with (refinement) types (I think). Reading over the Spec documentation it constantly talks about predicates... which is exactly what a refinement type is.
