"predicate-based data flow" is something I haven't heard before, what do you have in mind? I agree that clojure.spec2 can probably generate UI ... This gist is where Hyperfiddle DSL is roughly at right now but I think the Datomic schema definitions can be replaced by specs and the pull queries by s/select https://gist.github.com/dustingetz/96c928f755c736d2b525bb61a...

Spec has it's place, but I think people are trying to shovel spec in all sort of places; for example, heavy data parsing, making code very hard to track. Reminds me on core.logic movement couple of years ago, where everyone tried to have own parser/ui/whatever written in it, resulting very unreadable code.

What I'm really missing from spec is ability to disable it with flag or property, like "assert" macro. Sometimes I just want piece of code to run as fast as possible with less bytecode and instructions executed.

Isn't spec just a way to bolt on types to a dynamic language? And if you look at this way, can one have its cake and eat it too?

Thinking about Spec like a type-system is really not the right way to think. Its more dynamic validation system that works like regex for data-structures.

unless you think about types the way Haskell does.

Code readability is massively underrated.