I wonder what makes them say this in the FAQ: "a flexible enough type system for concatenative languages has not yet been designed. However, Factor 2.0 may include optional static typing, if a suitable type system can be found." http://kittenlang.org/ gives the impression of having a fairly sensible static type system.
Hey, I’m the author of Kitten. The site & repo are a bit out of date, but I’m currently working on a release. Would be happy to answer any questions. :)
I think the problem is that you want some words with dynamic/value-dependent stack effects. It’s hard to intermingle static and dynamic typing well, and hard to bring the utility of dependent typing for enforcing program properties into the realm of properties that are actually useful to enforce while remaining usable.
