Assert combinators are composable, light, terse (very little verbosity), types can be defined in single place, instead of type/interface definition you can use return type of assert function.

They don’t go into deep category theory, you won’t find monads and friends, they are first level, straightforward any typescript developer can pick up in minutes - this is by design. It stops at combinators in typescript to solve very specific problem and nothing more. Haskell in ts is not the goal of this npm.