A language shouldn't need to have a foundation in category theory in order to be "grounded in theory and informed by practice."

I think that Bob's (the OP's) is merely saying that the design of languages such as Rust and Swift has been strongly influenced by developers well-versed in type theory (the foundation of programming languages) as well as software development (the point of programming languages) -- this is true for Haskell as well, as he points out, but he is just noting that these well-designed, informed languages are becoming more mainstream.

Also, Rust's type system is more complex than you might expect, involving something called linear/affine types: http://en.wikipedia.org/wiki/Substructural_type_system#Linea...