[namanbharadwaj]

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...

[innguest]

I'd find it hard to justify nowadays understanding that there's a lot useful in Type theory but then ignoring Category theory. Even Object Orientation can be related to CT as coalgebras.

The type system in Haskell is not complex and that's a reason to like it. Everything derives from 6 simple rules:

http://en.wikipedia.org/wiki/Hindley%E2%80%93Milner_type_sys...

Simplicity in a type system makes it very expressive - contrast with complex, concrete type systems which do not allow e.g. Church numerals or linked lists to be represented within it.