(Please correct me if I'm wrong) but the NixOS functional language is also lazy. Guix does not have this lazy feature. Though on the other hand, it does play well with the rest of GNU.
Lazy evaluation in Scheme is achieved via delay/force macros, as well as simply quoting expressions to be evaluated later, perhaps by sending the quoted expression from the Guix client to the daemon.
Oh right, interesting. Now generally speaking I'd suspect things like concurrency, lazy and non-determinism should be made explicit in a language, these concepts should be language level not library/macro level. I'm quite curious to see how much this affects the expressiveness of the system. But I'm splitting hairs! This is LISP the old granddad of succinctness.