I agree that while Julia has a lot of functional programming elements, it's not strictly a functional programming language. It also is built for things where heap-allocated arrays are necessary: you're not going to be scientific computing with 100GB stack-allocated arrays. Having the base arrays be stack-allocated and then having StaticArrays for stack-allocated arrays works well, though that means you do want to use imperative styles a lot when managing the large array operations to cut down on allocations. Spiral and Julia are just very different and cater to different paradigms and applications.