[dgreensp]

There's nothing inherently slow or problematic about composing code out of "pure functions." The implication that evaluating functions requires doing lambda calculus, which requires a weird runtime like Haskell, is pure FUD. Haskell is weird for other reasons, like the fact that expressions are lazily instead of eagerly evaluated. You can compose your code out of pure functions in most any programming language.

Even when we're talking about facilities provided by the runtime, the fact that a programming language feature may have complex performance characteristics, in exchange for allowing the programmer to think about the problem in a more abstracted way, does not invalidate the abstraction. We might as well have an article about garbage collection called, "There is no garbage," making the point that at a lower level, all memory needs to be explicitly de-allocated. Or one called, "There is no immutability," pointing out that immutable data structures can only try to cover up the fundamental nature of computers, which have mutable memory cells.