> The beauty of FP is that from your code's point of view there is no mutation. The beauty of pure FP is that from your code's point of view there is no mutati

> The beauty of FP is that from your code's point of view there is no mutation. The beauty of pure FP is that from your code's point of view there is no mutation. The only functional language you mentioned in your post is OCaml, which is impure and supports ad-hoc mutation, like every other language in the ML family, and like every other functional language except for a select few like Haskell and Miranda and their derivatives. Moreover Haskell supports other kinds of mutation besides fusion and tail-call elimination; it just does it behind a pure interface. See, for example, http://hackage.haskell.org/package/array-0.1.0.0/docs/Data-Array-IO.html http://hackage.haskell.org/package/array-0.1.0.0/docs/Data-A... . So we're back at the same place: obviously mutation is useful since even Haskell goes out of its way to make sure you have access to it.