Elm has neat ideas, but there's really no need for an entirely new programming language just for functional reactive stuff, and I'm just not into languages that don't support dynamic and iterative development at the REPL. Hot swapping code is a poor replacement for a real REPL.
I think it's great to have more choices of purely functional, statically typed languages for web programming. The only other options I'm aware of are GHCjs and Haste (huge runtime size, incomprehensible code, laziness), and PureScript. PureScript to me seems like the ideal choice of the options available, with a more powerful type system and more of a general-purpose approach. But it doesn't have Elm's tooling, its nice error messages, or its wealth of FRP tutorials. Certainly, PureScript doesn't obviate Elm IMO.
"Before explaining how that program is written, let’s first make a small detour, and introduce the REPL (Read Eval Print Loop) tool, that Elm — like many other functional languages — provides. The elm repl command starts it, like so:"
I started learning and tinkering with Elm back in early October and was impressed (still am). However, I quickly found myself wishing for more flexible type-level abstractions; namely type classes[1], though I didn't realize it yet because I didn't have a Haskell background. Also, I was a little wary of dipping too much into ffi territory (which I sensed I would need to do for my use cases), since that aspect of the language is still in flux (at least, that was my impression).
In November, I started learning PureScript, and I've found PureScript by Example[2] to be an excellent resource. There are a few sections where I think the author moves a little too quickly, but I found that by spending time in psci (PureScript's REPL) I could usually fill in what, for me, were gaps in the explanations. The REPL has further proved invaluable in my fledgling development efforts with PureScript, and the language's ffi is straightforward.
