I thought Elm was very much about web development. And Elixir is too in some ways. Both Scala and F# have a lot going on in the data space. Scala more so than F#. Standard ML is exciting because it's not big. And probably a better choice for understanding the fundamentals but Scala or F3 for something serious? This is just my best guess. Actually that reminds me of a very nice course in Standard ML from the University of Washington on Coursera, but it's not a book.