You can also use anonymous functions if you find the module syntax a little terse or clunky for shell scripting.

    double = fn a -> add.(a, a) end
    double.(4)

It starts to look a bit like a weird untyped OCaml / F# if you use pattern matching:

    f = fn
      x, y when x > 0 -> x + y
      x, y -> x * y
    end