Comment by slaymaker1907

Please write a type for the following function:

  def compose(start, *args):
    def helper(x):
      for func in reversed(args):
        x = func(x)
      return start(x)
    return helper

There is no mainstream typed language which can write a fully general type for the vararg compose function. TypeScript is probably the one that comes closest, but last I checked it still was unable to write a sufficiently powerful array type. You can write a type for a version of compose with a fixed number of arguments, but not for one working over an arbitrary number of arguments.