Adding RangeExtras.new(first, last, step)

[h4cc]

How about adding new(first, last, step), which is not covered by Elixirs Range.new by default?

I see this may not work with the other functions, but this is the only "range" library i could find on hex so far.

[h4cc]

This was the initial issue: elixir-lang/elixir#1039

[h4cc]

Here some code working for ascending stepped ranges:

  @doc """
  Will create a ascending range from first to last using delta as step size.

  iex> MyRange.steps(1, 1, 2)
  [1]

  iex> MyRange.steps(1, 2, 2)
  [1]

  iex> MyRange.steps(1, 3, 2)
  [1, 3]

  iex> MyRange.steps(1, 4, 2)
  [1, 3]

  iex> MyRange.steps(1, 5, 2)
  [1, 3, 5]

  iex> MyRange.steps(1, 10, 3)
  [1, 4, 7, 10]
  """
  # Catch invalid arguments.
  def steps(first, last, _) when (last < first), do: raise "`last` has to be higher than `first`"
  def steps(_, _, delta) when (delta < 1), do: raise "`delta` has to be a integer > 1"

  # Fallback to old range
  def steps(first, last, 1), do: Range.new(first, last)

  # Implementation for ascending range.
  def steps(first, last, delta) when (last >= first) and (delta > 1) do
    first
    |> Stream.iterate(&(&1+delta))
    |> Enum.take_while(&(&1 <= last))
  end

[lnikkila]

Looks good. I’m kind of swamped with other stuff right now but if you can find some time to make a PR with some test coverage (those doctests should work, maybe some tests for raise?) I’d be happy to merge that in! Also please indicate that you agree to license your contribution under the ISC license, see README.md. Thanks!