Comma quibbling is a task originally set by Eric Lippert in his blog.



Task

Write a function to generate a string output which is the concatenation of input words from a list/sequence where:

 An input of no words produces the output string of just the two brace characters "{}".
 An input of just one word, e.g. ["ABC"], produces the output string of the word inside the two braces, e.g. "{ABC}".
 An input of two words, e.g. ["ABC", "DEF"], produces the output string of the two words inside the two braces with the words separated by the string " and ", e.g. "{ABC and DEF}".
 An input of three or more words, e.g. ["ABC", "DEF", "G", "H"], produces the output string of all but the last word separated by ", " with the last word separated by " and " and all within braces; e.g. "{ABC, DEF, G and H}".


Test your function with the following series of inputs showing your output here on this page:

 [] # (No input words).
 ["ABC"]
 ["ABC", "DEF"]
 ["ABC", "DEF", "G", "H"]


Note: Assume words are non-empty strings of uppercase characters for this task.




defmodule RC do
  def generate( list ), do: "{#{ generate_content(list) }}"
 
  defp generate_content( [] ), do: ""
  defp generate_content( [x] ), do: x
  defp generate_content( [x1, x2] ), do: "#{x1} and #{x2}"
  defp generate_content( xs ) do
    [last, second_to_last | t] = Enum.reverse( xs )
    with_commas = for x <- t, do: x <> ","
    Enum.join(Enum.reverse([last, "and", second_to_last | with_commas]), " ")
  end
end
 
Enum.each([[], ["ABC"], ["ABC", "DEF"], ["ABC", "DEF", "G", "H"]], fn list ->
  IO.inspect RC.generate(list)
end)