-module(prog).
-export([main/0]).

main() ->
  return_positions([a, b, c]).

return_positions(X) ->
  return_positions(X, [], 1).
return_positions([], Out, _I) ->
  lists:reverse(Out);
return_positions([Head | Tail], Out, I) ->
  return_positions(Tail, [{Head, I}] ++ Out, I + 1).