Opt = object
  case kind*: OptKind
  of short:
      keyShort*: char

  of long:
      keyLong*: string

  of positional:
      nil

  value*: string
  error*: OptError

OptError {.pure.} = enum
  none, missing,            ## missing required value (when optValRequired) (after parsing all the args, last opt need value)
  extraneous                 ## extra value not needed (when optValNone)

OptKind {.pure.} = enum
  short,                    ## -s
  long,                     ## --long
  positional                 ## positional

OptValExpectation = enum
  optValRequired,           ## must have value
  optValNone,               ## must not have value
  optValOptional             ## value is optional
                             ## has : -k:v -k=v
                             ## has : -kv  (please don't rely on this behavior)
                             ## none: -k v

defaultOptSeparators = {'=', ':'}

posixOptSeparators = {'='}

proc `==`(a, b: Opt): bool {....raises: [], tags: [].}

iterator opts(argv: openArray[string];
              shortDefault: OptValExpectation = optValNone;
              longDefault: OptValExpectation = optValOptional;
              shortVal: openArray[(char, OptValExpectation)] = [];
              longVal: openArray[(string, OptValExpectation)] = [];
              sep: set[char] = defaultOptSeparators): Opt {....raises: [], tags: [].}