SWAG[T] = ref object
  op: proc (x, y: T): T
  e: T
  top: seq[T]
  bottom: seq[T]
  topfold: seq[T]
  bottomfold: seq[T]

CPLIB_COLLECTIONS_SWAG = 1

proc `$`[T](self: SWAG[T]): string

proc `[]`[T](self: SWAG[T]; index: int): T

proc addFirst[T](self: SWAG[T]; x: T)

proc addLast[T](self: SWAG[T]; x: T)

proc fold[T](self: SWAG[T]): T

proc initSWAG[T](op: proc (x, y: T): T; e: T): SWAG[T]

proc len[T](self: SWAG[T]): int

proc popFirst[T](self: SWAG[T]): T

proc popLast[T](self: SWAG[T]): T