itertest.nim

type filterProc[T] = proc (value:T): bool {.closure.}

iterator dropWhile* [iT, rT](predicate: filterProc[rT], iter: iT): rT =
  ## An iterator that drops (skips) elements from the iterable as long as the
  ## predicate is true; afterwards, returns every element. 
  ## Note, this version of the iterator does not produce any output until
  ## the predicate first becomes false, so it may have a lengthy start-up time.
  var 
    broken = false
    element: rT
  while not finished(iter):
    element = iter() # This will only work with iterables that take no args.
    if not broken and not predicate(element):
      broken = false
      yield element

when isMainModule:
  block:
    iterator testIter: int = 
      for i in 0..10:
        yield i

    proc predProc(element: int): bool =
      result = (element == 5)

    var
      dwResult = @[5,6,7,8,9,10]
    var dwOutput = newSeq[int]()
    for i in dropWhile[type(testIter), int](predProc, testIter):
      dwOutput.add(i)
    assert(dwOutput == dwResult)