itertools.nim

iterator imap[T,O](iter: iterator(): T {.closure.}, transform_elem: proc(e:T):O): O {.closure.} =
  var iterInst = iter
  for x in iterInst():
    yield transform_elem(x)

iterator ifilter[T](iter: iterator(): T {.closure.}, filter: proc(e:T):bool): T {.closure.} =
  var iterInst = iter
  for x in iterInst():
    if filter(x):
        yield x
        
proc ifold[T](iter: iterator(): T {.closure.}, f : proc(a:T, b:T):T, initval : T ):T  =
    var iterInst = iter
    result = initval
    for x in iterInst():
        result = f(result, x)

# usage:
# only works on closure iterators

iterator it(): int {.closure.} =
  for y in countup(1,10):
    yield y

echo "-----------"
for z in it.imap(proc(x:int):int = x*x):
  echo z
  
echo "-----------"
for z in it.ifilter(proc(x:int):bool = x > 4):
  echo z
  
echo "-----------"
echo it.ifold(proc(a,b:int):int = a+b, 0)