Szathmáry László honlapja @ DEIK | Nim2 / Finite and infinite iterators

An iterator can be finite or infinite. Let's see an example for each.

Finite iterator

iterator down(n: Positive): int =
## Iterate down to 0 (incl.).
var n: int = n
while n >= 0:
yield n
dec n

proc main() =
for n in down(3):
echo n

main()

Output:

Infinite iterator

An infinite iterator would never stop generating values. So you must pay attention on the caller side to stop the iteration (with a break, for instance).

iterator up(n: int): int =
## Iterate up from `n` (incl.).
var n = n
while true:
yield n
inc n

proc main() =
var cnt = 0
for n in up(10):
echo n
cnt += 1
if cnt >= 5:
break
#
#

main()

Output:

Here we print just the first five elements and then we stop.