Iterators: Difference between revisions

</pre>

=={{header|Nim}}==

Nim defines iterators for collection types such as arrays, sequences, sets, tables, etc. But it allows also to define our own iterators. There exists two kinds of such iterators: inline iterators (the current default) and closure iterators. Inline iterators are expanded, closure iterators are not.

In our solution, we use standard iterators and our own iterators.

<syntaxhighlight lang="Nim">import std/lists

# Days stored in an array.

let days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]

# Colors stored in a doubly linked list.

let colors = ["Red", "Orange", "Yellow", "Green", "Blue", "Purple"].toDoublyLinkedList

### To print the elements of "days", we use a standard iterator.

echo "Content of “days” array:"

for day in days:

echo day

echo()

### To print the elements of "colors", we use a standard iterator.

echo "Content of “colors” list:"

for color in colors:

echo color

echo()

### To print the first, fourth an fifth elements

### of "days", we use a standard iterator.

echo "First, fourth and fifth elements of “days”:"

for i, day in days:

if i + 1 in [1, 4, 5]:

echo day

echo()

### To print the first, fourth an fifth elements

### of "colors", we must define our own iterator.

iterator enumerate[T](list: DoublyLinkedList[T]): (int, T) =

## Yield the successive (index, value).*

## First index is 0.

var i = 0

var node = list.head

while node != nil:

yield (i, node.value)

node = node.next

inc i

echo "First, fourth and fifth elements of “colors”:"

for i, color in colors.enumerate:

if i + 1 in [1, 4, 5]:

echo color

echo()

### To print the last, fourth to last, and fifth to last

### elements of "days", we must define our own iterator.

iterator revItems[T](a: openArray[T]): (int, T) =

## Starting from end of array, yield (index, value).

## First index is 1.

for i in countdown(a.high, 0):

yield (a.len - i, a[i])

echo "Last, fourth to last and fifth to last elements of “days”:"

for i, day in days.revItems:

if i in [1, 4, 5]:

echo day

echo()

### To print the last, fourth to last, and fifth to last

### elements of "colors", we must define our own iterator.

iterator revItems[T](list: DoublyLinkedList[T]): (int, T) =

## Starting from end of the list, yield (index, value).

## First index is 1.

var i = 1

var node = list.tail

while node != nil:

yield (i, node.value)

node = node.prev

inc i

echo "Last, fourth to last and fifth to last elements of “colors”:"

for i, color in colors.revItems:

if i in [1, 4, 5]:

echo color

</syntaxhighlight>

{{out}}

<pre>Content of “days” array:

Sunday

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

Content of “colors” list:

Red

Orange

Yellow

Green

Blue

Purple

First, fourth and fifth elements of “days”:

Sunday

Wednesday

Thursday

First, fourth and fifth elements of “colors”:

Red

Green

Blue

Last, fourth to last and fifth to last elements of “days”:

Saturday

Wednesday

Tuesday

Last, fourth to last and fifth to last elements of “colors”:

Purple

Yellow

Orange