> For the complete documentation index, see [llms.txt](https://docs.otland.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.otland.net/lua-guide/concepts/iterators.md).

# Iterators

Iterators provide a way to traverse data. Iterators will usually use a closure to keep track of what data it's on and uses that to determine what to give next.

Take the iterator `ipairs` for example, it traverses a table in sequence. Its implementation can be written like this:

```lua
function ipairs(t)
    local index = 0
    return function()
       index = index + 1
       if t[index] then -- check if the value exists
           return index, t[index] -- key, value
       end
       return nil 
    end
end

local t = {1, 2, 3}
for k, v in ipairs(t) do
    print(k, v)
end
```

```
Output:
1 1
2 2
3 3
```

Using closures, you can define your own way to iterate through a set of data. You could iterate half of it forward and half of it backwards, iterate the entire thing in reverse, iterate every 2 values, etc.

Here's what a reverse `ipairs` would look like:

```lua
function revipairs(t)
    local index = #t + 1 -- start at the last index in the table, +1 to make sure it hits the end value when index-1 happens
    return function()
        index = index - 1 -- travel backwards from the end
        if t[index] then -- again, checking if the value exists
            return index, t[index]
        end
        return nil
    end
end

local t = {1, 2, 3}
for k, v in revipairs(t) do
    print(k, v)
end
```

```
Output:
3 3
2 2
1 1
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.otland.net/lua-guide/concepts/iterators.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.