> ## Documentation Index
> Fetch the complete documentation index at: https://docs-v1.latitude.so/llms.txt
> Use this file to discover all available pages before exploring further.

# Loops and Iteration

> Learn how to add multiple messages based on loop conditions in your prompts

## Overview

Loops in PromptL allow you to dynamically generate content or messages by iterating over lists or arrays. This is particularly useful for creating adaptive prompts based on user input or contextual data.

With loops, you can:

* Repeat sections of your prompt for each item in a list.
* Access each item's index for numbered output or additional logic.
* Handle empty lists gracefully using the `else` clause.

***

## Syntax

### Basic Loop

A loop is defined using the `for` and `endfor` keywords, wrapped in `{{ }}`. The content inside the loop is repeated for each item in the list.

```tsx theme={null}
{{ for item in list }}
  - {{ item }}
{{ endfor }}
```

### Loop with Index

You can include an `index` parameter to track the iteration count, starting from `0`.

```tsx theme={null}
{{ for item, index in list }}
  {{ index }}: {{ item }}
{{ endfor }}
```

### Loop with `else`

The `else` clause runs when the list is empty. Place it before the `endfor` keyword.

```tsx theme={null}
{{ for item in list }}
  - {{ item }}
{{ else }}
  No items to display.
{{ endfor }}
```

***

## Examples

### Basic Example: Listing Items

```tsx theme={null}
{{ for fruit in ["apple", "banana", "cherry"] }}
  - {{ fruit }}
{{ endfor }}
```

**Output**:

```
- apple
- banana
- cherry
```

### Example with Index

```tsx theme={null}
{{ for fruit, index in ["apple", "banana", "cherry"] }}
  {{ index + 1 }}. {{ fruit }}
{{ endfor }}
```

**Output**:

```
1. apple
2. banana
3. cherry
```

### Handling Empty Lists

```tsx theme={null}
{{ for item in [] }}
  - {{ item }}
{{ else }}
  The list is empty. No items to display.
{{ endfor }}
```

**Output**:

```
The list is empty. No items to display.
```

***

## Advanced Usage

### Iterating Over Objects

Loops can handle more complex data structures, such as arrays of objects.

```tsx theme={null}
{{ for user in users }}
  - Name: {{ user.name }}, Age: {{ user.age }}
{{ endfor }}
```

For the input:

```tsx theme={null}
users = [
  { name: "Alice", age: 30 },
  { name: "Bob", age: 25 }
]
```

**Output**:

```
- Name: Alice, Age: 30
- Name: Bob, Age: 25
```

***

### Nested Loops

You can use nested loops for iterating over multi-dimensional data.

```tsx theme={null}
{{ for group, groupIndex in groups }}
  Group {{ groupIndex + 1 }}:
  {{ for member in group.members }}
    - {{ member }}
  {{ endfor }}
{{ endfor }}
```

For the input:

```tsx theme={null}
groups = [
  { members: ["Alice", "Bob"] },
  { members: ["Charlie", "Dana"] }
]
```

**Output**:

```
Group 1:
  - Alice
  - Bob
Group 2:
  - Charlie
  - Dana
```

***

## Best Practices

1. **Keep Loops Simple**:
   * Avoid deeply nested loops unless necessary. Complex loops can make your prompts harder to read and maintain.
2. **Use Default Values**:
   * Provide defaults for variables to prevent errors when lists are empty or data is incomplete.
   * Example: `{{ item || "Unknown" }}`
3. **Combine with Conditionals**:
   * Use `if` statements inside loops for conditional logic.
   ```tsx theme={null}
   {{ for user in users }}
     {{ if user.active }}
       - {{ user.name }} (Active)
     {{ else }}
       - {{ user.name }} (Inactive)
     {{ endif }}
   {{ endfor }}
   ```
4. **Debugging**:
   * Temporarily output the list and its elements to ensure the loop is iterating as expected.

***

## Debugging Tips

If your loop isn’t working as expected:

* **Verify Data**: Print the list you’re iterating over to ensure it contains the expected data.
* **Check Syntax**: Ensure `endfor` is present and properly matched with `for`.
* **Use `else` for Debugging**: Add an `else` clause to confirm whether the list is empty.

```tsx theme={null}
{{ for item in list }}
  - {{ item }}
{{ else }}
  Debug: The list is empty or not defined.
{{ endfor }}
```

***

## Summary

Loops in PromptL enable you to iterate over lists dynamically, generate repeated content, and handle complex data structures. By combining loops with variables and conditionals, you can create powerful, adaptive prompts tailored to any use case.

> Ready for more dynamic control? Explore [Conditional Statements](/promptl/syntax/conditionals) to complement your loops.