> ## Documentation Index
> Fetch the complete documentation index at: https://liquidai-alay2shah-sync-notebook-snippets.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Utilities

> API reference for error handling and utilities in the LEAP iOS SDK

## Errors

Errors are surfaced as `LeapError` values. The most common cases are:

* `LeapError.modelLoadingFailure`: Problems reading or validating the model bundle.
* `LeapError.generationFailure`: Unexpected native inference errors.
* `LeapError.promptExceedContextLengthFailure`: Prompt length exceeded the configured context size.
* `LeapError.serializationFailure`: JSON encoding/decoding problems when working with chat history or function calls.

Handle thrown errors with `do` / `catch` when using async streams, or use the `onErrorCallback` in the lower-level API.

## Putting it together

```swift theme={"theme":{"light":"github-light","dark":"github-dark"}}
let runner = try await Leap.load(url: bundleURL)
let conversation = runner.createConversation(systemPrompt: "You are a travel assistant.")

conversation.registerFunction(weatherFunction)

var options = GenerationOptions(temperature: 0.8)
try options.setResponseFormat(type: TripRecommendation.self)

let userMessage = ChatMessage(
  role: .user,
  content: [.text("Plan a 3-day trip to Kyoto with food highlights")]
)

for try await response in conversation.generateResponse(
  message: userMessage,
  generationOptions: options
) {
  process(response)
}
```

Refer to the [Quick Start](./ios-quick-start-guide) for end-to-end project setup, [Function Calling](./function-calling) for tool invocation, and [Constrained Generation](./constrained-generation) for structured outputs.