Function Calling

Function calling with a Large Language Model (LLM) is a powerful feature that allows you to define functions that the LLM can call. The LLM will determine if and when a function is called.

There are many use cases for function calling. Here are few that we've implemented in our Angular applications:

Providing data to the LLM from state or an Angular service.
Performing tasks on behalf of the user.
Dispatching NgRx actions that are AI scoped that perform tasks or provide suggestions.

Demo

Example

Run the function calling example in Stackblitz

A few notes:

First, you will need an OpenAI API key.
Try the prompt: "Who am I?". That will invoke the getUser function.
Try the prompt: "Show me all the lights". This will invoke the getLights function.
Try the prompt: "Turn off all lights". This will invoke the controlLights function.

Defining a Function

Hashbrown provides the function for defining functions that the LLM can invoke.

createTool({
  name: 'getUser',
  description: 'Get information about the current user',
  handler: () => {
    const authService = inject(AuthService);
    return authService.getUser();
  },
});

Let's break down the example above:

name: The name of the function that the LLM will call.
description: A description of what the function does. This is used by the LLM to determine if it should call the function.
handler: The function that will be called when the LLM invokes the function. This is where you can perform any logic you need, such as fetching data from a service or performing a task. The function is invoked with an AbortSignal and is expected to return a Promise of the Result.

The method signature for a handler is:

(abortSignal: AbortSignal) => Promise<Result>;

Functions with Arguments

hashbrown's enables Angular developers to define functions that require arguments by specifying the schema. The LLM will invoke the function with the specified arguments.

We'll be using Skillet - hasbrown's LLM-optimized schema language - for defining the function arguments. Let's look at an example function that enables the LLM to control the lights in our smart home client application.

createToolWithArgs({
  name: 'controlLight',
  description: 'Control a light',
  schema: s.object('Control light input', {
    lightId: s.string('The id of the light'),
    brightness: s.number('The brightness of the light'),
  }),
  handler: async (input) =>
    this.lightsStore.updateLight(input.lightId, {
      brightness: input.brightness,
    }),
});

Let's review the code above.

name: The name of the function that the LLM will call.
description: A description of what the function does. This is used by the LLM to determine if it should call the function.
schema: The schema that defines the arguments that the function requires. This is where you can define the input parameters for the function using Skillet.
handler: The function that will be called when the LLM invokes the function. This is where you can perform any logic you need, such as fetching data from a service or performing a task. The function is invoked with an AbortSignal and is expected to return a Promise of the Result.

In this example, we expect that the input will be an object with the properties lightId and brightness, which are defined in the schema.

Note that the input arguments are strongly-typed based on the provided schema.

Providing the Functions

The next step is to provide the tools when using hashbrown's resource-based APIs.

@Component({
  selector: 'app-chat',
  providers: [LightsStore],
  template: ` <!-- omitted for brevity - full code in stackblitz example --> `,
})
export class ChatComponent {
  lightsStore = inject(LightsStore);

  chat = chatResource({
    model: 'gpt-4.1',
    prompt: 'You are a helpful assistant that can answer questions and help with tasks',
    tools: [
      createTool({
        name: 'getUser',
        description: 'Get information about the current user',
        handler: () => {
          const authService = inject(AuthService);
          return authService.getUser();
        },
      }),
      createTool({
        name: 'getLights',
        description: 'Get the current lights',
        handler: async () => this.lightsStore.entities(),
      }),
      createToolWithArgs({
        name: 'controlLight',
        description: 'Control a light',
        schema: s.object('Control light input', {
          lightId: s.string('The id of the light'),
          brightness: s.number('The brightness of the light'),
        }),
        handler: async (input) =>
          this.lightsStore.updateLight(input.lightId, {
            brightness: input.brightness,
          }),
      }),
    ],
  });

  sendMessage(message: string) {
    this.chat.sendMessage({ role: 'user', content: message });
  }
}

Let's review the code above.

First, we define the tools array in the chatResource configuration.
We use the and functions to define the functions that the LLM can call.
The handler functions are defined to perform the necessary logic, such as fetching data from services or updating the state.
Finally, we can use the sendMessage method to send a message to the LLM, which can then invoke the defined functions as needed.

Conclusion

Function calling is a powerful feature that allows you to define functions that the LLM can invoke. By using hashbrown's and functions, you can easily define functions with or without arguments that the LLM can call.