LLMGleam

A Gleam library for interacting with Large Language Model APIs. Currently supports Google’s Gemini, OpenAI’s GPT, and Anthropic’s Claude APIs with a clean, type-safe interface.

Features

• 🔒 Type-safe: Leverages Gleam’s type system for reliable API interactions
• 🌟 Clean API: Fluent builder pattern for constructing requests
• 🔌 Extensible: Designed to support multiple LLM providers
• 🛠️ Tool calling: Define and execute function tools with GPT, Claude, and Gemini
• ⚡ Async: Built on Gleam’s concurrent model

Installation

gleam add llmgleam

Quick Start

import gleam/option
import llmgleam
import llmgleam/client
import llmgleam/messages

pub fn main() {
  // Create a client
  let client = llmgleam.new_client(client.Gemini, "your-api-key-here")

  // Get completion using the builder pattern
  let result =
    client
    |> client.request()
    |> client.with_message(messages.user("Hello, how are you?"))
    |> client.completion("gemini-2.5-flash")

  case result {
    Ok(completion) -> {
      io.println("Response: " <> option.unwrap(completion.content, ""))
    }
    Error(error) -> {
      io.println("Error: " <> string.inspect(error))
    }
  }
}

API Reference

Creating a Client

import llmgleam
import llmgleam/client

// For Gemini
let gemini_client = llmgleam.new_client(client.Gemini, "your-gemini-api-key")

// For GPT
let gpt_client = llmgleam.new_client(client.GPT, "your-openai-api-key")

// For Claude
let claude_client = llmgleam.new_client(client.Claude, "your-anthropic-api-key")

Building Requests

The library uses a fluent builder pattern for constructing requests:

import llmgleam/client
import llmgleam/messages

let completion =
  client
  |> client.request()
  |> client.with_message(messages.user("Hello, how are you?"))
  |> client.with_system_instruction("You are a helpful assistant")
  |> client.completion("gemini-2.5-flash")

Messages

import llmgleam/messages

// Create a user message
let user_msg = messages.user("Hello, how are you?")

// System instructions are added via with_system_instruction

Tool Calling

Function tools use a typed JSON Schema builder for their arguments. Tool arguments returned by the model are JSON-encoded strings and should be decoded and validated before use with tools.decode_arguments and a Gleam decoder.

import llmgleam/client
import llmgleam/messages
import llmgleam/schema
import llmgleam/tools

let weather_tool =
  tools.function(
    name: "get_weather",
    description: "Get the current weather for a location",
    parameters: schema.parameters([
      schema.property(
        "location",
        schema.string()
        |> schema.described("The city and country, such as Paris, France"),
      ),
    ]),
  )

let request =
  gpt_client
  |> client.request()
  |> client.with_message(messages.user("What is the weather in Paris?"))
  |> client.with_tool(weather_tool)

let assert Ok(first) = client.completion(request, "gpt-5-nano")
let assert [call, ..] = first.tool_calls

// Run the function in your application, then return its output to GPT.
let output = tools.output(call, "{\"temperature\":18,\"unit\":\"celsius\"}")
let assert Ok(continued) = client.continue_from(request, first)
let final =
  continued
  |> client.with_tool_output(output)
  |> client.completion("gpt-5-nano")

A response can contain text, tool calls, or both. Text is available as completion.content: Option(String). Models can request multiple calls, in which case all outputs should be added with client.with_tool_outputs before continuing.

Tool calling supports GPT through OpenAI’s Responses API, Claude through Anthropic’s Messages API, and Gemini through the GenerateContent API. GPT continues from a response ID; Claude and Gemini continue by sending prior tool calls and tool results back in conversation order. Gemini thought signatures and function-call IDs are preserved automatically. The same client API is used for all providers.

Functions

1. llmgleam.new_client(provider: Provider, api_key: String) -> Client

   Creates a new LLM client for the specified provider.

2. client.request(client: Client) -> Request

   Initializes a new request builder from a client.

3. client.with_message(request: Request, message: Message) -> Request

   Adds a message to the request.

4. client.with_system_instruction(request: Request, instruction: String) -> Request

   Adds a system instruction to the request.

5. client.completion(request: Request, model: String) -> Result(Completion, CompletionError)

   Executes the request and returns text, tool calls, or both.

6. client.with_tool(request: Request, tool: Tool) -> Request

   Adds a function tool to a GPT request.

7. client.continue_from(request: Request, completion: Completion) -> Result(Request, CompletionError)

   Starts the next turn of a GPT, Claude, or Gemini tool-calling exchange.

Supported Providers

Google Gemini

• Provider: client.Gemini
• Authentication: API key via Google AI Studio

OpenAI GPT

• Provider: client.GPT
• Authentication: API key via OpenAI

Anthropic Claude

• Provider: client.Claude
• Authentication: API key via Anthropic

Example with System Instructions

import llmgleam
import llmgleam/client
import llmgleam/messages

let client = llmgleam.new_client(client.Gemini, "your-api-key")

let completion =
  client
  |> client.request()
  |> client.with_message(messages.user("hello, how are you?"))
  |> client.with_system_instruction("you are a helpful conversationalist")
  |> client.completion("gemini-2.5-flash")

Development

Running Tests

gleam test

For integration tests (requires API keys):

RUN_INTEGRATION_TESTS=1 GEMINI_KEY=your-key GPT_KEY=your-key gleam test

Building

gleam build

Contributing

Contributions are welcome! Areas for improvement:

• Add support for OpenAI GPT models
• Add support for Gemini API
• Add support for Gemini through vertex.ai
• Add support for Anthropic Claude
• Add streaming support
• Add function calling support for GPT, Claude, and Gemini
• Add image/multimodal support

License

This project is licensed under the MIT License - see the LICENSE file for details.