How to call Open AI's API with F# (GPT-4o)

AI is becoming an increasingly versatile tool in a developer's toolbelt. I'm currently looking to add some AI-powered features in my own projects I'm building with F# so here I'll share a simple example of integrating an F# script with Open AI's API - targeting the GPT-4o model.

Overview

For this example I'm building a very simple CLI tool. You run it, it makes the call, and outputs its results.

Program: F# CLI Script
Runtime: Dotnet 8 in a Docker container

I'm using a very simple prompt to prove this works - asking the AI to output a haiku about F#.

Prompt: Write a haiku about F#.
Example Response: Functional whispers, Type safety in gentle breeze, Code flows, clear and free.

Call Open AI API from F#

We'll be using the Open AI chat completions API (official docs) to give us a response. This is similar to a typical AI chatbot workflow - you give it a prompt, it returns a response.

The script itself is very simple:

Create an http client with an Auth Bearer token containing our API key
Build up our request / response data model
Create and send the request
Parse the response

Want the full project source code? HAMINIONs members get access to the project's repo including full source code / files.

Code:

open System 
open System.Net.Http
open System.Text 
open System.Text.Json

printfn "Hello from F#"

let apiKey = "YOUR_API_KEY_HERE"
let apiUrl = "https://api.openai.com/v1/chat/completions"

let client = new HttpClient()
client.DefaultRequestHeaders.Add("Authorization", $"Bearer {apiKey}")

let prompt = "Write a haiku about F#."

type ChatMessageApiDto = 
    {
        role: string
        content: string
    }

type ChatRequestApiDto = 
    {
        model: string  
        messages: ChatMessageApiDto list 
    }

type ChatResponseChoiceApiDto = 
    {
        message: ChatMessageApiDto
    }

type ChatResponseApiDto = 
    {
        choices: ChatResponseChoiceApiDto list
    }

let request = 
    {
        model = "gpt-4o-mini"
        messages = [
            {
                role = "user"
                content = prompt
            }
        ]
    }

(* # Make Request *)

let requestJson = 
    JsonSerializer.Serialize(request) 

printfn "Request: %A" requestJson

let requestContent = new StringContent(requestJson, Encoding.UTF8, "application/json") 

let response = 
    client.PostAsync(apiUrl, requestContent)
    |> Async.AwaitTask 
    |> Async.RunSynchronously 

let responseBody = 
    response.Content.ReadAsStringAsync()
    |> Async.AwaitTask
    |> Async.RunSynchronously
printfn "ResponseBody: %A" responseBody

let chatResponse = JsonSerializer.Deserialize<ChatResponseApiDto>(responseBody)
printfn "ChatResponse: %A" chatResponse

let generatedText = chatResponse.choices.[0].message.content
printfn "Final response: %s" generatedText

Example Outputs

Here I'll paste some example outputs to give you an idea of what it looks like when it's run:

Request:

{"model":"gpt-4o-mini","messages":[{"role":"user","content":"Write a haiku about F#."}]}

Response:

{
  "id": "chatcmpl-9nng4bclVFjOZlKnwQWBDPx8MP4gU",
  "object": "chat.completion",
  "created": 1721656060,
  "model": "gpt-4o-mini-2024-07-18",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "Functional whispers,  \nTypes and expressions entwined,  \nCode flows like clear streams."
      },
      "logprobs": null,
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 14,
    "completion_tokens": 17,
    "total_tokens": 31
  },
  "system_fingerprint": "fp_661538dc1f"
}

FinalResponse - the F# haiku:

Functional whispers,  
Types and expressions entwined,  
Code flows like clear streams.

I haven't experimented too much with available AI APIs and what they're capable of but I think there are some fun applications for adding some dynamism to software projects. I'll be doing more experiments in the coming weeks to see what I can build with them so stay tuned if you're interested in that.

Q: What are you using AI for in your dev workflow / projects?

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How to call Open AI's API with F# (GPT-4o)

Overview

Call Open AI API from F#

Example Outputs

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