An impl is an implementation of a function using an AI model (LLM or otherwise).


    client SomeClient
  • IMPL_TYPE: What type of AI model will be used. Currently must be llm
  • FUNCTION_NAME: The name of the function this is an implementation of
  • Name: The name of the impl (can be any [a-zA-Z], numbers or _)


Depending on the IMPL_TYPE, additional properties may exist.

clientstringThe name of the client this impl will use. The type of the client must match the type of the impl (both llm). See ClientYES
adapterSee AdaptersModify a type temporarily for the use in the impl without exposing it to the buisness logic. e.g. force an llm to extract extra fields not specified earlier. This is an advanced tool!NO

impl types

✅ llm

llm models are those which take a prompt (string) and return a string. For example, GPT-3, GPT-J, etc. They may also return some other metadata (e.g. logprobs, stop_reason, etc.)

promptstringThe string passed into the LLM. You can compose this this variables and other template types. See Prompt EngineeringYES

❌ probability

Not supported yet.

probability models are those which take in any type, and return float[] of a fixed length. For example, BERT, etc.And yes we know technically LLMs do this under the hood, but most practical LLMs outputs are synthesized into a string.


Sentiment Analysis


Defining in baml

{#input} and {#print_enum(Sentiment)} are template variables injected into the prompt. See Prompt Engineering for more details.

impl<llm, GetSentiment> my_version {
    client GPT35Client
    prompt #"
        Given a sentence, return the sentiment.




// Define the function
function GetSentiment {
    input string
    output Sentiment

// Define the enum for sentiment
enum Sentiment {

// Use OpenAI's GPT-3.5 turbo model
client<llm> GPT35Client {
    provider baml-openai-chat
    options {
        model gpt-3.5-turbo

Using the generated code

from baml_client import baml as b
from baml_client.baml_types import Sentiment

async def pipeline(arg: str) -> str:
    sentiment = await b.GetSentiment(arg)

    if sentiment == Sentiment.Positive:
        return "I'm glad you're having a good day!"
    elif sentiment == Sentiment.Negative:
        return "I'm sorry to hear that."
        return "I see it's just a normal day for you."


Calling a specific implementation of a function

If you provide multiple implementations of a given function in BAML (e.g. impl<llm, Fn> my_version and impl<llm, Fn> dev_version), you can specify which should be used by default:

function GetSentiment {
    input string
    output Sentiment
    default_impl my_version

Alternatively, you can also directly call a specific implementation:

await b.GetSentiment.get_impl('my_version').run(arg)