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Overview

Functions are the core of Simforge. Each function defines:
  • Inputs: The data your function accepts
  • Outputs: The structured data your function returns
  • Prompt: The instructions for the LLM
  • Provider: Which LLM to use (OpenAI, Anthropic, etc.)

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Creating a Function

  1. Navigate to Functions in the sidebar
  2. Click Create Function
  3. Enter a name for your function (e.g., ExtractName)
  4. Define your function using BAML syntax

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Example Function

class NameOutput {
  firstName string
  lastName string
}

function ExtractName(text: string) -> NameOutput {
  client "openai/gpt-4o"
  prompt #"
    Extract the first and last name from the following text:

    {{ text }}

    Return the name as JSON.
  "#
}

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Function Editor

The function editor provides:
  • Syntax Highlighting: BAML syntax is highlighted for readability
  • Error Checking: Syntax errors are shown inline
  • Auto-save: Changes are saved automatically as drafts
  • Version History: View and restore previous versions

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Editor Tabs

TabDescription
EditorWrite and edit your BAML code
TestRun your function with sample inputs
TracesView execution history for this function
VersionsBrowse and restore previous versions

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Testing Functions

Test your function directly in the portal:
  1. Open a function
  2. Click the Test tab
  3. Enter input values in the form
  4. Click Run
  5. View the output and execution details

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Test Inputs

Enter test inputs as JSON or use the form fields: 
{
  "text": "My name is John Doe and I work at Acme Corp."
}

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Versioning

Every time you save a function, a new version is created:
  • Draft: Unsaved changes (not deployed)
  • Published: The active version used by the SDK
  • Previous Versions: Historical versions you can restore

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Publishing Changes

  1. Make changes in the editor
  2. Click Save to create a draft
  3. Click Publish to make the version active

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Restoring a Version

  1. Open the Versions tab
  2. Find the version you want to restore
  3. Click Restore
  4. The version is copied to a new draft
  5. Review and publish when ready

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BAML Syntax

Functions are defined using BAML. Here are the key concepts:

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Classes

Define structured output types: 
class Person {
  firstName string
  lastName string
  age int?  // optional field
  email string?
}

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Enums

Define categorical outputs: 
enum Sentiment {
  POSITIVE
  NEGATIVE
  NEUTRAL
}

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Functions

Define the function signature and prompt: 
function ClassifySentiment(text: string) -> Sentiment {
  client "openai/gpt-4o"
  prompt #"
    Classify the sentiment of the following text as POSITIVE, NEGATIVE, or NEUTRAL:

    {{ text }}
  "#
}

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Clients

Configure which LLM provider to use: 
client "openai/gpt-4o"        // OpenAI GPT-4o
client "anthropic/claude-3"    // Anthropic Claude 3
client "openai/gpt-3.5-turbo" // OpenAI GPT-3.5 Turbo

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Best Practices

  • Descriptive Names: Use clear, descriptive function names like ExtractInvoiceData instead of Extract
  • Typed Outputs: Always define a class for your output to ensure type safety
  • Clear Prompts: Write clear, specific prompts with examples when needed
  • Test Thoroughly: Test with various inputs before publishing
  • Version Control: Use meaningful changes between versions