Running MeTTa Code

MeTTa scripts can be run in several ways depending on whether you are doing research, building an agent, or integrating with Python.

The MeTTa Interpreter

The primary way to run code is using the official MeTTa interpreter (often part of the Hyperon-core package).

Running a script from terminal

metta my_script.metta

The REPL (Read-Eval-Print Loop)

You can enter an interactive mode to test patterns on the fly:

metta --repl

Basic Structure of a Program

A MeTTa program generally consists of:

1. Atoms added to the AtomSpace.
2. Rules defined using the = symbol.
3. Queries executed via an implicit match or an explicit call.

Example: Hello World

;; Define a rule
(= (greet $name) (format "Hello, {}!" $name))

;; Call the rule
!(greet "AGI Researcher")

The ! prefix tells the interpreter to "Execute/Evaluate this immediately."

Integrating with Python

Since most AI research is in Python, MeTTa provides a seamless bridge.

from hyperon import MeTTa

# Initialize the interpreter
m = MeTTa()

# Run some MeTTa code directly from Python
result = m.run('!(+ 2 2)')
print(result) # Output: [[4]]

Error Handling and Debugging

Unlike traditional languages, "Errors" in MeTTa often result in Failing to Match. If you try to call a function that doesn't exist, MeTTa won't crash; it will simply return an "Empty Set" because no rewrite rule was found.

Debugging Tip: Use the (Match (AtomSpace) ...) query to inspect the state of your knowledge base if your results aren't what you expect.

Next: Example Programs