Extensions
An extension puts another language on the engine, or another storage backend underneath it. Four ship today.
| Extension | What you get |
|---|---|
| PyMeTTa | write MeTTa programs in Python, via the metta package |
| MeTTa-node | write them in TypeScript, running on swipl-wasm inside Node |
| CMeTTa | embed the engine in a C program |
| MORK | store spaces in a Rust trie instead of in memory |
The first three are languages you write programs in, so each has a tutorial that starts from an empty directory and ends at a running program: Python, TypeScript, C. MORK is storage, so there is nothing to write in it and it has a single page.
How one is put together
An extension is a folder under extensions/ containing a file called extension.pl. That file holds facts, not code: the engine reads it and never executes it.
The facts that matter most say which side loads what. entry(engine, File) means the engine consults File when it boots. entry(host, File) means the other language's runtime consults it instead. An extension can declare either or both:
- Python declares both, so the engine can call into Python and Python can drive the engine.
- C declares both as well, in one file.
- TypeScript declares only
host. The engine records that the extension exists and never loads anything, because the TypeScript side owns its own copy of the engine. - MORK declares only
engine. There is no MORK program to run; the engine reaches down to it for storage.
When something is missing
If an extension's prerequisites are absent, it loads nothing and prints nothing.
If it is built but broken, it raises, because that is a real fault.
A library that depends on one asks for it explicitly:
!(require-extension! mork)If it is not there, the refusal names what is missing and gives you the command that builds it.
Adding your own
The contract for adding an extension covers what goes in the folder: the vocabulary of the control file, the five scripts every extension provides and the exit code they agree on, and where tests and benchmarks live.
It also covers the three choices you make: which direction your extension faces, whether a definition is called or compiled, and what a value looks like when it crosses.
Extending the engine is the other half: the nine points the engine offers, and what each one costs.