The engine

The rest of this site is written from the Python surface looking in. These five pages are written from the engine looking out: what its extension points are and what each costs, which forms it gives meaning to and why, the wire every atom crosses on, what it costs against upstream PeTTa, and how to work on the repository itself.

Each page is the repository document of the same name, published here rather than copied, so the version you read is the committed one.

• Extending the engine is the map of nine extension points, ordered by measured cost. A translator rule, a C foreign predicate and a Prolog grounded predicate all cost about what a MeTTa function costs; a Python operation costs the janus crossing. The page also covers reader token classes, space providers, atom hooks, custom matchers, and the extension.pl control file that makes a folder under extensions/ an extension the engine reads.
• The kernel is the ledger of the 58 heads the translator gives a meaning of their own, each classified against minimal MeTTa's state-free structural core as a counterpart, a follow-up, or a divergence this engine chose. A head fused into the compiler rather than expressed as a prelude rule has to say what the fusion buys, with numbers.
• The wire codec is the tagged form every atom crosses in, and what a new binding in a new language has to implement.
• Performance is what this engine costs against upstream PeTTa over the example corpus, measured in retired instructions net of each engine's boot: the median program, the boot this engine pays for what it loads, and the programs where it is dearer, named with their causes.
• Developing is the contributor side: the interpreter and SWI-Prolog versions, check.sh and what its two tiers mean, and the measurement rules that decide whether a performance claim is evidence.

The extension points themselves are declared in engine/ext_points.pl, each with the kind of thing it is (event, ownership, declaration, service), and that file is the contract. The contract covers the same attachment story from the backend author's side, in the guide's voice.