Nock is a low-level homoiconic combinator language. It's so simple that its specification fits on a t-shirt. In some ways Nock resembles a nano-Lisp but its ambitions are more narrow. Most Lisps are one-layer: a practical language is to be created by extending a theoretically simple interpreter. The abstraction is simple and the implementation is practical. Unfortunately it's far more difficult to enforce both simplicity and practicality in an actual Lisp codebase. Hoon and Nock are two layers: Hoon, the practical layer, compiles itself to Nock, the simple layer. Your urbit runs in Vere, which includes a Nock interpreter, so it can upgrade Hoon over the network without downtime.

The Nock data model is quite simple. Every piece of data is a 'noun'. A noun is an atom or a cell. An atom is any unsigned integer. A cell is an ordered pair of nouns. Nouns are acyclic and expose no pointer equality test.

Further Reading