9 · Dependencies & unlocks

Real subjects have an order: you can’t grasp borrowing before ownership, or a derived rule before its axioms. alix lets a deck declare what it builds on, and uses that both to sequence your study and to gate decks until you’re ready.

Declaring prerequisites — % requires:

A deck names its prerequisites with % requires: lines in the header (repeatable):

% requires: rust-ownership
% requires: rust-references

# What does the borrow checker prevent?
    Aliasing a value while it's mutably borrowed.

A name resolves next to the requiring deck or in your decks directory, with or without the .txt. Like all directives these are plain comments, so adding or changing them never touches card progress. A missing prerequisite or a dependency cycle is treated as non-blocking — a broken edge never hides a deck.

Dependencies don’t change what you review

% requires: is about order and gating, not session contents. When you review (or browse) a deck, the session holds exactly that deck’s cards — prerequisites are never pulled in, so the mode/order/scheduler you study under is always the deck’s own. What dependencies shape is the picker’s dependency tree (foundations shown first) and, for a deck with a % source:, the exam gate below.

Editing without typos — alix deps

To change a deck’s prerequisites without hand-editing, use alix deps <deck> (alias alix require):

alix deps borrowing.txt

It opens the deck picker over your decks directory, pre-ticked to the current prerequisites: Space toggles, Enter saves (rewriting the % requires: lines), Esc cancels, and unticking everything clears them. Because the lines are comments, editing dependencies never disturbs card progress.

Unlocks

The same % requires: graph drives unlocks, with no extra syntax — and the gate is the exam, not drilling. You can review any deck at any time, in any order; what % requires: controls is exam order: a deck with a % source: can’t sit its exam until each of its sourced prerequisites has passed its own exam, and passing a foundation’s exam unlocks the exams that build on it. A source-less prerequisite has no exam to pass, so it never gates — its edge is just a suggested order in the tree. (A trace masters by finishing its walk — the walk is its exam — so it gates and unlocks like any sourced deck.)

In the picker a deck whose exam is locked shows a 🔒, but it stays drillable — only the exam waits on the prerequisites.

This is what turns a folder of decks into a curriculum: order the material by % requires:, and alix gates each step’s exam on passing the last. It’s the backbone of the AI exam’s notion of mastery (a later chapter) and of how alix explore lays out a generated learning plan.