REPL: `main.janet` initializes context and sets current ns to "user". `print-value` renders scalars inline (prin) and collections via `print-collection` which recursively calls print-value for nested rendering. Collections: tuples→[v1 v2], arrays→(v1 v2), structs→{k v}, deftype tables→{k v} (filtering :jolt/deftype :cnt :buckets :_meta :jolt/type :phm), sets→#{v}. Jolt symbol structs render as `name` or `ns/name`.
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REPL collection rendering: print-value in main.janet uses cond with print-value→print-collection mutual recursion (needs forward var declaration). Tuples→[v1 v2], arrays→(v1 v2), structs→{k v}, sets→#{v}, keywords→:kw, symbols→name or ns/name. Use prin for scalars, print only after collection closing bracket. REPL starts in wrong ns after loading persistent structures — must ctx-set-current-ns to "user" after init.
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fn* special form dispatch: fn* form emitted by macros MUST be @[...] (array) to enter eval-list's special form match. If wrapped in [...] (tuple), eval-form hits the (tuple? form) branch which maps over items instead of dispatching fn*. Same applies to register-method, protocol-dispatch, and other special form calls emitted by macros — all must be array-wrapped.
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Janet's struct? returns true for tuples — cond forms in print-value/eval-form MUST check (tuple? x) before (struct? x) or (get x :key). Otherwise Janet sees a tuple, says yes to struct?, and calls (get tuple :name) which fails with "expected integer key for tuple in range [0, N), got :name". This hit us in print-value rendering and eval-form struct handling.
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Protocol system: Type registry in context env (:type-registry) maps type-tag→proto-name→method-name→fn. Three dispatch special forms: protocol-dispatch (resolves method via registry or reified methods), register-method (stores impl in registry), make-reified (creates anonymous object with :jolt/protocol-methods). fn* forms emitted by extend-type/extend-protocol MUST be @[...] (array) for eval-list dispatch. Protocols are maps with :jolt/type :jolt/protocol and :methods map.