rose-ash/plans/agent-briefings/elixir-loop.md

# elixir-on-sx loop agent (single agent, queue-driven)

Role: iterates `plans/elixir-on-sx.md` forever. **Elixir on the CEK/VM** — the
companion to `lib/erlang/`. Most runtime semantics are Erlang's (BEAM); the
chisel is the *Elixir-specific* surface: the macro system (`quote`/`unquote`),
`|>`, `with`, `defmodule`/`def`/`defp`, protocol dispatch, structs. One feature
per commit.

```
description: elixir-on-sx queue loop
subagent_type: general-purpose
run_in_background: true
isolation: worktree
```

## Prerequisites — check before starting

1. **lib-guest lex + pratt present** — Elixir's tokenizer/parser consume
   `lib/guest/lex.sx` + `lib/guest/pratt.sx`.
2. **`lib/erlang/` present** — Phase 2 reuses Erlang's pattern-match engine for
   `=`, function heads, and `case`. Do not re-implement unification; import it.
3. **ADT primitive (`define-type` + `match`)** in the SX core — needed for structs
   (Phase 5). Track via `plans/sx-improvements.md`.

**Pre-flight:**
```
ls /root/rose-ash/lib/guest/lex.sx /root/rose-ash/lib/guest/pratt.sx /root/rose-ash/lib/erlang/runtime.sx
```
If lib-guest or lib/erlang is missing, stop and record a Blockers entry. (The ADT
primitive is only needed at Phase 5 — start earlier phases without it.)

## Prompt

You are the sole background agent working `/root/rose-ash/plans/elixir-on-sx.md`,
in an isolated git worktree on branch `loops/elixir`, forever, one commit per
feature. Push to `origin/loops/elixir` after every commit. Never touch `main` or
`architecture`.

## Restart baseline — check before iterating

1. Read `plans/elixir-on-sx.md` — Roadmap + Progress log + Blockers tell you where
   you are.
2. Run the pre-flight. Record any missing prerequisite in Blockers.
3. `ls lib/elixir/` — pick up from the most advanced file. No dir → Phase 1.
4. If `lib/elixir/tests/*.sx` exist, run them via the epoch protocol against
   `sx_server.exe` (`SX_SERVER=/root/rose-ash/hosts/ocaml/_build/default/bin/sx_server.exe`).
   Green before new work.

## The queue

Phase order per `plans/elixir-on-sx.md`:

- **Phase 1** — tokenizer + parser (`:atom`, charlists, `<>`, `|>`, `do/end`)
- **Phase 2** — transpile basic Elixir (no macros/processes): arithmetic, pattern
  match (reuse Erlang engine), `def`/`defp` clause dispatch, modules, `|>`, `with`,
  `for`, `fn`/`&`, `cond`/`case`, interpolation, keyword lists/maps/tuples
- **Phase 3** — **macro system** (`quote`/`unquote`/`unquote_splicing`, `defmacro`,
  two-pass expand, `use`/`import`/`alias`) — the headline phase
- **Phase 4** — protocols (`defprotocol`/`defimpl`, dispatch, `Enumerable` etc.)
- **Phase 5** — structs + behaviours (`defstruct`, `%Mod{}`, `@behaviour`)

Within a phase, pick the checkbox with the best tests-per-effort ratio.
Every iteration: implement → test → commit → tick `[ ]` → Progress log → push → next.

## Chisel discipline — the macro system

Elixir earns its place by exercising **homoiconic macros on a non-Lisp surface
syntax**. `quote do … end` must produce Elixir AST as SX list structure, and
`defmacro` must run at expansion time receiving/returning that AST. The two-pass
model (collect defs, then expand before transpile) is the crux — get it right in
Phase 3. If macro hygiene exposes an SX gensym/quoting gap, that's a substrate
note (Blockers), not an Elixir fix.

## Ground rules (hard)

- **Scope:** only `lib/elixir/**` and `plans/elixir-on-sx.md`. Do **not** edit
  `spec/`, `hosts/`, `shared/`, `lib/guest/**` (read-only), `lib/erlang/**`
  (read-only — import its pattern engine), or other `lib/<lang>/`.
- **Reuse, don't re-implement.** Consume `lib/guest/` (lex, pratt) and `lib/erlang/`
  (pattern matching) wherever they cover a need.
- **Don't patch the substrate from this loop.** Failing core behavior → failing
  test + Blockers entry + stop.
- **NEVER call `sx_build`** (600s watchdog). Broken `sx_server.exe` → Blockers, stop.
- **SX files:** `sx-tree` MCP tools ONLY; `sx_validate` after every edit. Never
  `Edit`/`Read`/`Write` on `.sx`. They take `file:` not `path:`.
- **Worktree:** commit, then push `origin/loops/elixir`. Never `main`/`architecture`.
- **Commits:** one feature per commit. Short factual messages
  (`elixir: |> pipe desugaring + 6 tests`).
- **Plan file:** Progress log (newest first) + tick boxes every commit.
- **Blocked 2 iterations on one issue → Blockers entry, move on.**

## Elixir-specific gotchas

- **Everything is an expression; blocks return their last value.** `do/end` is a
  block, not a statement list — map to SX `(begin …)`.
- **`|>` is transpile-time sugar:** `a |> f(b)` → `f(a, b)` (first-arg injection),
  resolved before evaluation — not a runtime combinator.
- **`with` short-circuits on the first `<-` mismatch to `else`** — desugar to nested
  pattern-matched lets with an escape, not to `and`.
- **Maps vs keyword lists:** `%{k: v}` → SX dict; `[k: v]` → SX list of `{:k v}`
  (ordered, dup keys allowed). Don't conflate them.
- **Atoms are not strings** — `:atom` is its own type; keep them distinct from
  string values even though SX keywords collapse to strings.
- **Macro args arrive as AST, not values** — `defmacro` receives quoted forms;
  evaluate `unquote` islands only.

## General gotchas (all loops)

- SX `do` = R7RS iteration; use `begin` for multi-expr sequences.
- `cond`/`when`/`let` clauses evaluate only the last expr — wrap multiples in `begin`.
- `let` is parallel — nest `let`s when one binding references an earlier one.
- `env-bind!` creates a binding; `env-set!` mutates an existing one.
- Namespace-prefix guest helpers (`ex/…`) — short/host-colliding names get shadowed.
- Shell heredoc `||` gets eaten — escape or use `case`.

## Style

- No comments in `.sx` unless non-obvious. No new planning docs — update the plan.
- Short, factual commit messages. One feature per iteration. Commit. Log. Push. Next.

Go. Run the pre-flight. If lib-guest or lib/erlang is missing, stop and report.
Otherwise read the plan, find the first unchecked `[ ]`, implement it.