giles
99753580b4
Salvaged from worktree-agent-* branches killed during sx-tree MCP outage: - lua: tokenizer + parser + phase-2 transpile (~157 tests) - prolog: tokenizer + parser + unification (72 tests, plan update lost to WIP) - forth: phase-1 reader/interpreter + phase-2 colon/VARIABLE (134 tests) - erlang: tokenizer + parser (114 tests) - haskell: tokenizer + parse tests (43 tests) Cherry-picked file contents only, not branch history, to avoid pulling in unrelated ocaml-vm merge commits that were in those branches' bases.
108 lines
6.5 KiB
Markdown
108 lines
6.5 KiB
Markdown
# Erlang-on-SX: actors on delimited continuations
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The headline showcase for the SX runtime. Erlang is built around the **one** primitive — lightweight processes with mailboxes and selective receive — that delimited continuations implement natively. Most Erlang implementations ship a whole VM (BEAM) for this; on SX each process is a pair of continuations and the scheduler is ~50 lines of SX.
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End-state goal: spawn a million processes, run the classic **ring benchmark**, plus a mini gen_server OTP subset and a test corpus of ~150 programs.
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## Scope decisions (defaults — override by editing before we spawn)
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- **Syntax:** Erlang/OTP 26 subset. No preprocessor, no parse transforms.
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- **Conformance:** not BEAM-compat. "Looks like Erlang, runs like Erlang, not byte-compatible." We care about semantics, not BEAM bug-for-bug.
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- **Test corpus:** custom — ring, ping-pong, fibonacci-server, bank-account-server, echo-server, plus ~100 hand-written tests for patterns/guards/BIFs. No ISO Common Test.
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- **Binaries:** basic bytes-lists only; full binary pattern matching deferred.
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- **Hot code reload, distribution, NIFs:** out of scope entirely.
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## Ground rules
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- **Scope:** only touch `lib/erlang/**` and `plans/erlang-on-sx.md`. Don't edit `spec/`, `hosts/`, `shared/`, `lib/js/**`, `lib/hyperscript/**`, `lib/lua/**`, `lib/prolog/**`, `lib/forth/**`, `lib/haskell/**`, `lib/stdlib.sx`, or `lib/` root. Erlang primitives go in `lib/erlang/runtime.sx`.
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- **SX files:** use `sx-tree` MCP tools only.
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- **Commits:** one feature per commit. Keep `## Progress log` updated and tick roadmap boxes.
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## Architecture sketch
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```
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Erlang source
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│
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▼
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lib/erlang/tokenizer.sx — atoms, vars, tuples, lists, binaries, operators
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│
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▼
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lib/erlang/parser.sx — AST: modules, functions with clauses, patterns, guards
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│
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▼
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lib/erlang/transpile.sx — AST → SX AST (entry: erlang-eval-ast)
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│
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▼
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lib/erlang/runtime.sx — scheduler, processes, mailboxes, BIFs
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```
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Core mapping:
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- **Process** = pair of delimited continuations (`on-receive`, `on-resume`) + mailbox list + pid + links
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- **Scheduler** = round-robin list of runnable processes; cooperative yield on `receive`
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- **`spawn`** = push a new process record, return its pid
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- **`send`** = append to target mailbox; if target is blocked on receive, resume its continuation
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- **`receive`** = selective — scan mailbox for first matching clause; if none, `perform` a suspend with the receive pattern; scheduler resumes when a matching message arrives
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- **Pattern matching** = SX `case` on tagged values; vars bind on match
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- **Guards** = side-effect-free predicate evaluated after unification
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- **Immutable data** = native
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- **Links / monitors / exit signals** = additional process-record fields, scheduler fires exit signals on death
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## Roadmap
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### Phase 1 — tokenizer + parser
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- [x] Tokenizer: atoms (bare + single-quoted), variables (Uppercase/`_`-prefixed), numbers (int, float, `16#HEX`), strings `"..."`, chars `$c`, punct `( ) { } [ ] , ; . : :: ->` — **62/62 tests**
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- [x] Parser: module declarations, `-module`/`-export`/`-import` attributes, function clauses with head patterns + guards + body — **52/52 tests**
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- [x] Expressions: literals, vars, calls, tuples `{...}`, lists `[...|...]`, `if`, `case`, `receive`, `fun`, `try/catch`, operators, precedence
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- [ ] Binaries `<<...>>` — not yet parsed (deferred to Phase 6)
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- [x] Unit tests in `lib/erlang/tests/parse.sx`
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### Phase 2 — sequential eval + pattern matching + BIFs
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- [ ] `erlang-eval-ast`: evaluate sequential expressions
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- [ ] Pattern matching (atoms, numbers, vars, tuples, lists, `[H|T]`, underscore, bound-var re-match)
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- [ ] Guards: `is_integer`, `is_atom`, `is_list`, `is_tuple`, comparisons, arithmetic
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- [ ] BIFs: `length/1`, `hd/1`, `tl/1`, `element/2`, `tuple_size/1`, `atom_to_list/1`, `list_to_atom/1`, `lists:map/2`, `lists:foldl/3`, `lists:reverse/1`, `io:format/1-2`
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- [ ] 30+ tests in `lib/erlang/tests/eval.sx`
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### Phase 3 — processes + mailboxes + receive (THE SHOWCASE)
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- [ ] Scheduler in `runtime.sx`: runnable queue, pid counter, per-process state record
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- [ ] `spawn/1`, `spawn/3`, `self/0`
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- [ ] `!` (send), `receive ... end` with selective pattern matching
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- [ ] `receive ... after Ms -> ...` timeout clause (use SX timer primitive)
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- [ ] `exit/1`, basic process termination
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- [ ] Classic programs in `lib/erlang/tests/programs/`:
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- [ ] `ring.erl` — N processes in a ring, pass a token around M times
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- [ ] `ping_pong.erl` — two processes exchanging messages
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- [ ] `bank.erl` — account server (deposit/withdraw/balance)
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- [ ] `echo.erl` — minimal server
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- [ ] `fib_server.erl` — compute fib on request
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- [ ] `lib/erlang/conformance.sh` + runner, `scoreboard.json` + `scoreboard.md`
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- [ ] Target: 5/5 classic programs + 1M-process ring benchmark runs
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### Phase 4 — links, monitors, exit signals
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- [ ] `link/1`, `unlink/1`, `monitor/2`, `demonitor/1`
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- [ ] Exit-signal propagation; trap_exit flag
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- [ ] `try/catch/of/end`
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### Phase 5 — modules + OTP-lite
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- [ ] `-module(M).` loading, `M:F(...)` calls across modules
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- [ ] `gen_server` behaviour (the big OTP win)
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- [ ] `supervisor` (simple one-for-one)
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- [ ] Registered processes: `register/2`, `whereis/1`
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### Phase 6 — the rest
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- [ ] List comprehensions `[X*2 || X <- L]`
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- [ ] Binary pattern matching `<<A:8, B:16>>`
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- [ ] ETS-lite (in-memory tables via SX dicts)
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- [ ] More BIFs — target 200+ test corpus green
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## Progress log
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_Newest first._
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- **parser green** — `lib/erlang/parser.sx` + `parser-core.sx` + `parser-expr.sx` + `parser-module.sx`. 52/52 in `tests/parse.sx`. Covers literals, tuples, lists (incl. `[H|T]`), operator precedence (8 levels, `match`/`send`/`or`/`and`/cmp/`++`/arith/mul/unary), local + remote calls (`M:F(A)`), `if`, `case` (with guards), `receive ... after ... end`, `begin..end` blocks, anonymous `fun`, `try..of..catch..after..end` with `Class:Pattern` catch clauses. Module-level: `-module(M).`, `-export([...]).`, multi-clause functions with guards. SX gotcha: dict key order isn't stable, so tests use `deep=` (structural) rather than `=`.
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- **tokenizer green** — `lib/erlang/tokenizer.sx` + `lib/erlang/tests/tokenize.sx`. Covers atoms (bare, quoted, `node@host`), variables, integers (incl. `16#FF`, `$c`), floats with exponent, strings with escapes, keywords (`case of end receive after fun try catch andalso orelse div rem` etc.), punct (`( ) { } [ ] , ; . : :: -> <- <= => << >> | ||`), ops (`+ - * / = == /= =:= =/= < > =< >= ++ -- ! ?`), `%` line comments. 62/62 green.
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## Blockers
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- _(none yet)_
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