rose-ash/plans/lua-on-sx.md

Lua-on-SX: Lua 5.1 on the CEK/VM

Compile Lua 5.1 AST to SX AST; the existing CEK evaluator runs it. Same architecture as plans/js-on-sx.md — reuse SX semantics wherever they fit, only shim the Lua-specific parts (tables/metatables, nil/false-only-falsy, multi-return, coroutines via perform/resume).

End-state goal: 100% of PUC-Rio Lua 5.1.5 test suite. Running as a long-lived background agent that drives the scoreboard up one failure-mode at a time, like lib/js/.

Ground rules

• Scope: only touch lib/lua/** and plans/lua-on-sx.md. Do not edit spec/, hosts/, shared/, lib/js/**, lib/hyperscript/**, lib/prolog/**, lib/stdlib.sx, or anything in lib/ root. Lua-specific primitives go in lib/lua/runtime.sx.
• Shared-file issues go under "Blockers" below with a minimal repro; do not fix from this loop.
• SX files: use sx-tree MCP tools only (never Edit/Read/Write on .sx files). sx_write_file for new files, path/pattern edits for changes.
• Architecture: Lua source → Lua AST → SX AST → CEK. No standalone Lua evaluator.
• Commits: one feature per commit. Keep ## Progress log updated (dated entries, newest first) and tick boxes in the roadmap.

Architecture sketch

Lua source text
    │
    ▼
lib/lua/tokenizer.sx     — numbers, strings (short + long [[…]]), idents, ops, comments
    │
    ▼
lib/lua/parser.sx        — Lua AST as SX trees, e.g. (lua-for-num i a b c body)
    │
    ▼
lib/lua/transpile.sx     — Lua AST → SX AST (entry: lua-eval-ast)
    │
    ▼
existing CEK / VM

Runtime shims in lib/lua/runtime.sx: lua-truthy?, string coercion for ../arithmetic, table ops (array + hash part), metatable dispatch, pcall/error bridge, string/math/table libs.

Roadmap

Each item: implement → tests → tick box → update progress log.

Phase 1 — tokenizer + parser

• Tokenizer: numbers (int, float, hex), strings (short + long [[…]]), idents, keywords, operators, comments (--, --[[…]])
• Parser: blocks, local, if/elseif/else/end, while, numeric for, function, return, expressions, table constructors, indexing (., []), calls (f(…), f:m(…))
• Skip for phase 1: generic for … in …, goto/labels, nested varargs ...
• Unit tests in lib/lua/tests/parse.sx: source → expected AST

Phase 2 — transpile: control flow + arithmetic

• lua-eval-ast entry
• Arithmetic (Lua 5.1 semantics — / is float)
• Comparison + logical (short-circuit, Lua truthy)
• .. concat with string/number coercion
• if, while, numeric for, local, assignment, blocks
• 30+ eval tests in lib/lua/tests/eval.sx

Phase 3 — tables + functions + first PUC-Rio slice

• function (anon, local, top-level), closures
• Multi-return: return as list, unpack at call sites
• Table constructors (array + hash + computed keys)
• Raw table access t.k / t[k] (no metatables yet)
• Vendor PUC-Rio 5.1.5 suite to lib/lua/lua-tests/ (just .lua files)
• lib/lua/conformance.sh + Python runner (model on lib/js/test262-runner.py)
• scoreboard.json + scoreboard.md baseline

Phase 4 — metatables + error handling (next run)

• Metatable dispatch: __index, __newindex, __add/__sub/…, __eq, __lt, __call, __tostring, __len
• pcall/xpcall/error via handler-bind
• Generic for … in …

Phase 5 — coroutines (the showcase)

• coroutine.create/.resume/.yield/.status/.wrap via perform/cek-resume

Phase 6 — standard library

• string — format, sub, find, match, gmatch, gsub, len, rep, upper, lower, byte, char
• math — full surface
• table — insert, remove, concat, sort, unpack
• io — minimal stub (read/write to SX IO surface)
• os — time/date subset

Phase 7 — modules + full conformance

• require / package via SX define-library/import
• Drive PUC-Rio scoreboard to 100%

Progress log

Newest first. Agent appends on every commit.

• 2026-04-24: lua: string lib — len/upper/lower/rep/sub (1-idx + neg)/byte/char/find/match/gmatch/gsub/format. Patterns are literal-only (no %d/etc.); format is %s/%d/%f/%% only. string.char uses printable-ASCII lookup + tab/nl/cr. 292 tests.
• 2026-04-24: lua: phase 5 — coroutines (create/resume/yield/status/wrap) via call/cc (perform/cek-resume not exposed to SX userland). Handles multi-yield + final return + arg passthrough. Fix: body's final return must jump via caller-k to the current resume's caller, not unwind through the stale first-call continuation. 273 tests.
• 2026-04-24: lua: generic for … in … — parser split (= → num, else in), new lua-for-in node, transpile to let-bound f,s,var + recursive __for_loop. Added ipairs/pairs/next/lua-arg globals. Lua fns now arity-tolerant (&rest __args + indexed bind) — needed because generic for always calls iter with 2 args. Noted early-return-in-nested-block as pre-existing limitation. 265 tests.
• 2026-04-24: lua: pcall/xpcall/error via SX guard + raise. Added lua-apply (arity-dispatch 0-8, apply fallback) because SX apply re-wraps raises as "Unhandled exception". Table payloads preserved (error({code = 42})). 256 total tests.
• 2026-04-24: lua: phase 4 — metatable dispatch (__index/__newindex/arith/compare/__call/__len), setmetatable/getmetatable/type globals, OO self:method pattern. Transpile routes all calls through lua-call (stashed sx-apply-ref to dodge user-shadowing of SX apply). Skipped __tostring (needs tostring() builtin). 247 total tests.
• 2026-04-24: lua: PUC-Rio scoreboard baseline — 0/16 runnable pass (0.0%). Top modes: 14× parse error, 1× print undef, 1× vararg transpile. Phase 3 complete.
• 2026-04-24: lua: conformance runner — conformance.sh shim + conformance.py (long-lived sx_server, epoch protocol, classify_error, writes scoreboard.{json,md}). 24 files classified in full run: 8 skip / 16 fail / 0 timeout.
• 2026-04-24: lua: vendored PUC-Rio 5.1 test suite (lua5.1-tests.tar.gz from lua.org) to lib/lua/lua-tests/ — 22 .lua files, 6304 lines; README kept for context.
• 2026-04-24: lua: raw table access — fix lua-set! to use dict-set! (mutating), fix lua-len has?→has-key?, #t works, mutation/chained/computed-key writes + reference semantics. 224 total tests.
• 2026-04-24: lua: phase 3 — table constructors verified (array, hash, computed keys, mixed, nested, dynamic values, fn values, sep variants). 205 total tests.
• 2026-04-24: lua: multi-return — lua-multi tagged value, lua-first/lua-nth-ret/lua-pack-return runtime, tail-position spread in return/local/assign. 185 total tests.
• 2026-04-24: lua: phase 3 — functions (anon/local/top-level) + closures verified (lexical capture, mutation-through-closure, recursion, HOFs). 175 total tests.
• 2026-04-24: lua: phase 2 transpile — arithmetic, comparison, short-circuit logical, .. concat, if/while/repeat/for-num/local/assign. 157 total tests green.
• 2026-04-24: lua: parser (exprs with precedence, all phase-1 statements, funcbody, table ctors, method/chained calls) — 112 total tokenizer+parser tests
• 2026-04-24: lua: tokenizer (numbers/strings/long-brackets/keywords/ops/comments) + 56 tests

Blockers

Shared-file issues that need someone else to fix. Minimal repro only.

• (none yet)

Known limitations (own code, not shared)

• string.find/match/gmatch/gsub patterns are LITERAL only — no %d/%a/./*/+/etc. Implementing Lua patterns is a separate work item; literal search covers the common case.
• string.format supports only %s, %d, %f, %%. No width/precision flags (%.2f, %5d).
• string.char supports printable ASCII 32–126 plus \t/\n/\r; other codes error.
• Early return inside nested block — if cond then return nil end ...rest doesn't exit the enclosing function; rest runs anyway. Use if cond then return X else return Y end instead. Likely needs guard+raise sentinel for proper fix.