# Ruby-on-SX: fibers + blocks + open classes on delimited continuations

The headline showcase is **fibers** — Ruby's `Fiber.new { … Fiber.yield v … }` / `Fiber.resume` are textbook delimited continuations with sugar. MRI implements them by swapping C stacks; on SX they fall out of the existing `perform`/`cek-resume` machinery for free. Plus blocks/yield (lexical escape continuations, same shape as Smalltalk's non-local return), method_missing, and singleton classes.

End-state goal: Ruby 2.7-flavoured subset, Enumerable mixin, fibers + threads-via-fibers (no real OS threads), method_missing-driven DSLs, ~150 hand-written + classic programs.

## Scope decisions (defaults — override by editing before we spawn)

- **Syntax:** Ruby 2.7. No 3.x pattern matching, no rightward assignment, no endless methods. We pick 2.7 because it's the biggest semantic surface that still parses cleanly.
- **Conformance:** "Reads like Ruby, runs like Ruby." Slice of RubySpec (Core + Library subset), not full RubySpec.
- **Test corpus:** custom + curated RubySpec slice. Plus classic programs: fiber-based generator, internal DSL with method_missing, mixin-based Enumerable on a custom class.
- **Out of scope:** real threads, GIL, refinements, `binding_of_caller` from non-Ruby contexts, Encoding object beyond UTF-8/ASCII-8BIT, RubyVM::* introspection beyond bytecode-disassembly placeholder, IO subsystem beyond `puts`/`gets`/`File.read`.
- **Symbols:** SX symbols. Strings are mutable copies; symbols are interned.

## Ground rules

- **Scope:** only touch `lib/ruby/**` and `plans/ruby-on-sx.md`. Don't edit `spec/`, `hosts/`, `shared/`, or any other `lib/<lang>/**`. Ruby primitives go in `lib/ruby/runtime.sx`.
- **SX files:** use `sx-tree` MCP tools only.
- **Commits:** one feature per commit. Keep `## Progress log` updated and tick roadmap boxes.

## Architecture sketch

```
Ruby source
    │
    ▼
lib/ruby/tokenizer.sx   — keywords, ops, %w[], %i[], heredocs (deferred), regex (deferred)
    │
    ▼
lib/ruby/parser.sx      — AST: classes, modules, methods, blocks, calls
    │
    ▼
lib/ruby/transpile.sx   — AST → SX AST (entry: rb-eval-ast)
    │
    ▼
lib/ruby/runtime.sx     — class table, MOP, dispatch, fibers, primitives
```

Core mapping:
- **Object** = SX dict `{:class :ivars :singleton-class?}`. Instance variables live in `ivars` keyed by symbol.
- **Class** = SX dict `{:name :superclass :methods :class-methods :metaclass :includes :prepends}`. Class table is flat.
- **Method dispatch** = lookup walks ancestor chain (prepended → class → included modules → superclass → …). Falls back to `method_missing` with a `Symbol`+args.
- **Block** = lambda + escape continuation. `yield` invokes the block in current context. `return` from within a block invokes the enclosing-method's escape continuation.
- **Proc** = lambda without strict arity. `Proc.new` + `proc {}`.
- **Lambda** = lambda with strict arity + `return`-returns-from-lambda semantics.
- **Fiber** = pair of continuations (resume-k, yield-k) wrapped in a record. `Fiber.new { … }` builds it; `Fiber.resume` invokes the resume-k; `Fiber.yield` invokes the yield-k. Built directly on `perform`/`cek-resume`.
- **Module** = class without instance allocation. `include` puts it in the chain; `prepend` puts it earlier; `extend` puts it on the singleton.
- **Singleton class** = lazily allocated per-object class for `def obj.foo` definitions.
- **Symbol** = interned SX symbol. `:foo` reads as `(quote foo)` flavour.

## Roadmap

### Phase 1 — tokenizer + parser
- [ ] Tokenizer: keywords (`def end class module if unless while until do return yield begin rescue ensure case when then else elsif`), identifiers (lowercase = local/method, `@` = ivar, `@@` = cvar, `$` = global, uppercase = constant), numbers (int, float, `0x` `0o` `0b`, `_` separators), strings (`"…"` interpolation, `'…'` literal, `%w[a b c]`, `%i[a b c]`), symbols `:foo` `:"…"`, operators (`+ - * / % ** == != < > <= >= <=> === =~ !~ << >> & | ^ ~ ! && || and or not`), `:: . , ; ( ) [ ] { } -> => |`, comments `#`
- [ ] Parser: program is sequence of statements separated by newlines or `;`; method def `def name(args) … end`; class `class Foo < Bar … end`; module `module M … end`; block `do |a, b| … end` and `{ |a, b| … }`; call sugar (no parens), `obj.method`, `Mod::Const`; arg shapes (positional, default, splat `*args`, double-splat `**opts`, block `&blk`)
- [ ] If/while/case expressions (return values), `unless`/`until`, postfix modifiers
- [ ] Begin/rescue/ensure/retry, raise, raise with class+message
- [ ] Unit tests in `lib/ruby/tests/parse.sx`

### Phase 2 — object model + sequential eval
- [ ] Class table bootstrap: `BasicObject`, `Object`, `Kernel`, `Module`, `Class`, `Numeric`, `Integer`, `Float`, `String`, `Symbol`, `Array`, `Hash`, `Range`, `NilClass`, `TrueClass`, `FalseClass`, `Proc`, `Method`
- [ ] `rb-eval-ast`: literals, variables (local, ivar, cvar, gvar, constant), assignment (single and parallel `a, b = 1, 2`, splat receive), method call, message dispatch
- [ ] Method lookup walks ancestor chain; cache hit-class per `(class, selector)`
- [ ] `method_missing` fallback constructing args list
- [ ] `super` and `super(args)` — lookup in defining class's superclass
- [ ] Singleton class allocation on first `def obj.foo` or `class << obj`
- [ ] `nil`, `true`, `false` are singletons of their classes; tagged values aren't boxed
- [ ] Constant lookup (lexical-then-inheritance) with `Module.nesting`
- [ ] 60+ tests in `lib/ruby/tests/eval.sx`

### Phase 3 — blocks + procs + lambdas
- [ ] Method invocation captures escape continuation `^k` for `return`; binds it as block's escape
- [ ] `yield` invokes implicit block
- [ ] `block_given?`, `&blk` parameter, `&proc` arg unpacking
- [ ] `Proc.new`, `proc { }`, `lambda { }` (or `->(x) { x }`)
- [ ] Lambda strict arity + lambda-local `return` semantics
- [ ] Proc lax arity (`a, b, c` unpacks Array; missing args nil)
- [ ] `break`, `next`, `redo` — `break` is escape-from-loop-or-block; `next` is escape-from-block-iteration; `redo` re-runs current iteration
- [ ] 30+ tests in `lib/ruby/tests/blocks.sx`

### Phase 4 — fibers (THE SHOWCASE)
- [ ] `Fiber.new { |arg| … Fiber.yield v … }` allocates a fiber record with paired continuations
- [ ] `Fiber.resume(args…)` resumes the fiber, returning the value passed to `Fiber.yield`
- [ ] `Fiber.yield(v)` from inside the fiber suspends and returns control to the resumer
- [ ] `Fiber.current` from inside the fiber
- [ ] `Fiber#alive?`, `Fiber#raise` (deferred)
- [ ] `Fiber.transfer` — symmetric coroutines (resume from any side)
- [ ] Classic programs in `lib/ruby/tests/programs/`:
  - [ ] `generator.rb` — pull-style infinite enumerator built on fibers
  - [ ] `producer-consumer.rb` — bounded buffer with `Fiber.transfer`
  - [ ] `tree-walk.rb` — recursive tree walker that yields each node, driven by `Fiber.resume`
- [ ] `lib/ruby/conformance.sh` + runner, `scoreboard.json` + `scoreboard.md`

### Phase 5 — modules + mixins + metaprogramming
- [ ] `include M` — appends M's methods after class methods in chain
- [ ] `prepend M` — prepends M before class methods
- [ ] `extend M` — adds M to singleton class
- [ ] `Module#ancestors`, `Module#included_modules`
- [ ] `define_method`, `class_eval`, `instance_eval`, `module_eval`
- [ ] `respond_to?`, `respond_to_missing?`, `method_missing`
- [ ] `Object#send`, `Object#public_send`, `Object#__send__`
- [ ] `Module#method_added`, `singleton_method_added` hooks
- [ ] Hooks: `included`, `extended`, `inherited`, `prepended`
- [ ] Internal-DSL classic program: `lib/ruby/tests/programs/dsl.rb`

### Phase 6 — stdlib drive
- [ ] `Enumerable` mixin: `each` (abstract), `map`, `select`/`filter`, `reject`, `reduce`/`inject`, `each_with_index`, `each_with_object`, `take`, `drop`, `take_while`, `drop_while`, `find`/`detect`, `find_index`, `any?`, `all?`, `none?`, `one?`, `count`, `min`, `max`, `min_by`, `max_by`, `sort`, `sort_by`, `group_by`, `partition`, `chunk`, `each_cons`, `each_slice`, `flat_map`, `lazy`
- [ ] `Comparable` mixin: `<=>`, `<`, `<=`, `>`, `>=`, `==`, `between?`, `clamp`
- [ ] `Array`: indexing, slicing, `push`/`pop`/`shift`/`unshift`, `concat`, `flatten`, `compact`, `uniq`, `sort`, `reverse`, `zip`, `dig`, `pack`/`unpack` (deferred)
- [ ] `Hash`: `[]`, `[]=`, `delete`, `merge`, `each_pair`, `keys`, `values`, `to_a`, `dig`, `fetch`, default values, default proc
- [ ] `Range`: `each`, `step`, `cover?`, `include?`, `size`, `min`, `max`
- [ ] `String`: indexing, slicing, `split`, `gsub` (string-arg version, regex deferred), `sub`, `upcase`, `downcase`, `strip`, `chomp`, `chars`, `bytes`, `to_i`, `to_f`, `to_sym`, `*`, `+`, `<<`, format with `%`
- [ ] `Integer`: `times`, `upto`, `downto`, `step`, `digits`, `gcd`, `lcm`
- [ ] Drive corpus to 200+ green

## Progress log

_Newest first._

- _(none yet)_

## Blockers

- _(none yet)_