# Common-Lisp-on-SX: conditions + restarts on delimited continuations

The headline showcase is the **condition system**. Restarts are *resumable* exceptions — every other Lisp implementation reinvents this on host-stack unwind tricks. On SX restarts are textbook delimited continuations: `signal` walks the handler chain; `invoke-restart` resumes the captured continuation at the restart point. Same delcc primitive that powers Erlang actors, expressed as a different surface.

End-state goal: ANSI Common Lisp subset with a working condition/restart system, CLOS multimethods (with `:before`/`:after`/`:around`), the LOOP macro, packages, and ~150 hand-written + classic programs.

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

- **Syntax:** ANSI Common Lisp surface. Read tables, dispatch macros (`#'`, `#(`, `#\`, `#:`, `#x`, `#b`, `#o`, ratios `1/3`).
- **Conformance:** ANSI X3.226 *as a target*, not bug-for-bug SBCL/CCL. "Reads like CL, runs like CL."
- **Test corpus:** custom + a curated slice of `ansi-test`. Plus classic programs: condition-system demo, restart-driven debugger, multiple-dispatch geometry, LOOP corpus.
- **Out of scope:** compilation to native, FFI, sockets, threads, MOP class redefinition, full pathname/logical-pathname machinery, structures with `:include` deep customization.
- **Packages:** simple — `defpackage`/`in-package`/`export`/`use-package`/`:cl`/`:cl-user`. No nicknames, no shadowing-import edge cases.

## Ground rules

- **Scope:** only touch `lib/common-lisp/**` and `plans/common-lisp-on-sx.md`. Don't edit `spec/`, `hosts/`, `shared/`, or any other `lib/<lang>/**`. CL primitives go in `lib/common-lisp/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

```
Common Lisp source
    │
    ▼
lib/common-lisp/reader.sx     — tokenizer + reader (read macros, dispatch chars)
    │
    ▼
lib/common-lisp/parser.sx     — AST: forms, declarations, lambda lists
    │
    ▼
lib/common-lisp/transpile.sx  — AST → SX AST (entry: cl-eval-ast)
    │
    ▼
lib/common-lisp/runtime.sx    — special forms, condition system, CLOS, packages, BIFs
```

Core mapping:
- **Symbol** = SX symbol with package prefix; package table is a flat dict.
- **Cons cell** = SX pair via `cons`/`car`/`cdr`; lists native.
- **Multiple values** = thread through `values`/`multiple-value-bind`; primary-value default for one-context callers.
- **Block / return-from** = captured continuation; `return-from name v` invokes the block-named `^k`.
- **Tagbody / go** = each tag is a continuation; `go tag` invokes it.
- **Unwind-protect** = scope frame with a cleanup thunk fired on any non-local exit.
- **Conditions / restarts** = layered handler chain on top of `handler-bind` + delcc. `signal` walks handlers; `invoke-restart` resumes a captured continuation.
- **CLOS** = generic functions are dispatch tables on argument-class lists; method combination computed lazily; `call-next-method` is a continuation.
- **Macros** = SX macros (sentinel-body) — defmacro lowers directly.

## Roadmap

### Phase 1 — reader + parser
- [x] Tokenizer: symbols (with package qualification `pkg:sym` / `pkg::sym`), numbers (int, float, ratio `1/3`, `#xFF`, `#b1010`, `#o17`), strings `"…"` with `\` escapes, characters `#\Space` `#\Newline` `#\a`, comments `;`, block comments `#| … |#`
- [x] Reader: list, dotted pair, quote `'`, function `#'`, quasiquote `` ` ``, unquote `,`, splice `,@`, vector `#(…)`, uninterned `#:foo`, nil/t literals
- [x] Parser: lambda lists with `&optional` `&rest` `&key` `&aux` `&allow-other-keys`, defaults, supplied-p variables
- [x] Unit tests in `lib/common-lisp/tests/read.sx`

### Phase 2 — sequential eval + special forms
- [x] `cl-eval-ast`: `quote`, `if`, `progn`, `let`, `let*`, `flet`, `labels`, `setq`, `setf` (subset), `function`, `lambda`, `the`, `locally`, `eval-when`
- [x] `block` + `return-from` via captured continuation
- [x] `tagbody` + `go` via per-tag continuations
- [x] `unwind-protect` cleanup frame
- [x] `multiple-value-bind`, `multiple-value-call`, `multiple-value-prog1`, `values`, `nth-value`
- [x] `defun`, `defparameter`, `defvar`, `defconstant`, `declaim`, `proclaim` (no-op)
- [x] Dynamic variables — `defvar`/`defparameter` produce specials; `let` rebinds via parameterize-style scope
- [x] 182 tests in `lib/common-lisp/tests/eval.sx`

### Phase 3 — conditions + restarts (THE SHOWCASE)
- [x] `define-condition` — class hierarchy rooted at `condition`/`error`/`warning`/`simple-error`/`simple-warning`/`type-error`/`arithmetic-error`/`division-by-zero`
- [x] `signal`, `error`, `cerror`, `warn` — all walk the handler chain
- [x] `handler-bind` — non-unwinding handlers, may decline by returning normally
- [x] `handler-case` — unwinding handlers (call/cc escape)
- [x] `restart-case`, `with-simple-restart`, `restart-bind`
- [x] `find-restart`, `invoke-restart`, `compute-restarts`
- [x] `with-condition-restarts` — associate restarts with a specific condition
- [x] `invoke-restart-interactively`, `*break-on-signals*`, `*debugger-hook*` (basic)
- [x] Classic programs in `lib/common-lisp/tests/programs/`:
  - [x] `restart-demo.sx` — division with `use-zero` and `retry` restarts (7 tests)
  - [x] `parse-recover.sx` — parser with skipped-token restart (6 tests)
  - [x] `interactive-debugger.sx` — policy-driven debugger hook, *debugger-hook* global (7 tests)
- [x] `lib/common-lisp/conformance.sh` + runner, `scoreboard.json` + `scoreboard.md` (363 total tests)

### Phase 4 — CLOS
- [x] `defclass` with `:initarg`/`:initform`/`:accessor`/`:reader`/`:writer`/`:allocation`
- [x] `make-instance`, `slot-value`, `(setf slot-value)`, `with-slots`, `with-accessors`
- [x] `defgeneric` with `:method-combination` (standard, plus `+`, `and`, `or`)
- [x] `defmethod` with `:before` / `:after` / `:around` qualifiers
- [x] `call-next-method` (continuation), `next-method-p`
- [x] `class-of`, `find-class`, `slot-boundp`, `change-class` (basic)
- [x] Multiple dispatch — method specificity by argument-class precedence list
- [x] Built-in classes registered for tagged values (`integer`, `float`, `string`, `symbol`, `cons`, `null`, `t`)
- [x] Classic programs:
  - [x] `geometry.sx` — `intersect` generic dispatching on (point line), (line line), (line plane) — 12 tests
  - [x] `mop-trace.sx` — `:before` + `:after` printing call trace — 13 tests

### Phase 5 — macros + LOOP + reader macros
- [x] `defmacro`, `macrolet`, `symbol-macrolet`, `macroexpand-1`, `macroexpand`
- [x] `gensym`, `gentemp`
- [ ] `set-macro-character`, `set-dispatch-macro-character`, `get-macro-character`
- [x] **The LOOP macro** — iteration drivers (`for … in/across/from/upto/downto/by`, `while`, `until`, `repeat`), accumulators (`collect`, `append`, `nconc`, `count`, `sum`, `maximize`, `minimize`), conditional clauses (`if`/`when`/`unless`/`else`), termination (`finally`/`thereis`/`always`/`never`), `named` blocks
- [x] LOOP test corpus: 27 tests covering all clause types

### Phase 6 — packages + stdlib drive
- [ ] `defpackage`, `in-package`, `export`, `use-package`, `import`, `find-package`
- [ ] Package qualification at the reader level — `cl:car`, `mypkg::internal`
- [ ] `:common-lisp` (`:cl`) and `:common-lisp-user` (`:cl-user`) packages
- [ ] Sequence functions — `mapcar`, `mapc`, `mapcan`, `reduce`, `find`, `find-if`, `position`, `count`, `every`, `some`, `notany`, `notevery`, `remove`, `remove-if`, `subst`
- [ ] List ops — `assoc`, `getf`, `nth`, `last`, `butlast`, `nthcdr`, `tailp`, `ldiff`
- [ ] String ops — `string=`, `string-upcase`, `string-downcase`, `subseq`, `concatenate`
- [ ] FORMAT — basic directives `~A`, `~S`, `~D`, `~F`, `~%`, `~&`, `~T`, `~{...~}` (iteration), `~[...~]` (conditional), `~^` (escape), `~P` (plural)
- [ ] Drive corpus to 200+ green

## SX primitive baseline

Use vectors for arrays; numeric tower + rationals for numbers; ADTs for tagged data;
coroutines for fibers; string-buffer for mutable string building; bitwise ops for bit
manipulation; multiple values for multi-return; promises for lazy evaluation; hash tables
for mutable associative storage; sets for O(1) membership; sequence protocol for
polymorphic iteration; gensym for unique symbols; char type for characters; string ports
+ read/write for reader protocols; regexp for pattern matching; bytevectors for binary
data; format for string templating.

## Progress log

_Newest first._

- 2026-05-05: Phase 4 CLOS fully complete — `lib/common-lisp/clos.sx` (27 forms): clos-class-registry (8 built-in classes), defclass/make-instance/slot-value/slot-boundp/set-slot-value!/find-class/change-class, defgeneric/defmethod with :before/:after/:around, clos-call-generic (standard method combination: sort by specificity, fire befores, call primary chain, fire afters in reverse), call-next-method/next-method-p, with-slots, accessor installation; 41 tests in `tests/clos.sx`; classic programs `geometry.sx` (12 tests, multi-dispatch intersect on P/L/Plane) and `mop-trace.sx` (13 tests, :before/:after tracing). Dynamic variables in eval.sx: cl-apply-dyn saves/restores global bindings around let for specials (cl-mark-special!/cl-special?/cl-dyn-unbound). Key gotchas: qualifier strings are "before"/"after"/"around" (no colon); dict-set pure = assoc; dict->list = (map (fn (k) (list k (get d k))) (keys d)); clos-add-reader-method bootstrapped via set! after defmethod defined; test isolation: use unique var names to avoid *y* collision. 437 total tests, 0 failed.
- 2026-05-05: Phase 3 fully complete — conformance.sh runner + scoreboard.json/scoreboard.md; 363 total tests across all suites (79 reader, 31 parser, 174 eval, 59 conditions, 7+6+7 classic programs).
- 2026-05-05: Phase 3 complete — cl-debugger-hook/cl-invoke-debugger in runtime.sx (cl-error routes through hook), cl-break-on-signals (fires hook before handlers on type match), cl-invoke-restart-interactively (calls fn with no args); 4 new tests (147 total). Phase 3 all boxes ticked.
- 2026-05-05: Phase 3 interactive-debugger.sx — cl-debugger-hook global, cl-invoke-debugger, cl-error-with-debugger, make-policy-debugger; 7 tests (143 total). Tests wired into test.sh program suite runner. Phase 3 condition core complete.
- 2026-05-05: Phase 3 classic programs — `tests/programs/restart-demo.sx` (7 tests: safe-divide with use-zero + retry restarts) and `tests/programs/parse-recover.sx` (6 tests: token parser with skip-token + use-zero restarts, handler-case abort). Key gotcha: use `=` not `equal?` for list comparison in sx_server.
- 2026-05-05: Phase 3 conditions + restarts — `cl-condition-classes` hierarchy (15 types), `cl-condition?`/`cl-condition-of-type?`, `cl-make-condition`, `cl-define-condition`, `cl-signal`/`cl-error`/`cl-warn`/`cl-cerror`, `cl-handler-bind` (non-unwinding), `cl-handler-case` (call/cc escape), `cl-restart-case`/`cl-with-simple-restart`, `cl-find-restart`/`cl-invoke-restart`/`cl-compute-restarts`, `cl-with-condition-restarts`; 55 new tests in `tests/conditions.sx` (123 total runtime tests). Key gotcha: `cl-condition-classes` must be captured at define-time via `let` in `cl-condition-of-type?` — free-variable lookup at call-time fails through env_merge parent chain.
- 2026-05-05: multiple values — VALUES returns {:cl-type "mv"} wrapper for 2+ values; cl-mv-primary/cl-mv-vals helpers; MULTIPLE-VALUE-BIND binds vars to value list; MULTIPLE-VALUE-CALL/PROG1/NTH-VALUE; cl-mv-primary applied in IF/AND/OR/COND/cl-call-fn for single-value contexts; 15 new tests (174 eval, 346 total green).
- 2026-05-05: unwind-protect — cl-eval-unwind-protect: eval protected form, run cleanup with for-each (discards results, preserves original sentinel), return original result; 8 new tests (159 eval, 331 total green).
- 2026-05-05: tagbody + go — cl-go-tag? sentinel; cl-eval-tagbody runs body with tag-index map (keys str-normalised for integer tags); go-tag propagation in cl-eval-body alongside block-return; 11 new tests (151 eval, 323 total green).
- 2026-05-05: block + return-from — sentinel propagation in cl-eval-body; cl-eval-block catches matching sentinels; BLOCK/RETURN-FROM/RETURN dispatch in cl-eval-list; 13 new tests (140 eval, 312 total green). Parser: CL strings → {:cl-type "string"} dicts.
- 2026-04-25: Phase 2 eval — 127 tests, 299 total green. `lib/common-lisp/eval.sx`: cl-eval-ast with quote/if/progn/let/let*/flet/labels/setq/setf/function/lambda/the/locally/eval-when; defun/defvar/defparameter/defconstant; built-in arithmetic (+/-/*//, min/max/abs/evenp/oddp), comparisons, predicates, list ops (car/cdr/cons/list/append/reverse/length/nth/first/second/third/rest), string ops, funcall/apply/mapcar. Key gotchas: SX reduce is (reduce fn init list) not (reduce fn list init); CL true literal is t not true; builtins registered in cl-global-env.fns via wrapper dicts for #' syntax.
- 2026-04-25: Phase 1 lambda-list parser — 31 new tests, 172 total green. `cl-parse-lambda-list` in `parser.sx` + `tests/lambda.sx`. Handles &optional/&rest/&body/&key/&aux/&allow-other-keys, defaults, supplied-p. Key gotchas: `(when (> (len items) 0) ...)` not `(when items ...)` (empty list is truthy); custom `cl-deep=` needed for dict/list structural equality in tests.
- 2026-04-25: Phase 1 reader/parser — 62 new tests, 141 total green. `lib/common-lisp/parser.sx`: cl-read/cl-read-all, lists, dotted pairs, quote/backquote/unquote/splice/#', vectors, #:uninterned, NIL→nil, T→true, reader macro wrappers.
- 2026-04-25: Phase 1 tokenizer — 79 tests green. `lib/common-lisp/reader.sx` + `tests/read.sx` + `test.sh`. Handles symbols (pkg:sym, pkg::sym), integers, floats, ratios, hex/binary/octal, strings, #\ chars, reader macros (#' #( #: ,@), line/block comments. Key gotcha: SX `str` for string concat (not `concat`), substring-based read-while.

## Blockers

- _(none yet)_