# CHECKPOINT-LANG — user-facing language features

Companion to [PLAN-LANG.md](PLAN-LANG.md). Update after every step (one step at
a time, per the cadence rule).

## Last completed step
**Tuple syntax cutover — `Tuple(...)` type + `.(...)` value (commit 989e18b7).**
The bare-paren tuple grammar was replaced with explicit, position-unambiguous
forms that mirror how structs work:

- type     `(A, B)`         → `Tuple(A, B)`         (named keeps `:` — `Tuple(x: A, y: B)`)
- value    `(a, b)`         → `.(a, b)`             (named uses `=` — `.(x = a, y = b)`)
- typed    (new)            → `Tuple(A, B).(a, b)`  (like `Point.{...}`)
- failable `-> (T, !)`      → `-> T !`
           `-> (T1, T2, !)` → `-> Tuple(T1, T2) !`  (error channel OUTSIDE the Tuple)

Bare `(...)` is now grouping ONLY, everywhere; a comma in bare parens is a hard
error with a migration hint. Grouping, function types `(A, B) -> R`, param lists,
lambdas, match bindings, and `?(?T)` grouping are unaffected. `Tuple(...)` is
strictly a TYPE in every position (incl. `size_of` / `type_info` args); a tuple
VALUE comes only from `.(...)` or `Tuple(...).(...)`. A bare `Tuple(1, 2)`
(non-type elements) is rejected. Field access is unchanged (`.0`/`.1` positional,
`.x` named). Optional semantics are untouched — `??T ≡ ?T` was NOT done; nested
optionals (`?(?i64)`) stay genuine.

The ~110 tuple-bearing corpus files were migrated by a one-shot AST-aware
migrator; new examples landed (0130 new syntax, 0131 typed construction, 1060
named-tuple failable return). Issue **0189** filed (non-type expression in type
position silently fabricates an empty struct — surfaced while validating the
`Tuple(i32, g.a)` rejection path).

Docs updated to the new syntax: `specs.md` (Tuple Types section, function
multi-return note, all error-channel sections, Variadic Heterogeneous Type Packs,
Tuple UFCS Splatting, and the normative Grammar block) and `readme.md` (inline-asm
named-tuple return + the `N → a tuple` rule). Stale old-syntax mentions in example
header comments were corrected (comments only — no code touched). Suite green
(810 ran, 0 failed).

## Current state
Tuple syntax cutover shipped and documented. `Tuple(...)` / `.(...)` are the only
tuple spellings across the corpus, specs, and readme.

## Next step
Pick up the next incomplete LANG step from [PLAN-LANG.md](PLAN-LANG.md).

## Log
- **Tuple syntax cutover** (commit 989e18b7): `(A,B)`/`(a,b)` tuples replaced by
  `Tuple(A,B)` type + `.(a,b)` value; failable `!` moved outside the Tuple
  (`-> T !` / `-> Tuple(...) !`); bare parens are grouping-only. Docs (specs.md +
  readme.md) and stale example-comment mentions migrated to the new syntax. Issue
  0189 filed. Suite green (810 ran, 0 failed).