Tya v0.33 Specification — Canonical Syntax, Step 1

Tya v0.33 begins the multi-version push toward Canonical Syntax, the property defined in docs/CANONICAL_SYNTAX.md: every well-formed Tya program has exactly one source representation, and the formatter (tya format) is the canonical serializer.

The full Canonical Syntax landing requires changes to the parser, the AST, the formatter, and the entire normalized codebase. v0.33 is the first step of that landing. It is intentionally additive and non-breaking so the rest of the work can land in subsequent minor releases without disturbing existing programs.

Goals (v0.33)

Parser accepts the parenthesized multi-parameter lambda form (a, b) -> body (docs/CANONICAL_SYNTAX.md §5.3.4).
The existing comma-separated form a, b -> body and the single-parameter form name -> body remain valid; this release is purely additive.
The full Canonical Syntax direction is referenced from this SPEC and from ROADMAP.md so the path through v0.34–v0.37 is visible.

Non-Goals (v0.33)

Comment AST attributes (leading_comments, line_end_comment, file_header_comments) — deferred to v0.34.
Parser rejection of else if, single-line trailing commas, and forbidden comment positions — deferred to v0.34.
Formatter wrap rules per construct — deferred to v0.35–v0.36.
Triple-quoted string rewrite rule — deferred to v0.36.
Codebase-wide normalization and turning non-canonical forms into parse errors — deferred to v0.37.

Surface Syntax

ParenFunc = '(' Ident { ',' Ident } ')' '->' FuncBody

Examples:

add = (a, b) -> a + b

square = (x) -> x * x

triple = (a, b, c) ->
  return a + b + c

The body grammar is identical to today’s name -> body form: an inline expression after ->, or a block body when -> is followed by a newline + INDENT.

Disambiguation

(expr) (a parenthesized expression) and (a, b) -> body (a parenthesized parameter list) are disambiguated by lookahead. The parser commits to the parameter-list form only when it sees:

LPAREN IDENT (',' IDENT)* RPAREN ARROW

In every other case ( opens a grouping expression. The empty form () -> body continues to work as before.

Acceptance Criteria

A v0.33 build is acceptable when:

add = (a, b) -> a + b parses, type-checks, and runs to produce add(2, 3) == 5.
(x) -> x * x parses and runs.
(a, b, c) -> followed by an indented block body parses and runs.
The pre-existing forms a, b -> body, a -> body, () -> body, and -> body continue to work unchanged.
go test ./... -count=1 passes, including the self-host invariant.

Multi-Version Plan

Version	Canonical Syntax progress
v0.33	Parenthesized multi-parameter lambda (this release).
v0.34	Add `leading_comments` / `line_end_comment` / `file_header_comments` to AST nodes. Parser attaches comments per `docs/CANONICAL_SYNTAX.md` §3. Reject `else if`. Reject single-line trailing commas in `[]`/`()`/`{}`. Reject forbidden comment positions (§3.4).
v0.35	Formatter v1: operator spacing (§7), blank-line rules (§3.5), single-line forms only, empty `else` removal (§8.7), import sorting and grouping (§8.4), empty-collection normalization (§8.6).
v0.36	Formatter v2: per-construct multi-line wrap (§5), 80-column limit, atomic-token exception, `"""..."""` rewrite (§6.3), idempotency.
v0.37	Normalize `stdlib/`, `examples/`, `selfhost/`, `tests/testdata/` with the formatter. Verify self-host fixed point. Reject non-canonical forms at parse time once the codebase is fully normalized.

docs/CANONICAL_SYNTAX.md remains the single source of truth for the target shape. Each minor release’s SPEC document references it.

Self-Host Invariant

The self-host pipeline does not use the (a, b) -> body form. Its source remains valid v0.33 source. TestSelfhostV01Scripts continues to pass.

Testing Strategy

Parser unit tests for (a, b) -> body, (x) -> body, (a, b, c) ->\n block, mixed with the existing forms.
CLI script test (tests/testdata/v33/paren_lambda.txtar) for an end-to-end tya run.
Self-host fixed point (TestSelfhostV01Scripts) continues to pass.
Default test suite (go test ./...) remains green.