Tya v0.37 Specification — Canonical Syntax, Step 5

Tya v0.37 introduces the AST-driven canonical serializer (unparse) that Canonical Syntax §11.3 requires. v0.37 ships the foundation: formatter.Unparse(prog *ast.Program) (string, error) that handles a useful subset of the AST. v0.38 extends coverage and adds the wrap rules; v0.39 wires the serializer into the user-facing tya format command and normalizes the codebase.

v0.37 does not change tya fmt behavior. The existing v0.2 text formatter continues to ship. The serializer is exported for tests and opt-in tooling.

Goals (v0.37)

• New internal/formatter.Unparse(prog) (string, error) that renders prog as canonical Tya source for the supported subset.
• Coverage of the common case of Tya programs: imports, simple assignments (with all literal / operator / call / member / index / array / dict expressions), expression statements, returns, raises, break / continue, single-line and block-bodied lambdas, if / elseif / else, while, for.
• Operator spacing, single-line forms, and indentation per CANONICAL §4 / §7.
• if … elseif … is emitted using the canonical elseif keyword even when the source spelled it as nested else / if.

Non-Goals (v0.37)

• Module / class / interface declarations — Unparse returns an unsupported error for these. v0.38 covers them.
• match / try / raise (raise is supported; match and try/catch are deferred).
• Multi-line wrap forms (CANONICAL §5). All output is single-line per construct in v0.37.
• 80-column limit and atomic-token exception.
• """...""" rewrite rule (CANONICAL §6.3).
• Comment emission. Unparse does not yet read Program.HeaderComments or Program.Comments. v0.38 wires those in.
• Empty-else removal, import sort, blank-line rules. Deferred.
• Replacing tya fmt with the AST-driven serializer.
• Idempotency or full round-trip guarantees outside the supported subset.

API

package formatter

// Unparse renders prog as canonical Tya source. Returns an error
// when the AST contains a node v0.37 does not yet handle. The
// existing FormatSource(string) text pass is unchanged.
func Unparse(prog *ast.Program) (string, error)

The error is a sentinel-style fmt.Errorf("formatter.Unparse: …"). Callers (tests, tooling) decide whether to fall back to the text formatter or surface the error.

Acceptance Criteria

A v0.37 build is acceptable when:

1. formatter.Unparse round-trips programs in the supported subset to canonical source: assignments, imports, expression statements, returns / raises / break / continue, if / elseif / else, while, for, single-line and block-bodied name -> body and (a, b) -> body lambdas, all literal / operator / call / member / index / array / dict expressions.
2. Unparse returns an unsupported error when the AST contains a module / class / interface / match / try node.
3. The default tya fmt and tya format continue to use the v0.2 text pass; no behavior change for existing CLI users.
4. go test ./... -count=1 passes, including the self-host invariant.

Multi-Version Plan (updated)

Self-Host Invariant

Unparse is not on the self-host path. The v0.2 text formatter remains the only user-facing serializer. TestSelfhostV01Scripts continues to pass.