hakorune/docs/archive/phases/phase-12.7/ancp-specs/ANCP-Reversible-Mapping-v1.md

ANCP v1 – Reversible Mapping (P0 subset)

Status: Preview (12.7‑C P0). Scope is the sugar subset already implemented and gated in 12.7‑B.

Goals

• Provide a clear, reversible mapping between Nyash sugar and canonical forms.
• Make round‑trip (original → canonical → ANCP → canonical → original) predictable for the subset.

Gating

• Runtime sugar is gated by NYASH_SYNTAX_SUGAR_LEVEL=basic|full.
• ANCP tools/nyfmt remain PoC/docs only at this stage.

Subset Mappings

• Pipeline |>

  • Nyash: lhs |> f(a,b) → Canonical: f(lhs, a, b)
  • Nyash: lhs |> obj.m(a) → Canonical: obj.m(lhs, a)
  • Round‑trip invariant: No change of call order or arity.

• Safe Access ?.

  • Nyash: a?.b → Canonical (peek): peek a { null => null, else => a.b }
  • Nyash: a?.m(x) → Canonical: peek a { null => null, else => a.m(x) }
  • Round‑trip invariant: No change of receivers/args; only the null guard appears.

• Default ??

  • Nyash: a ?? b → Canonical (peek): peek a { null => b, else => a }
  • Round‑trip invariant: Both branches preserved as‑is.

• Range ..

  • Nyash: a .. b → Canonical: Range(a, b)
  • Round‑trip invariant: Closed form preserved; no inclusive/exclusive change.

• Compound Assign +=, -=, *=, /=

  • Nyash: x += y → Canonical: x = x + y（x は変数/フィールド）
  • Round‑trip invariant: Operator identity preserved; left target identical.

Examples (Before / Canonical / Round‑Trip)

1. Pipeline + Default

Before:     data |> normalize() |> transform() ?? fallback
Canonical:  peek transform(normalize(data)) { null => fallback, else => transform(normalize(data)) }
RoundTrip:  data |> normalize() |> transform() ?? fallback

2. Safe Access Chain

Before:     user?.profile?.name
Canonical:  peek user { null => null, else => peek user.profile { null => null, else => user.profile.name } }
RoundTrip:  user?.profile?.name

3. Range + Compound Assign

Before:     i += 1; r = 1 .. 5
Canonical:  i = i + 1; r = Range(1, 5)
RoundTrip:  i += 1; r = 1 .. 5

Notes

• Precise precedence handling is left to the parser; mappings assume already parsed trees.
• Full ANCP compact tokens will be documented in a separate spec revision.