Language versions

Version: 5

Every saved movement is pinned to the language version it was written against: an integer with a two-word name. The pin governs syntax and semantics, and every layer honours it: the parser, the checker, both engines, plugins and adapters. The version above is the current one, what a movement saved today is pinned to and what an entry point given no version compiles and runs under.

The table: LANGUAGE_VERSIONS, CURRENT_LANGUAGE_VERSION, SUPPORTED_LANGUAGE_VERSIONS and DEPRECATED_LANGUAGE_VERSIONS (packages/movement-lang/language_version.ts); the Rust side's is crates/movement-parser/src/version.rs. A test holds them equal to this document.
On the wire: the pin travels as languageVersion with a run's input, on segment.open (so an in-process adapter reads it from its segment), and on the checker's check.program. A remote adapter does not receive it: the adapter protocol carries no languageVersion today.

The versions #

version	name	supported	deprecated	is
1	Quiet Heron	no	no	the language as of tag v0.6.0
2	Bright Otter	no	no	the language from v0.7.0 through v0.9.1
3	Steady Lynx	no	no	the language from v0.10.0: a list literal is a tuple, exact at a literal index and a list of its members' union elsewhere
4	Luminous Owl	no	no	the language from v0.11.0: a match yields absent on a miss, a write handle reaches its pre-write record through `@old`
5	Dancing Wren	yes	no	the language after v0.11.0: no engine-side store and no meta edges; no `write … bind`, no `#` hops (a plugin is a function you call), `delete` only where the system declares a type deletable, `_resources` only on an extraction's result

The language release names the versions it supports; versions it has dropped are served by the platform's legacy packages until their saved movements are upgraded.

The integer is the identity: code compares it and never parses the name, which is display only. A version keeps its row after it leaves the supported set, so a movement pinned to it can still be refused by name. undefined is the migration guide from version 2 to 3, undefined from 3 to 4, and undefined from 4 to 5.

The rules #

Breaking changes never break a saved movement.

A break is a version conditional, never a fork. A spelling retired, a construct's meaning changed, a plugin's output reshaped, an engine rule tightened: each lands as a conditional (since(v, n) or before(v, n) on the compile or run context's languageVersion) at the point of difference in the parser, checker, engine, plugin or adapter. Never a forked parser, never a second engine.
The old behaviour is proved by its own corpus. Each older version's test corpus runs against the current code under that version. Adding a version adds its fixtures; removing one deletes its conditionals and its fixtures.
A changed meaning is diagnosed. Any construct whose meaning changed gets a checker diagnostic under the new version, so "validates clean under the new version" can never hide a silent behaviour change.
A release names what it supports and deprecates. Unsupported: validate and run refuse, loudly (MOV_LANGUAGE_VERSION_UNSUPPORTED, naming the version and the fix). Deprecated: it runs, with a warning (MOV_LANGUAGE_VERSION_DEPRECATED).
The pin moves only by an explicit upgrade. A person asks for it (lf upgrade, the API's or an agent's upgrade). Never automatically, and never by an ordinary edit. A movement that validates clean under a newer version is at most offered the upgrade (the deploy check reports it), never moved.
The CHANGELOG says why. The entry for a break names the version that introduces it and why.

Changes #

5, Dancing Wren (after v0.11.0): write … bind is retired (MOV_WRITE_BIND_RETIRED); every # hop is retired (MOV_META_HOP_RETIRED), a plugin being a function called by name; delete only of one stored record whose type's describe declares deletable: true (MOV_DELETE_NOT_DECLARED, MOV_DELETE_NOT_RECORD); _resources only on an extraction's result (MOV_RESOURCES_NOT_EXTRACTED), a system's record walking the edge its system declares to its files. Each is a checker refusal. On both engines _resources off an adapter's record is a MOVENG_UNSUPPORTED under 5 and the host's filesIn: "resources" envelope is not asked for one; an extraction's resources are unchanged on every version.
4, Luminous Owl (v0.11.0): a named match yields its handle or absent, and a miss no longer ends the scope (an unnamed match and link … { match … } are refused); created and committed are retired; -[:@old]-> off a write handle is the record the write found; write org { … } on a handle updates it in place; a handle reads the record as found for a field its write did not set; @ is reserved for artificial edges. Both engines run them (the Rust engine since PLAN-07A Task 4c, each change a since(v, 4) conditional where it differs).
3, Steady Lynx (v0.10.0): a list literal is a tuple. Exact at a literal index; a list of its members' union elsewhere.
2, Bright Otter (v0.7.0 through v0.9.1).
1, Quiet Heron: the language as of tag v0.6.0, the first pinned version.