Phase 9. Agents (final class, synchronous)

Field	Value
MEP	MEP-49 §Phases · Phase 9
Status	LANDED
Started	2026-05-28 13:40 (GMT+7)
Landed	2026-05-28 13:40 (GMT+7)
Tracking issue	—
Tracking PR	—

Gate

TestPhase9Agents: 10 fixtures green on Swift 6.0+, macOS 15. Gate builds each fixture and compares stdout to .expected.

Goal-alignment audit

Mochi agents encapsulate mutable state with a set of named operations (intents). For the v1 Swift backend the lowering target is public final class: each field becomes a public var property, each intent becomes a public func method. This is simpler than an actor-based mailbox pattern, avoids async colouring until Phase 11, and maps cleanly onto the synchronous fixture suite inherited from other backends. The actor+AsyncStream mailbox pattern is deferred to a future sub-MEP.

Sub-phases

#	Scope	Status	Commit
9.0	AgentDecl → public final class; fields → public var; intents → public func	LANDED	mep/0049-phase-09
9.1	AgentLit → ClassName(field1: val1, ...) initialiser call	LANDED	mep/0049-phase-09
9.2	AgentIntentCallExpr → receiver.method(args...)	LANDED	mep/0049-phase-09
9.3	Rewrite __self->fieldName refs in intent bodies to bare fieldName	LANDED	mep/0049-phase-09
9.4	actor + AsyncStream<Message> mailbox; OTP-style supervision	DEFERRED	—
9.5	@ui annotation → @MainActor isolation	DEFERRED	—

Sub-phase 9.0 -- Final class declaration

Decisions made (9.0)

public final class: a Mochi agent Counter { var n: int = 0; ... } lowers to:

public final class Counter {
    public var n: Int64

    public init(n: Int64 = Int64(0)) {
        self.n = n
    }

    public func inc() {
        n = (n + Int64(1))
    }

    public func value() -> Int64 {
        return n
    }
}

Why final class instead of actor: the v1 gate fixtures are synchronous (no cross-agent calls, no concurrent access). Using final class avoids async/await requirements at every call site and keeps the generated code readable. The actor-based pattern is preserved as future work in 9.4.

Field types: each aotir.AgentDecl.Field is lowered to a Swift type via the same lowerFieldTypeName helper used for records.

Init signature: the generated public init takes one parameter per field. Default values are not yet emitted (fields with literal initialisers in the Mochi source do not yet propagate defaults to the Swift init).

Sub-phase 9.1 -- Agent literal

Decisions made (9.1)

AgentLit → labeled call: Counter { n: 0 } in Mochi → Counter(n: Int64(0)) in Swift via RawSwiftExpr with labeled argument list.

Sub-phase 9.2 -- Intent call

Decisions made (9.2)

AgentIntentCallExpr: counter.inc() and counter.value() in Mochi lower to identical receiver.method(args...) calls in Swift. The lowerer emits a MethodCallExpr node.

SpawnedRef: the SpawnedRef flag (used for Erlang actor spawning in the BEAM backend) is not supported in the Swift backend and returns an error if encountered.

Sub-phase 9.3 -- Self reference rewriting

Decisions made (9.3)

__self->fieldName pattern: the aotir IR encodes field accesses inside intent bodies as __self->fieldName (C-style, matching the C backend convention). Swift class methods access self.field implicitly, so the lowerer runs rewriteAgentSelfRefs before lowering the intent body. This pass walks the aotir block and replaces every VarExpr whose name matches __self->X with just X.

Files changed

File	Purpose
transpiler3/swift/lower/lower.go	lowerAgentDecl, lowerAgentLit, lowerAgentIntentCallExpr, rewriteAgentSelfRefs
transpiler3/swift/sxtree/nodes.go	ClassDecl, ClassProp node types
transpiler3/swift/build/phase09_test.go	TestPhase9Agents: 10 fixtures
tests/transpiler3/swift/fixtures/phase09-agents/	10 fixture directories

Test set

• TestPhase9Agents -- 10 fixtures: agent_bool, agent_chain, agent_cond, agent_counter, agent_float, agent_multi, agent_nested_call, agent_params, agent_string, agent_two.

Deferred work

• actor + AsyncStream<Message> mailbox pattern (request-reply via withCheckedContinuation, fire-and-forget via nonisolated continuation). Deferred to Phase 9.4.
• OTP-style supervision (MochiRuntime.Supervisor actor, restart strategies). Deferred to Phase 9.4.
• @ui annotation → @MainActor-isolated class conforming to ObservableObject. Deferred to Phase 9.5.
• Distributed actors (Swift Distributed Actors framework). Deferred.