Spec Update: Batch 10 — Concurrency: Tasks and Async

Date: 2026-04-16 Plans Referenced: Plan 121 (Task/Msg system), Plan 124 (Async/Await), Plan 126 (Micro-concurrency) Source Files: ast/task.rs (TaskDef, TaskOnBlock, TaskMsgPattern, TaskAttr, LiteralValue), ast.rs (AsyncBlock, Await, Go expr variants), token.rs (Task, Spawn, Await, Reply, Go keywords) Sections Updated: Concurrency: Tasks and Async (Section 17 — NEW)

Old Content

No concurrency documentation existed.

New Content

Task Definition

• task Name { state, start(), on { handlers }, stop() }
• State fields with mutability and initial values
• Lifecycle hooks: start(), stop()
• Message handlers with pattern matching

Task Attributes

• #[single] for singleton tasks

Message Patterns (4 types)

• Simple: Reset (no data)
• With bindings: Add(val) (named bindings)
• Literal match: "start" (exact value)
• Type binding: msg str (capture by type)

Spawning and Communication

• spawn TaskName() → Handle<T>
• handle.send(Message)
• reply value for ask/reply RPC

Async/Await (Plan 124)

• ~T return type for async functions
• ~{ stmts } async blocks
• .await postfix operator
• TaskSystem.run() sync bridge

Background Execution (Plan 126)

• .go postfix operator spawns to worker pool
• Capture semantics: Copy types auto-copied, non-Copy require explicit .move or .clone()

Notes

• TaskDef struct has attrs (Vec<TaskAttr>), state (Vec<(Name, bool, Expr)>), start_hook, stop_hook, on_block
• TaskOnBlock has context_param (for Phase 3 style), handlers (Vec<(TaskMsgPattern, guard, Body)>), else_handler
• Ask/Reply uses compile-time oneshot channel rewriting