1.5. Effects🔗

The effect system (MailboxActors.Effect) describes side-effects produced by a single behaviour step. Effects form an inductive type with seven constructors:

• noop — no observable action,

• send j target payload — enqueue a message for engine type j,

• update env — replace the engine's local environment,

• spawn j cfg state — create a new child engine of type j,

• mfilter f — transition to ready f, installing a new acceptance filter,

• terminate — signal engine termination,

• chain e₁ e₂ — sequence two effects.

The chain constructor gives effect composition without requiring a monadic bind; the semantics evaluates e₁ first, then e₂ on the resulting state.