KSLCore/ksl.modeling.decision/Neutral

Neutral

sealed interface Neutral<in T>(source)

Every lever declares what doing nothing means. This is the repair §8.2.3 specifies, and it is a required argument rather than an optional one.

Before it, a lever had an optional read and the design inferred everything from whether a modeler had supplied one. That conflated two different facts — no reader was given and there is nothing to read — with three measured consequences (§8.2.2): HoldCurrentPolicy could not run at all on a transactional model, so the Level-2 safety argument of §6.2 was unavailable for the canonical MDP example; §4.1.2.3's advice to always supply a reader pushed a modeler toward supplying a meaningless one; and having done so, the no-op elision silently dropped 1.5% of orders.

Naming the neutral value resolves all of it, because the reader stops being a separate optional thing and becomes the content of one of the two cases.

Inheritors

Current

Value

Types

Current

class Current<T>(val read: T.() -> Double) : Neutral<T>

A LeverKind.SETTING. Doing nothing is "leave it where it stands", so a reader is required — structurally, since there is nowhere else to put it, rather than by advice that a modeler may decline.

Value

class Value<T>(val amount: Double) : Neutral<T>

A LeverKind.TRANSACTION. Doing nothing is a declared constant, almost always zero. Nothing is read, and supportsCurrentValue = false now records a fact about the lever instead of an omission by its author.