An event with a memory — the [latch] table

An optional top-level [latch] table declares named armed-and-fired events (ADR-0137). It sits beside [smoothing] in every sense: same place in the file, same resolved-once-at-load treatment, same reset on a preset switch — and it answers the question [smoothing] cannot, because easing shapes a value over time without ever holding one.

[latch]
recut = { arm = "mod(time, 100) > 90", fire = "onset > 0.6", hold = 0.5 }

[params]
recompose = "recut"

key	value	meaning
arm	expression	Above 0.5 opens an arming window; the fall closes it, the next rise opens a new one. Required.
fire	expression	The latch fires on this expression’s rising edge inside an open window. A value already above 0.5 when the window opened is not an edge. Required.
hold	seconds	How long the fired latch reads 1.0. A bare number, not an expression. Optional; default 0, which is a single frame.

The name on the left is yours, and it becomes an ordinary variable in every expression of the preset — [params], [per_vertex] and [layer.params] — so it multiplies, gates, eases through [smoothing], and can be read by several bindings at once.

The property, stated once because everything else follows from it: one rise per arming window. However many fire edges a window contains, the latch rises on the first and on no other, and the next rise requires arm to have fallen and risen again. A window with no fire edge in it produces no rise at all. That is what separates a latch from min(arm_expr, fire_expr), which goes true on every onset in the window.

hold runs on real elapsed time, so it is the same duration at any refresh rate, and it is validated non-negative and finite at load.

The cap is four latches per preset. That is a chosen number rather than a measured one — as many independent events as a preset can hold in one reader’s head — and the storage behind it is a fixed block resolved at load, so asking for a fifth is a load error naming the cap rather than a slower path. Two further load errors, both there to stop a binding silently reading something else: a latch name that the grammar already resolves (bass, time, pi, sin, …) is rejected, and a latch’s arm/fire may not name another latch.

A latch is the one part of the preset surface whose value depends on the frames before this one. The state lives in the render layer beside the smoothers, never inside the expression, so the evaluator is unchanged — but two things follow that no other table has.

A single-frame probe reads a latch at rest. Anything evaluating one frame in isolation sees 0.0 and cannot distinguish a latch that can never fire from one that has not fired yet. shot --report drives a frame sequence and does see a latch; a one-frame reading does not.

A latch nothing reads is a load warning, in the shape an inert [occupancy] exempt entry gets and for the same reason: you would otherwise believe an event was wired up while nothing consumed it.