Rootfinding based events

In NeuroML, we do

            <StateVariable name="spiking" dimension="none"/>
            <OnCondition test="v .gt. thresh .and. spiking .lt. 0.5">
                <StateAssignment variable="spiking" value="1"/>
                <EventOut port="spike"/>
            </OnCondition>

            <OnCondition test="v .lt. thresh">
                <StateAssignment variable="spiking" value="0"/>
            </OnCondition>

to detect spikes. This involves the creation of a new state variable, and some "ad hoc" logic. This degree of "imperativeness" seems to go against the declarative philosophy of NeuroML/LEMS.
I would suggest defining and detecting events as zero-crossings of state functions in a given direction, i.e., we would just need to say something like

            <OnCondition test="v - thresh" direction="increasing">
                <EventOut port="spike"/>
            </OnCondition>

this would simplify the component, but jLEMS would then need to store history in order to detect events. @robertcannon, would that require drastic changes to the interpreter?

Start by reading the jLEMS interpreter's handling of NeuroML OnCondition events and determine how event conditions are currently evaluated. Trace what changes would be required to detect zero-crossings and retain the needed history. Done means the scope and impact of supporting directional rootfinding events are documented clearly enough for implementation.