Every expression that is evaluated at evaltime returns a result, which may or may not change at runtime. There are three kinds of results in alv.

Constants

Constant results contain a single value that is generated at evaltime and do not change at runtime. Operators that involve only constants generally result in constants as well and are not processed at runtime. Literal strings and numbers are constants.

Constants are denoted using the equals symbol (=) in documentation and traces, e.g:

(trace 4)

trace 4: <num= 4>

where <num= 4> denotes a constant of the type num with a value of 4.

The = builtin can be used to assert that a result is a constant. There is no way to convert a signal or event stream to a constant.

Signal Streams (~-streams)

Signal results contain a continuous value of a given type. A signal must have a defined value at any given moment in time, including each evaltime evaluation. While signals are considered to be continuous, for optimizations sake they are processed as a series of discrete changes. Operators with signal inputs generally are only reevaluated at runtime when the signal changed.

Signals are denoted using the tilde symbol (~) in documentation and traces, e.g.:

(import* time)
(trace (lfo 2))

trace (lfo 2): <num~ 0.0>
trace (lfo 2): <num~ 0.0016211131633209>

where <num~ 1.0> denotes a signal-stream of the type num with a current value of 1.0.

The ~ builtin can be used to convert event streams to signal streams that track the last received event. It is not possible or necessary to convert constants to signal streams, as constants can always be passed in place of signals.

Event Streams (!-streams)

Event results may contain discrete values at instants in time, but are undefined between such occurences. All values in a single event result share one type. During a single tick of the alv scheduler, a given event result may contain zero or more ordered values. Operators with event inputs must operate each incoming event separately, as each event is considered to occur in a separate moment.

Event streams are denoted using the bang symbol (!) in documentation and traces, e.g.:

(import* time)
(trace (every 2))

trace (lfo 2): <bang! true>
trace (lfo 2): <bang! true>

where <bang! true> denotes an event-stream of the type bang that fired with a value of true.

The ! builtin can be used to convert signal streams or constants into events by using an external impulse source.