# Actions Specifications¶

Actions are commands and computations performed by Antescofo at a certain point in time. Often, theses actions are messages sent to a MAX/PD object to trigger other activities. Other actions correspond to internal computations. Actions can be also used to specify the temporal organization of subsequent actions.

Actions can be categorized as instantaneous or durative:

• an instantaneous action takes no time to be performed (see the Synchrony hypothesis);

• a durative action is an action that takes times to be performed.

However, another relevant categorization is atomic or compound:

• An atomic action performs an elementary computation or a simple message passing that cannot be decomposed.

• A compound action groups other ‘‘child actions’’ allowing for polyphony (i.e. actions that are interleaved in time or that are are performed in parallel), loops (i.e. actions that are iterated and repeated in time), conditional actions, etc.

An atomic action is always instantaneous. Usually, a compound action takes time to be performed. Howevever, some compound actions may be instantaneous (for example, a conditional action that involves only one atomic action without delay.

## Action Sequence¶

Actions always appear in sequences called groups. A group organizes the performance of its actions in time. Some groups are explicit when they are introduced with the Group construction (the fundamental compound action). Or they can be implicit:

• as the sequence of actions that appears after a musical event,

• as the children of other compound actions: Loop, Whenever, etc.,

• as the body of a process,

• as the @action clause of a Curve,

• as an @abort clause of a compound action,

• as an @init clause, a @whenever clause or as the body of a method in an object.

An action within a sequence of actions:

• Starts with an optional delay

• is linked with the previous action through a continuation operator. They are currently three continuation operators:

•   (nothing, the two actions appears in sequence in the text) which specifies that the action that follows starts with the begining of the previous one;

• ==> which triggers the next action with the end of the previous one;

• and +=> which launches the next action at the end of the previous one including its children.

In addition, actions have optional attributes that are specified differently depending on whether the action is atomic or compound.

A sequence of actions may also defines variables and temporal variables anywhere in the sequence. These definitions are not actions and takes no time in the computations.

## A Glimpse of Syntax¶

### Actions Sequence¶

Sequence of actions appear after a musical event or as the body of a compound action. They are made explicit with the notion of Group which is used to specify additional properties of the sequence (e.g. synchronization attributes).

The @local, @global and @tempovar keywords introduce variables declaration. The local variables are local to the sequence of actions where the declaration appears, and global variables can be accesssed from anywhere. The keywords @local and @global are also attributes of an action, see below.

### Atomic Action¶

These actions are further described in chapter Atomic Actions. They are performed instantaneously.

### Compound Action¶

These actions are further described in chapter Compound Actions. They act as temporal containers organizing the temporal relationships of other actions that are called child's of the container.

## Action Attributes¶

Each action has some optional attributes which appear as a comma separated list:

        Group G  @att₁, @att₂ := value  { }
atomic_action  @att₁, @att₂ := value
compound_action @att₁, @att₂ := value { ... }


In this example, @att1 is an attribute limited to one keyword, and @att2 is an attribute that requires a parameter. The parameter is given after the optional := sign.

Some attributes can be used on any actions:

• @local and @global attributes specify the behavior in the handling of missed events and in fastforward mode, see antescofo_is_in_rehearsal_mode.

• the @latency attribute alters the computation of delays to compensate latency.

• synchronization attributes may alter all actions, incuding atomic ones. Most of them are useless on an atomic action, like the specification of a tempo. As a rule of thumb, the effect of synchronization attributes on an atomic action is achieved by putting this action as the sole action of a group with this attribute.

Other attributes are specific to some kind of actions. There are listed below and they are described in the section dedicated to this kind of action:

The following diagrams gives the syntax of these attributes:

Attributes Meaningfull on All Actions

Curve Specific Attributes
@grain is a mandatory attributes but not @action.

Whenever Specific Attributes

Process Definition Specific Attributes

Abort Specific Attributes

Compound Actions Specific Attributes

Synchronization Specific Attributes

### Labels¶

There is one additional attribute that can be specified for all actions: a label. The label of a compound action usally follows the keyword introducing the compound action. This is confusing for some compound action like the if. However, the label can also be specified with the @label attribute:

       action ... @label := a_label
action ... @label := "a label"


(this is the only way to give a label to an atomic action or to an if or a switch).

Labels are used to refer to an action, for instance to terminate it. Like events, actions can be labeled with:

• a simple identifier,

• a string,

• an integer.

There can be several labels for the same action. Unlike with event labels, the $-identifier associated to the label of an action cannot be used to refer to the relative position of this action in the score. ## Delays¶ An optional specification of a delay can be given before any action A. This defines either • ordinary delays represent the time to wait between the previous event or action in the score and the start of the calculation of A; • date_delays start with a § and represents the time to wait between the origin of A and its computation. Date delays are internally rewritten in ordinary delays and are merely a convenience of writing. In either case, delays can be expressed in beats (relatively of a tempo), seconds or milliseconds. ### Ordinary delays¶ The countdown of the delay will start from either the beginning or the end of the previous action following the continuation operator that links the two actions. See section Continuation Operator for more information. If the action is triggered by an event, the timer countdown should start as soon as the event is recognized. For the rest of this section, we assume a default continuation: delays are counted from the start of the previous action. Upon the expiration of the delay, we say that the action is fired (we use also the word triggered or launched). Thus, the following sequence  NOTE C2 2.0 d₁ action₁ d₂ action₂ NOTE D2 1.0  specifies that, in an ideal performance that adheres strictly to the temporal constraint specified in the score, action₁ will be fired d₁ after the recognition of the C2 note, and action₂ will be triggered d₂ after the firing of action₁. That is to say, action₂ is fired d₁ + d₂ after the recognition of C2. A delay can be any expression. This expression is evaluated when the preceding event is launched. That is, expression d₂ is evaluated in the logical instant where action₁ is computed. If the result is not a number, an error is signaled. ### Zero Delay¶ The absence of a delay is equivalent to a zero delay. A zero-delayed action is launched synchronously with the preceding action or with the recognition of its associated event. Synchronous actions are performed in the same logical instant and last zero time, cf. paragraph Logical Instant. ### Negative Delay¶ The delay to wait to launch an action can be negative for three reason: • the value of the delay is really negative, • there is a latency compensation mechanism at work, see @latency, • or the action is launched lately because it is triggered by a missed event, see Missed Event Errors Strategie. In this case, the action is launched immediately in late mode: global actions are launched but not local actions and the time lag is propagated to the next one, until delays becomes positive again, in which case the continuation of the actions is processed in normal mode. For instance, in  a₀ -1 a₁ 4 a₂  a₁ will be launched late, that is, right after the launch of a₀ but a_2 will be launched in normal mode after a delay of $3$ (computed as $4 + (-1)$) starting from a₀. ### Absolute and Relative Delay¶ A delay can be either absolute or relative. An absolute delay is expressed in seconds (or in milliseconds) and refers to wall clock time or physical time. The qualifier (s or ms, respectively) is used to denote an absolute delay:  a₀ 1 s a₁ (2*$v) ms a₂


Action a₁ occurs one second after a₀ and a₂ occurs (2 * $v) milliseconds after a₁. If the qualifier (s or ms) is missing, the delay is expressed in beat and it is relative to the tempo of the enclosing group. ### Evaluation of a Delay¶ In the previous example, the delay for a₂ implies a computation whose result may depend of the date of the computation (for instance, the variable $v may be updated somewhere else in parallel). So, it is important to know when the computation of a delay occurs: it takes place when the previous action is launched, since the launching of this action is also the start of the delay. And the delay of the first action in a group is computed when the group is launched.

A second remark is that, once computed, the delay itself is not reevaluated until its expiration. However, the delay can be expressed in the relative tempo or relatively to a computed tempo and its mapping into the physical time is reevaluated as needed - that is, when the tempo changes.

Delay vs. Expressions. The expression used in the specification of a delay, and more generally of a duration1, must evaluate to a numeric (integer or float). There no specific type of values corresponding to a delay.

This means that 1 s is not a value. The s or ms qualifier appears in the specification of a delay, but is not part of the expression defining the duration of the delay. A consequence is that you cannot pass 1 s as the value of an argument (however, you can pass 1).

### Synchronization Strategies¶

Delays can be seen as temporal relationships between actions. There are several ways, called synchronization strategies, to implement these temporal relationships at runtime.

For instance, assuming that in the first example of this section action₂ actually occurs after the occurrence of NOTE D, one may count a delay of $d₁ + d₂ - 2.0$ starting from NOTE D after launching action₂. This approach will be for instance more tightly coupled with the stream of musical events. Synchronization strategies are discussed in chapter Synchronization Strategies.

### Date delays¶

Date delays differ from ordinary delays by starting the waiting time not from the previous action, but from the origin of the sequence of actions.

The origin of an action is the event or action that is reached by going up the sequence of previous actions, staying in the same group of actions, until reaching an action without a predecessor.

Date delays are rewritten in ordinary delays and the previous consideration on ordinary delays also apply on date delays. They are merely a convenience. Imagine for instance a sequence of actions: the first one launches a sample, and the others one open or close some effects at predetermined date in the sample. It would be painful to express the datation of these actions relatively from one to the other. It is much simpler to express their datation from the launch of the sample, that is, from the first action. It can be done with date delays:

   action₁
§ d₂ action₂
§ d₃ action₃
§ d₄ action₄


_which is equivalent to
and implemented as_
action₁
d₂ action₂
(d₃ -  d₂) action₃
(d₄ - (d₃ -  d₂)) action₄


The § character is an abbreviation which avoids to make explicit the computation of the date. This computation is done internally by Antescofo and its transparent for the user. However, this translation must be kept in mind: for instance, synchronization strategies apply to the ordinary delays computed from the date delays.

Ordinary delays and date delays can be mixed:

   action₁
§ d₂ action₂
d₃ action₃
§ d₄ action₄


_which is equivalent to
and implemented as_
action₁
d₂ action₂
d₃ action₃
(d₄ - (d₂ + d₃)) action₄


However, it is not possible to mix absolute and relative delay if there are date delays: the delays of the actions in the involved sequence must be all absolute or all relative:

   d₁ s  action₁  ; ERROR: there is an absolute ordinary delay
§ d₂ action₂   ; and a relative date delay in the same sequence
d₃ action₃     ; of actions
§ d₄ s action₄


Date delays are computed and can be negative: they are then handled as explained above. Some of these computations can be done statically (if all the delays involved are constant expressions). In this case, the detection of a negative delay will raise a warning:

       action₁
3 action₂
§ 1 action₃ ; the equivalent ordinary delay is (1 - 3) = -2


However, all such negative delays cannot be statically detected.

## When an Action is Performed¶

We write at the beginning of this chapter that actions are performed when arriving at some date. The specification of this date is always a delay starting from some internal or external event:

• the occurrence of a musical event (detected by the listening machine)

• the change of a musical parameter (i.e., the tempo)

• the start or the end of another action

• the reception of an OSC message

• a logical event (see the whenever construction and the chapter Patterns) triggered by an internal update (via :=) or an external update (via the setvar message)

• the reception of a message from the host environment (Max, PD)

• the signal spanned by an abort action (see @abort handlers)

• the sampling of a Curve

• the instance of an iterative construct Loop and Forall

• the launch of a process (cf. Processes) or the creation of an object (cf. Objects)

In addition, for delays and for durative actions, the passing of time depends on a temporal scope which defines a tempo, a synchronization strategy and other temporal parameters. These notions are investigated in chapter Synchronization.

1. used for the period of a Loop and in the breakpoint of a Curve