## Message passing to Max/PD

The simplest form of action in Antescofo is sending some values to a receive object in MAX or PD. This way, Antescofo acts as a coordinator between multiple tasks (machine listening and actions themselves) attempting to deliver actions deterministically as they have been authored despite changes from musicians or controllers. These actions are simply equivalent to message boxes and their usage is similar to cue list object in MAX/PD with the extension of the notion of Delay. They take the familiar form of:

          <optional-delay> <receiver-name> <message-content>

Since such actions are destined for interaction with external processes (in MAX/PD), we refer to them as external actions. External actions includes also sending an OSC message or writin data in some file, see below.

### Message Receiver

A MAX/PD message starts by an optional delay followed by a symbol refering to a MAX or PD receiver. This identifier must be a simple identifier (that is, it cannot be a [reserved #-identifier] and must not be a reserved keywords) refering to receiver object in MAX/PD.

Alternatively, it is always possible to use an arbitrary string: the content of the string denotes the Max receiver.

For example, the following action attempts to send its message to a receiver called “print” in MAX/PD whose patch might look like the figure on its left:

    NOTE C4 1.0
       print I will be printed upon recognition of C4
       0.5 print "I will be printed next, after 0.5 beats"
       print Comma, separated, message, as in MAX

### Message arguments

What follows a receiver is a comma-separated sequence of argument list. An argument list is simply a sequence of closed-expressions, simple identifiers and @-identifiers. Antescofo follows the Max convention: a message to the receivers is sent for each argument list, that is

           print 1 2 3, 4 5 6, 7 8 9

is equivalent to the 3 messages

           print 1 2 3
           print 4 5 6
           print 7 8 9

### Message terminator

The specification of a message ends with a carriage-return (the end of the line) or a closing brace. This is important because the arguments of a message is a list of items, without separators, so a terminator is needed.

Writing a message with a lot of arguments on one line can be cumbersome. So a message can span several lines, but the intermediate lines must end with a backslash `\` which voids the following end of line.

For instance,

              $a := 1   ; This is an assignment! see below in this chapter
              print "the value of the variable a is " $a
              print and here is \
                    a (2 * $a) "nd message " \
                    "specified on 3 lines (note the \\)"

will print

              the value of the variable a is 1
              and here is a 2nd message specified on 3 lines (note the \)

In the second message of the previous example, there are 7 arguments: the first four are simple identifiers converted into the corresponding symbols, the fifth argument is evaluated into an integer and the last is a string. The backslash character has a special meaning and must be “backslashed” to appear in the string, see section String.

### Expressions in messages' arguments

Expressions are evaluated to give the arguments of the message. To avoid ambiguities, an expression in a message must be a closed expression, that is: a simple identifier, a scalar constant or an expression between parentheses.

In the previous example, the first `print` has two arguments: a string and a variable which evaluates to `1`. Each value is converted into the appropriate MAX/PD values when the message is sent:

- a simple identifier is converted into a Max/PD symbol,

- a string is converted into a MAX/PD symbol

- an integer is converted into a long

- a float is converted into a float

- a boolean is converted into a long

- a tab of size n is converted into n arguments, one for each tab element

- other Antescofo values (e.g. `map` or `nim` or functions, processes, etc.) are converted into their string representation before being sent to Max/PD.

When a string is converted into a MAX/PD string, the delimiters (the quotation marks `"`) do not appear. If one wants these delimiters, you have to introduce it explicitly in the string, using an escaped quote :

          print "\"this string will appear quoted\""

prints the following to MAX/PD console

          "this string will appear quoted"

### Computing the receiver

Sometiimes it is necessary, or just handy, to specify the receiver of a message as the result of a computation. In this case, the special construct `@command` is used:

           @command(expression) argument_sequence

This action is performed in three steps:

- first the expression in the `@command` is evaluated.

- Then the resulting value is interpreted as a string.

- At last this string is used as the Max/PD receiver of the message.

Examples of such computations often involve string concatenation, as in

           ForAll $num in (4)
           {
                @command("spat" + $num) ($param[$num))
           }

In this code, the ForAll construct iterates its body, which will send the four messages:

           spat0 ($param[0])
           spat1 ($param[1])
           spat2 ($param[2])
           spat3 ($param[3])

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