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--- alvis:in [2013/12/15 00:09]
marcin
+++ — (current)
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-====== In statement ======
-An agent can communicate with its outside world using **ports**. Each port can be used both as an input or an output one. The current role of a port is determined by two factors:
-  - Connections to the port in the corresponding communication diagram -- e.g. if a port ''p'' is used only as an input port for an one-way connection, it cannot be used as an output port.
-  - Statements used in the code layer -- e.g. if a port ''p'' is used only as an argument of the **in** statement, it is an input port even if all its connections are two-way ones.
-Any communication through a port can be a **pure communication** or a **value passing combination**.
-In case of a **pure communication**, the **in** statement collects a signal (without specified value) through the statement port.
-In case of a **value passing communication**, the **in** statement collects a value through the statement port (probably of a composed type) and assigns it to the statement parameter.
-The **in** statement is a single-step statement.
-<code>
-in p;
-in p x;
-</code>
-**Listing 1. ** In statement syntax: ''p'' stands for a port name and ''x'' stands for a parameter name
-===== Example 1 =====
-{{:alvis:example3.png|}}
-**Figure 1. ** Example 1 communication diagram
-<code>
-agent A {
-  out a;
-}
-agent B {
-  in b;
-}
-</code>
-**Listing 1. ** Example 1 code layer
-The only task of the ''A'' agent is sending a signal through its port ''a'' and the only task of the ''B'' agent is collecting a signal through its port ''b''.
-A communication between two active agents can be initialised by any of them. The agent that initialises it, performs the **out** statement to provide some information and waits for the second agent to take it, or performs the **in** statement to express its readiness to collect some information and waits until the second agent provides it.
-**[[:alvis:manual|Go back]]**