Module Ports

openPort :: Port a -> [a] -> Bool   

Opens an internal port for communication.

Example call:

(openPort p s)

Parameters:

• p : a free variable which will be constrained with the port messages
• s : a free variable which will be instantiated to the stream of incoming messages

send :: a -> Port a -> Bool   

Sends a message to a port.

doSend :: a -> Port a -> IO ()   

I/O action that sends a message to a port.

Further infos:

• might behave indeterministically

ping :: Int -> Port a -> IO (Maybe Int)   

Checks whether port p is still reachable.

Example call:

(ping n p)

Parameters:

• n : the time to wait for reachability in milliseconds
• p : a port to be checked for reachability

Returns:

Nothing if port p is unreachable within n milliseconds, or (Just m) if port p could be contacted within m milliseconds

timeoutOnStream :: Int -> [a] -> Maybe [a]   

Checks for instantiation of a stream within some amount of time.

Example call:

(timeoutOnStream n str)

Parameters:

• n : the time to wait for instantiation in milliseconds
• str : the stream to be checked for instantiation (usually the stream of incoming messages at some port)

Returns:

(Just str) if str is instantiated within n milliseconds, or Nothing otherwise

openProcessPort :: String -> IO (Port SP_Msg)   

Opens a new connection to a process that executes a shell command.

Example call:

(openProcessPort cmd)

Parameters:

• cmd : the shell command to be executed

Returns:

the output/input stream (represented as a stream port) that is connected to the standard input/output of the process performing the execution of cmd.

openNamedPort :: String -> IO [a]   

Opens an external port with a symbolic name.

Example call:

(openNamedPort portname)

Parameters:

• portname : the symbolic name under which the port is accessible (any string without occurrences of @)

Returns:

the stream of incoming messages at this port

connectPortRepeat :: Int -> IO a -> Int -> String -> IO (Maybe (Port b))   

Waits for connection to an external port. In contrast to connectPort, this action waits until the external port has been registered with its symbolic name.

Example call:

(connectPortRepeat waittime action retries portname)

Parameters:

• waittime : the time to wait before retrying (in milliseconds)
• action : I/O action to be executed before each wait cycle
• retries : number of retries before giving up (-1 = retry forever)
• portname : the symbolic name of the external port (must be either of the form "name@machine" or "name" where the latter is a shorthand for "name@localhost")

Returns:

Nothing (if connection is not possible within the given limits) or (Just p) where p is a port with the symbolic name portname

connectPortWait :: String -> IO (Port a)   

Waits for connection to an external port and return the connected port. This action waits (possibly forever) until the external port is registered.

Example call:

(connectPortWait portname)

Parameters:

• portname : the symbolic name of the external port (must be either of the form "name@host" or "name" where the latter is a shorthand for "name@localhost")

Returns:

a port with the symbolic name portname

connectPort :: String -> IO (Port a)   

Connects to an external port. The external port must be already registered, otherwise an error is reported.

Example call:

(connectPort portname)

Parameters:

• portname : the symbolic name of the external port (must be either of the form "name@host" or "name" where the latter is a shorthand for "name@localhost")

Returns:

a port with the symbolic name portname

choiceSPEP :: Port SP_Msg -> [a] -> Either String [a]   

This function implements a committed choice over the receiving of messages via a stream port and an external port.

Note that the implementation of choiceSPEP works only with Sicstus-Prolog 3.8.5 or higher (due to a bug in previous versions of Sicstus-Prolog).

Example call:

(choiceSPEP sp ms)

Parameters:

• sp : a stream port sp
• ms : a stream of messages received via an external port

Returns:

(Left s) if s is an input line received at the stream port (via SP_GetLine) or

(Right ms) if the stream ms is instantiated

with at least one new message at the head

newObject :: (a -> [b] -> Bool) -> a -> Port b -> Bool   

Creates a new object (of type State -> [msg] -> Bool) with an initial state and a port to which messages for this object can be sent.

Example call:

(newObject object state port)

Parameters:

• object : an object template
• state : the initial state of the object
• port : a free variable which will be constrained to the port for sending messages to the object

newNamedObject :: (a -> [b] -> Bool) -> a -> String -> IO ()   

Creates a new object (of type State -> [msg] -> Bool) with a symbolic port name to which messages for this object can be sent.

Example call:

(newNamedObject object state portname)

Parameters:

• object : an object template
• state : the initial state of the object
• portname : the symbolic name under which the object's port is accessible (any string without occurrences of @)

runNamedServer :: ([a] -> IO b) -> String -> IO b   

Runs a new server (of type [msg] -> IO a) on a named port to which messages can be sent.

Example call:

(runNamedServer server portname)

Parameters:

• server : a server function that processes incoming messages
• portname : the symbolic name under which the server's port is accessible (any string without occurrences of @)