The Prolog interface is based on the idea of a Prolog server that provides its service by answering queries from external applications (typically Java applications). The Prolog interface in PrologBeans is defined in library(prologbeans), which implements the Prolog server and exports the following predicates:
starts the Prolog server using the options specified. Please
start/[0,1] will not return until a server shutdown
occurs. Options should be a list of zero or more of:
an integer denoting the port number of the Prolog server. The default
port, if no port option is present, is 8066. In the case of the
default port being used, the Socket Reuse Address bit will be set in
the underlying sockets layer. If
Val is a variable,
then some unused port will be selected by the OS, the actual port number
can be obtained with
get_server_property/1, typically from a
server_started event listener.
a list of atoms denoting the hosts (in form of IP-addresses) that are
accepted by the Prolog server (default:
an integer denoting the duration of a session in seconds. The session will be
removed if it has been inactive more than this timeout when the
session garbage collect starts. If the session timeout is set
to zero, then there will be no garbage collection of sessions
an integer denoting the minimum time in seconds between two consecutive
session garbage collections. If the timeout is set to zero, then there will
be no garbage collection of sessions (default:
:- start([port(7500), accepted_hosts(['127.0.0.1','22.214.171.124'])]).
shuts down the server and closes the sockets and the streams after processing all available input. There are three modes:
as soon as possible (default).
after all sessions have ended (all sessions have either been explicitly removed by request of the client application, or they have been garbage collected). Please note: there can still be connections to the Prolog server even when all sessions have ended.
after all connections to the Prolog server are closed. Please note: there can still be user sessions left when all connections have been closed.
register_query(+Query, :PredicateToCall, +SessionVar)
registers a query and the corresponding goal. Before the
registration, any previously registered query matching Query
will be removed (as if by
goal PredicateToCall will be called when a query matching
Query is received.
Typically, Query and PredicateToCall share variables that
are instantiated by the call, and the instantiated Query
is passed back to the client. In general, variable bindings can be
arbitrary Prolog terms, including terms containing unbound variables.
However, any unbound variables with attributes or blocked goals
attached to them will be replaced by plain, brand new variables. This
is analogous to the way attributed variables are handled in terms that are
written, copied, asserted, gathered as solutions to
and friends, or raised as exceptions. If the attributes must be passed
to the client, then the Prolog code can obtain them by using
copy_term/3 (see ref-lte-cpt).
The goal is called determinately, i.e. it is never backtracked into.
If it fails, then the term
no is passed to the client instead of the
instantiated Query. If it raises an exception E, then
error(E) is passed to the client instead of the
Before calling the query, the variable SessionVar, if given, is bound to the id of the current session. Session ids are typically generated in web applications that track users and mark all consecutive web-accesses with the same session id.
unregisters all queries matching Query.
session_get(+SessionID, +ParameterName, +DefaultValue, -Value)
returns the value of a given parameter in a given session. If no value exists, then it will return the default value. Arguments:
is the id of the session for which values have been stored
an atom, is the name of the parameter to retrieve
is the value that will be used if no value is stored
is the stored value or the default value if nothing was stored
session_put(+SessionID, +ParameterName, +Value)
stores the value of the given parameter. Please note: any pre-existing
value for this parameter will be overwritten. Note that
session_put/3 will not be undone when backtracking (the current
implementation is based on
is the id of the session for the values to store
an atom, is the name of the parameter to store
the value to be stored
register_event_listener(+Event, :PredicateToCall, -Id)
PredicateToCall to be called (as if by
once(PredicateToCall)) when the event matching
(event matching is on principal functor only). If the goal fails or
raises an exception, then a warning is written to
user_error but the failure
or exception is otherwise ignored. Arguments:
is the event template; see below.
an arbitrary goal.
becomes bound to a (ground) term that can be used with
unregister_event_listener/1 to remove this event listener.
The predefined events are as follows:
called before the first call to a query for this session
called before the session is about to be garbage collected (removed)
called when the server is about to start (enter its main loop)
called when the server is about to shut down
Attempt to register an event listener for other events than the predefined events will throw an exception.
More than one listeners can be defined for the same event. They will be called in some unspecified order when the event occurs.
Unregister a previously registered event listener. The Id is the
value returned by the corresponding call to
register_event_listener/3. It is an error to attempt to
unregister an event listener more than once.