New constructions

Logic

Temporal terms

Guards and scripts

Hints

Syntax

Temporal terms

• fileContents(CONTENT, FILENAME) - unifies first argument with FILENAME contents. ET-Prolog would install watch and if it would get urgent read signal, file would be read again from the beginning. This is useful for reading files from /sys. Standard ET-Prolog library for n900 has following terms based on fileContents:
  • headphonesState(STATE) - unifies first argument with headphones (and av cable) socket.
  • slideState(STATE) - unifies first argument with keyboard status (open/closed)
  • shutterState(STATE) - unifies first argument with status of camera shutter
• pollFile(STATE, FILENAME) - unifies first argument with FILENAME contents. File is reread on every first invocation per epoch. Standard ET-Prolog library for n900 has following terms based on pollFile:
  • proximitySensor(STATE) - unifies proximity sensor state with first argument.
• intFile(LIGHT, FILENAME, TIME, MEASURES) - pollFile modification, which reads integer number from file. Number is read MEASURES times during TIME (in 1/1000 seconds), and LIGHT is unified with average value. Standard ET-Prolog library for n900 has following terms based on intFile:
  • lightSensor(LIGHT, TIME, MEASURES) - unifies first argument with value from ambient light sensor.
• temporalTerm(VALUE, NAME) - temporal term, which can be controlled from prolog or through DBus.

Using temporalTerm

newTemporalTerm(NAME, INITIAL_VALUE)

addHint(NAME, VALUE)

addDBusHandler(SERVICE, OBJECT_PATH, INTERFACE, METHOD, IS_EVENT, TEMPORAL_TERM)

addDBusListener(TYPE, OBJECT_PATH, INTERFACE, METHOD, IS_EVENT, USE_SYSTEM_BUS, TEMPORAL_TERM)

• TYPE - type of event to listen to. Can be signal or method_call
• OBJECT_PATH, INTERFACE, METHOD - describe what DBus signals you want to receive. Use empty string '' as a wildcard
• IS_EVENT have the same meaning as for addDBusHandler
• USE_SYSTEM_BUS - if true system bus would be used, otherwise session bus would be used

Adding guards

• alwaysGuard - always returns true
• changedGuard - returns true if value has been changed
• decreasedGuard - returns true if value decreased
• equalGuard(VALUE) - returns true if term value is equal to VALUE
• greaterGuard(VALUE) - returns true if term value is more than VALUE
• increasedGuard - returns true if value increased
• intervalGuard(A, B) - returns true if value is between A and B
• lessGuard(value) - returns true if term value is less than VALUE
• nEqualGuard(value) - returns true if term value is not equal to VALUE
• sameGuard - returns true if term value didn't change
• guards are bind to terms with

  addGuard(TEMPORAL_TERM, [[GUARD, ARGS...], [GUARD, ARGS...]...], SCRIPT, TRIGGER_ON_CHANGE)

  • TEMPORAL_TERM - temporal term to which you bind guards
  • [[GUARD, ARGS...], [GUARD, ARGS...]...] - guards list. ARGS - argument list, passed to temporal term. Currently used only for GpsTerm
  • SCRIPT - path to script, that should be executed
  • TRIGGER_ON_CHANGE if true, then script is executed on every guards conjunction change, if false, script is executed if guards conjunction is true
  For example

  addGuard(temporalTerm(_, 'manual_timer'), alwaysGuard, 'logic/manual.pl', false)

  Alternatively you can use

  addChangeGuard(TEMPORAL_TERM, [[GUARD, ARGS...], [GUARD, ARGS...]...], SCRIPT, TRIGGER_ON_CHANGE)

  which works like addGuard, but script is triggered on guards conjunction change.

  Working with timers

  If you need to check term value on regular basis you can send it hints with predefined intervals. Use following predicates

  addTimerHint(TERM, INTERVAL)

  for adding timer for TERM and

  delTimerHint(TERM, INTERVAL)

  for removal.

  Sending DBus signals

  As far as main interprocess communication tool in maemo is DBus, ET-Prolog allows to send DBus signals. It can e done by means of

  dbusSend(SERVICE, OBJECT_PATH, INTERFACE, METHOD, SIGNAL)

  where first 4 arguments describe signal destination (for additional information see DBus documentation), and SIGNAL - is data that should be attached to signal. SIGNAL must be a list, ET-Prolog performs automatic conversion from prolog types to DBus types. The only problem is that SWI-Prolog doesn't have syntax for defining strings, so if you want to send a sting you have to do like this:

  string_to_atom(PROFILE, 'silent'),
  dbusSend('com.nokia.profiled', '/com/nokia/profiled', 'com.nokia.profiled', 'set_profile', [PROFILE])

  Temporal operators

  Temporal operator are used for access to temporal term values history. Following operators are defined:
  • previous - calculates value, that was an epoch ago. You can apply this operator arbitrary number of times in recursion.
  • always - returns true if argument is true in all epochs (not including old epochs deleted that free resources).
  • sometimes - returns true if argument was true at least in one previous epoch.
  Due to limitations of C++ SWI-Prolog interface and simple lack of time, multivalue predicates are not supported inside temporal terms (at least now). If you want to calculate several predicates you have to enclose them in additional parenthesis so as not to break syntax:

  previous((
  	temporalTerm(OLDVALUE, 'manual'), 
  	write('Previous manual term value:'),
  	write(OLDVALUE),
  	nl))

  Cleaning memory

  If you don't need temporal term any more you can delete it with

  deleteTerm(TEMPORAL_TERM)

  Beside this, old values are cleared automatically. By default values older than half an hour are deleted, if there are never values. This setting can be adjusted with -t command line argument.

  Working with maemo libraries

  alarmd - events based on alarms

  Работа с таким событием состоит из двух этапов: создания события и его использования. Создается оно предикатом

  newAlarmTerm(NAME, IS_EVENT, SCHEDULE)

  Где NAME задает имя события, IS_EVENT определяет является ли это событие точкой во времени (значение истина), либо периодом (значение ложь). SCHEDULE описывает расписание, по которому событие наступает. Для случая IS_EVENT=true расписание имеет вид

  (DD.MM.YYYY HH:MM;...)

  причем вместо каждого значения можно указать *, что будет означать "любое значение", либо перечислить допустимые значения через запятую. Причем в качестве дня можно указывать как даты, так и дни недели. Т.е. "(5,wed.4,8,12.* 15:00)" означает "по средам и 5го числа 4го, 8го и 12го месяцев любого года в 15 часов". Вы можете указать несколько таких условий через точку с запятой, однако все они должны иметь одинаковый год.
  Для случая IS_EVENT=false расписание имеет вид

  (DD.MM.YYYY HH:MM;...)-(DD.MM.YYYY HH:MM;...)

  Где в первых скобках указаны моменты времени, когда интервал начинается, а во вторых, когда он заканчивается.
  Для получения значения терма используйте

  alarmTerm(VALUE, NAME)

  liblocation - GPS

  Following two predicates for working with GPS are defined:

  gpsConfig(METHOD, INTERVAL)

  where METHOD - method used for determining location. Can be CWP, ACWP, GNSS, AGNSS. And INTERVAL sates, how often location would be reported. See documentation for additional information
  Second term allows you to get information about current location:

  gpsFix(VALUE, FIELD)

  Where FIELD is a name of LocationGPSDeviceFix field which you want to get. Allowed values are: mode, time, time_set, ept, latitude, longitude, latlong_set, altitude, altitude_set, epv, track, track_set, epd, speed, speed_set, eps, climb, climb_set, epc. VALUE would be unified with the field.
  When you add guards to GpsTerm you need to specify which field every guard should use. For example following code adds guard which is true, when you are near Moscow State University:

  addGuard(gpsFix(_, 'mode'), [[equalGuard(true),'latlong_set'],[greaterGuard(55.71129),'latitude'],[greaterGuard(37.49922),'longitude'],[lessGuard(55.69145),'latitude'],[lessGuard(37.56634),'longitude']], 'logic/nearUniversity.pl', false)

  Conclusion

  This documentation can be incomplete. We could forget to describe some predicates or forget to write about some useful tips. But this is first beta release of ET-Prolog. If something is not clear, you can try look in the sources.