The predicates in this section provide basic access to the operating
system that has been part of the Prolog legacy tradition. Note that more
advanced access to low-level OS features is provided by several
libraries from the clib package, notably library library(process),
library(socket), library(unix) and library(filesex).
shell(Command, 0)’. See shell/2
for details.
On Windows, shell/[1,2]
executes the command using the CreateProcess() API and waits for
the command to terminate. If the command ends with a
& sign, the command is handed to the WinExec()
API, which does not wait for the new task to terminate. See also win_exec/2
and
win_shell/2.
Please note that the CreateProcess() API does not imply
the Windows command interpreter (cmd.exe and therefore commands
that are built in the command interpreter can only be activated using
the command interpreter. For example, a file can be copied using the
command below.
?- shell('cmd.exe /C copy file1.txt file2.txt').
Note that many of the operations that can be achieved using the shell
built-in commands can easily be achieved using Prolog primitives. See
make_directory/1, delete_file/1, rename_file/2,
etc. The clib package provides library(filesex),
implementing various high level file operations such as copy_file/2.
Using Prolog primitives instead of shell commands improves the
portability of your program.
The library library(process) provides process_create/3
and several related primitives that support more fine-grained
interaction with processes, including I/O redirection and management of
asynchronous processes.
all, collate, ctype, messages,
monetary, numeric or time. For
details, please consult the C library locale documentation. See also section
2.18.1. Please note that the locale is shared between all threads
and thread-safe usage of setlocale/3
is in general not possible. Do locale operations before starting threads
or thoroughly study threading aspects of locale support in your
environment before using in multithreaded environments. Locale settings
are used by format_time/3, collation_key/2
and locale_sort/2.
The messages locale defines the language used by
print_message/2.
Note that this locale is not available on all operating system. Notably
Windows does not support this category. See
win_get_user_preferred_ui_languages/2.
The predicates in this section are only available on the Windows version of SWI-Prolog. Their use is discouraged if there are portable alternatives. For example, win_exec/2 and win_shell/2 can often be replaced by the more portable shell/2 or the more powerful process_create/3.
SW_* constants written in lowercase
without the SW_*:
hide
maximize
minimize
restore
show
showdefault
showmaximized
showminimized
showminnoactive
showna
shownoactive
shownormal. In addition, iconic is a synonym
for minimize and
normal for shownormal.open,
print or explore or another operation
registered with the shell for the given document type. On modern systems
it is also possible to pass a URL as File,
opening the URL in Windows default browser. This call interfaces to the
Win32 API
ShellExecute(). The Show argument determines the
initial state of the opened window (if any). See win_exec/2
for defined values.win_shell(Operation, File, normal).DWORD,
the value is returned as an integer. If the value is a string, it is
returned as a Prolog atom. Other types are currently not supported. The
default‘root’is HKEY_CURRENT_USER. Other roots
can be specified explicitly as
HKEY_CLASSES_ROOT, HKEY_CURRENT_USER,
HKEY_LOCAL_MACHINE or HKEY_USERS. The example
below fetches the extension to use for Prolog files (see README.TXT
on the Windows version):
?- win_registry_get_value(
'HKEY_LOCAL_MACHINE/Software/SWI/Prolog',
fileExtension,
Ext).
Ext = pl
CSIDL_
and mapping the constant to lowercase. Check the Windows documentation
for the function SHGetSpecialFolderPath() for a description of
the defined constants. This example extracts the‘My Documents’folder:
?- win_folder(personal, MyDocuments). MyDocuments = 'C:/Documents and Settings/jan/My Documents'
%PATH% is extended with the provided directory.
AbsDir may be specified in the Prolog canonical syntax. See
prolog_to_os_filename/2.
Note that use_foreign_library/1
passes an absolute path to the DLL if the destination DLL can be located
from the specification using absolute_file_name/3.
This predicate is available from library library(shlib) and
can be autoloaded.
If open_shared_object/2
is passed an absolute path to a DLL on a Windows installation
that supports AddDllDirectory() and friends,150Windows 7
with up-to-date patches or Windows 8. SWI-Prolog uses LoadLibraryEx()
with the flags
LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR and
LOAD_LIBRARY_SEARCH_DEFAULT_DIRS. In this scenario,
directories from %PATH% are not searched.
Additional directories can be added using win_add_dll_directory/2.
name, the list elements are atoms. See
Language
Names for details. If Format is id, Languages
is a list of numeric language ids represented as Prolog integers. This
predicate provides Windows alternative to setlocale/3
using the category messages.
Non-portable Apple MacOS specific predicates are prefixed with
apple_.
en for
English followed by an underscore and an identifier for the Region
in the MacOS
Language & Region preferences. For example, with the
primary language set to “English (UK)” and the Region
to “United Kingdom” we get en_GB. This relates
to the locale identifier
en_GB.UTF-8. Unfortunately it is not that simple. For
example, we can combine the primary language “English (UK)” with
the
Region “Netherlands” to end up with en_NL
which is not a valid MacOS locale.
Representing time in a computer system is surprisingly complicated. There are a large number of time representations in use, and the correct choice depends on factors such as compactness, resolution and desired operations. Humans tend to think about time in hours, days, months, years or centuries. Physicists think about time in seconds. But, a month does not have a defined number of seconds. Even a day does not have a defined number of seconds as sometimes a leap-second is introduced to synchronise properly with our earth's rotation. At the same time, resolution demands a range from better than pico-seconds to millions of years. Finally, civilizations have a wide range of calendars. Although there exist libraries dealing with most of this complexity, our desire to keep Prolog clean and lean stops us from fully supporting these.
For human-oriented tasks, time can be broken into years, months, days, hours, minutes, seconds and a timezone. Physicists prefer to have time in an arithmetic type representing seconds or fraction thereof, so basic arithmetic deals with comparison and durations. An additional advantage of the physicist's approach is that it requires much less space. For these reasons, SWI-Prolog uses an arithmetic type as its prime time representation.
Many C libraries deal with time using fixed-point arithmetic, dealing with a large but finite time interval at constant resolution. In our opinion, using a floating point number is a more natural choice as we can use a natural unit and the interface does not need to be changed if a higher resolution is required in the future. Our unit of choice is the second as it is the scientific unit.151Using Julian days is a choice made by the Eclipse team. As conversion to dates is needed for a human readable notation of time and Julian days cannot deal naturally with leap seconds, we decided for the second as our unit. We have placed our origin at 1970-01-01T0:0:0Z for compatibility with the POSIX notion of time as well as with older time support provided by SWI-Prolog.
Where older versions of SWI-Prolog relied on the POSIX conversion functions, the current implementation uses libtai to realise conversion between time-stamps and calendar dates for a period of 10 million years.
We use the following time representations
-true if daylight saving time applies to the current
time, false if daylight saving time is relevant but not
effective, and -
local
to extract the local time, ’UTC’ to extract a
UTC time or an integer describing the seconds west of Greenwich.Values for month, day, hour, minute or second need not be normalized. This flexibility allows for easy computation of the time at any given number of these units from a given timestamp. Normalization can be achieved following this call with stamp_date_time/3. This example computes the date 200 days after 2006-07-14:
?- date_time_stamp(date(2006,7,214,0,0,0,0,-,-), Stamp), stamp_date_time(Stamp, D, 0), date_time_value(date, D, Date). Date = date(2007, 1, 30)
When computing a time stamp from a local time specification, the UTC offset (arg 7), TZ (arg 8) and DST (arg 9) argument may be left unbound and are unified with the proper information. The example below, executed in Amsterdam, illustrates this behaviour. On the 25th of March at 01:00, DST does not apply. At 02.00, the clock is advanced by one hour and thus both 02:00 and 03:00 represent the same time stamp.
1 ?- date_time_stamp(date(2012,3,25,1,0,0,UTCOff,TZ,DST),
Stamp).
UTCOff = -3600,
TZ = 'CET',
DST = false,
Stamp = 1332633600.0.
2 ?- date_time_stamp(date(2012,3,25,2,0,0,UTCOff,TZ,DST),
Stamp).
UTCOff = -7200,
TZ = 'CEST',
DST = true,
Stamp = 1332637200.0.
3 ?- date_time_stamp(date(2012,3,25,3,0,0,UTCOff,TZ,DST),
Stamp).
UTCOff = -7200,
TZ = 'CEST',
DST = true,
Stamp = 1332637200.0.
Note that DST and offset calculation are based on the POSIX function
mktime(). If mktime() returns an error, a
representation_error
dst is generated.
| key | value |
year | Calendar year as an integer |
month | Calendar month as an integer 1..12 |
day | Calendar day as an integer 1..31 |
hour | Clock hour as an integer 0..23 |
minute | Clock minute as an integer 0..59 |
second | Clock second as a float 0.0..60.0 |
utc_offset | Offset to UTC in seconds (positive is west) |
time_zone | Name of timezone; fails if unknown |
daylight_saving | Bool (true)
if dst is in effect |
date | Term date(Y,M,D) |
time | Term time(H,M,S) |
date(Y,M,D,H,M,S,O,TZ,DST) or a term date(Y,M,D).
aAbBcCdDeEff can be prefixed by an integer
to print the desired number of digits. E.g., %3f prints
milliseconds. This format is not covered by any standard, but available
with different format specifiers in various incarnations of the strftime()
function.FgGVhHIjklmMnOpam or pm
in lower case.PrRsStTuUwWxXyYz’%a, %d %b %Y %T %z’).
Our implementation supports
%:z, which modifies the output to HH:mm as required by
XML-Schema. Note that both notations are valid in ISO 8601. The sequence %:z
is compatible to the GNU date(1) command.Z+%
The table below gives some format strings for popular time
representations. RFC1123 is used by HTTP. The full implementation of
http_timestamp/2
as available from library(http/http_header) is here.
http_timestamp(Time, Atom) :-
stamp_date_time(Time, Date, 'UTC'),
format_time(atom(Atom),
'%a, %d %b %Y %T GMT',
Date, posix).
| Standard | Format string |
| xsd | ’%FT%T%:z’ |
| ISO8601 | ’%FT%T%z’ |
| RFC822 | ’%a, %d %b %Y %T %z’ |
| RFC1123 | ’%a, %d %b %Y %T GMT’ |
posix, which
currently only modifies the behaviour of the a, A, b
and B format specifiers. The predicate is used to be able
to emit POSIX locale week and month names for emitting standardised
time-stamps such as RFC1123.parse_time(Text, _Format, Stamp). See parse_time/3.
| Name | Example |
| rfc_1123 | Fri, 08 Dec 2006 15:29:44
GMT |
Fri, 08 Dec 2006 15:29:44 +0000 | |
| iso_8601 | 2006-12-08T17:29:44+02:00 |
20061208T172944+0200 | |
2006-12-08T15:29Z | |
2006-12-08 | |
20061208 | |
2006-12 | |
2006-W49-5 | |
2006-342 |
Date = date(Year,Month,Day).
Days of the week are numbered from one to seven: Monday = 1, Tuesday =
2, ... , Sunday = 7.
The Windows executable swipl-win.exe console has a number of predicates to control the appearance of the console. Being totally non-portable, we do not advise using it for your own application, but use XPCE or another portable GUI platform instead. We give the predicates for reference here.
win_window_title for
consistent naming.bottom, top, topmost and notopmost.
Topmost windows are displayed above all other windows.true, show the window, if false hide the
window.foreground, background, selection_foreground
or
selection_background. RGB is a term
rgb(Red,Green,Blue) where the components are values between
0 and 255. The defaults are established using the Windows API
GetSysColor().&
is underlined and defines the associated accelerator key. Before
is the label before which this one must be inserted. Using -
win_insert_menu('&Application', '&Help')
-