Next: ref-lps-lco, Previous: ref-lps-apf, Up: ref-lps [Contents][Index]
Certain aspects of the state of the program are accessible as values of the global Prolog flags. Some of these flags are read-only and correspond to implementation defined properties and exist to aid portability. Others can be set and impact the behavior of certain built-in predicates.
The flags are accessed by the built-in predicates prolog_flag/[2,3]
,
current_prolog_flag/2
, and set_prolog_flag/2
.
Please note: Prolog flags are global, as opposed to being local to the current module, Prolog text, or otherwise.
The possible Prolog flag names and values are listed below. Flags
annotated ISO are prescribed by the ISO standard. Flags
annotated volatile are not saved by save_program/[1,2]
.
Flags annotated read-only are read-only:
agc_margin
An integer Margin. The atoms will be garbage collected when Margin new atoms have been created since the last atom garbage collection. Initially 10000.
argv volatile
The value is a list of atoms of the program arguments supplied when the current SICStus Prolog process was started. For example, if SICStus Prolog were invoked with:
% sicstus -- hello world 2001
then the value will be [hello,world,'2001']
.
Setting the value can be useful when writing test cases for code that expects to be run with command line parameters.
bounded read-only,volatile,ISO
One of the flags defining the integer type. For
SICStus, its value is false
, indicating that the domain of
integers is practically unbounded.
char_conversion volatile,ISO
If this flag is on
, then unquoted characters in terms and
programs read in will be converted, as specified by previous
invocations of char_conversion/2
. If the flag is off
, then no
conversion will take place. The default value is on
.
compiling
Governs the mode in which compile/1
operate (see ref-lod).
compactcode
Compilation produces byte-coded abstract instructions (the default).
debugcode
Compiling is replaced by consulting.
debugging volatile
Corresponds to the predicates debug/0
, nodebug/0
,
trace/0
, notrace/0
, zip/0
, nozip/0
. The
flag describes the mode the debugger is in, or is required to be
switched to:
trace
Trace mode (the debugger is creeping).
debug
Debug mode (the debugger is leaping).
zip
Zip mode (the debugger is zipping).
off
The debugger is switched off (the default).
debug volatile,ISO
The flag debug
, prescribed by the ISO Prolog standard, is a
simplified form of the debugging
flag:
off ISO
The debugger is switched off (the default).
on ISO
The debugger is switched on (to trace mode, if previously switched off).
profiling since release 4.2
This flag describes the mode the execution profiler (see Execution Profiling) is in, or is required to be switched to:
off
The profiler is switched off (the default).
on
The profiler is switched on.
(The flags profiling
, debugging
and debug
have no effect in
runtime systems.)
double_quotes volatile,ISO
Governs the interpretation of double quoted strings (see ref-syn-cpt-sli):
codes ISO
Code list comprising the string. The default.
chars ISO
Char list comprising the string.
atom ISO
The atom composed of the same characters as the string.
quoted_charset
This flag is relevant when quoted(true)
holds when writing terms.
Its value should be one of the atoms:
portable
Atoms and functors are written using character codes less than 128 only, i.e. using the 7-bit subset of the ISO-8859-1 (Latin 1) character set (see ref-syn-syn-tok).
prolog
Atoms and functors are written using a character set that can be read
back by read/[1,2]
. This is a subset of Unicode that includes all
of ISO-8859-1 (Latin 1) as well as some additional characters.
This character set may grow but not shrink in subsequent releases. This ensures that future releases can always read a term written by an older release.
Note that the character set supported by the stream is not taken into
account. You can use portable
instead of prolog
if the
stream does not support Unicode.
debugger_print_options
The value is a list of options for write_term/3
(see ref-iou-tou-wrt), to be used in the debugger’s messages. The initial
value is
[quoted(true),numbervars(true),portrayed(true),max_depth(10)]
.
dialect since release 4.1,read-only
The value of this flag is sicstus
. It is useful for
distinguishing between Prolog implementations.
Also see the Prolog flag version_data
, below.
discontiguous_warnings volatile
on
or off
. Enable or disable warning messages when
clauses are not together in source files. Initially on
in
development systems, off
in runtime systems.
fileerrors
on
or off
. Enables or disables raising of file error
exceptions. Initially on
(enabled).
gc
on
or off
. Enables or disables garbage collection
of the global stack. Initially on
(enabled).
gc_margin
Margin: At least Margin kilobytes of free global stack space are guaranteed to exist after a garbage collection. Also, no garbage collection is attempted if the global stack has grown less than Margin kilobytes since the last garbage collection. Initially 1000.
gc_trace
Governs global stack garbage collection trace messages.
verbose
Turn on verbose tracing of garbage collection.
terse
Turn on terse tracing of garbage collection.
off
Turn off tracing of garbage collection (the default).
host_type read-only,volatile
The value is an atom identifying the platform
on which SICStus was compiled, such as 'x86-linux-glibc2.1'
.
informational volatile
on
or off
. Enables or disables the printing of
informational messages. Initially on
(printing enabled) in
development systems, unless the --noinfo command line option
was used; off
(printing disabled) in runtime systems.
integer_rounding_function read-only,volatile,ISO
One of the flags defining the integer type. In
SICStus Prolog its value is toward_zero
, indicating that the
integer division ((//)/2
) and integer remainder (rem/2
)
arithmetic functions use rounding toward zero; see ref-ari.
legacy_char_classification since release 4.0.3,volatile
on
or off
. When enabled, most legal Unicode codepoints
above 255 are treated as lowercase characters when reading Prolog
terms. This improves compatibility with earlier versions of SICStus
Prolog and makes it possible to use full Unicode, e.g. Chinese characters, in
unquoted atoms as well as variable names, ref-syn-syn-tok.
Initially off
(disabled).
Setting this flag affects the read_term/[2,3]
option
singletons/1
; see mpg-ref-read_term. It also affects the
style warning for singleton variables; see the description of the
single_var_warnings
in The Load Predicates.
max_arity read-only,volatile,ISO
Specifies the maximum arity allowed for a compound term. In SICStus Prolog this is 255.
max_integer read-only,volatile,ISO
Specifies the largest possible integer value. As in
SICStus Prolog the range of integers in not bounded,
prolog_flag/[2,3]
and current_prolog_flag/2
will fail when
accessing this flag.
max_tagged_integer since release 4.1,read-only,volatile
The largest small integer, i.e. integers larger than this are
less efficient to manipulate and are not available in library(clpfd)
.
min_integer read-only,volatile,ISO
Specifies the smallest possible integer value. As in
SICStus Prolog the range of integers in not bounded,
prolog_flag/[2,3]
and current_prolog_flag/2
will fail, when
accessing this flag.
min_tagged_integer since release 4.1,read-only,volatile
The smallest small integer, i.e. integers smaller than this are
less efficient to manipulate and are not available in library(clpfd)
.
os_data since release 4.1,read-only,volatile
The value is a term os(Family,Name,Extra)
describing the
operating system on which this SICStus process is running, i.e. it is
the runtime version of the platform_data
flag, below.
Family has the same value and meaning as for the
platform_data
flag, below.
On UNIX-like systems the Name is the lower case value
sysname
returned from uname(3)
at runtime, i.e. the same as from
the command uname -s
. On all supported versions of Microsoft
Windows this is win32nt
.
Extra
is a list of extra information. Entries may be added to
this list without prior notice.
Currently, at least up to release 4.2.3, the Family and Name
for the platform_data
and os_data
flags happens to be the
same but this may change in the unlikely case that the operating system
starts to return something new. For this reason it is probably better to
use platform_data
than os_data
in most cases.
The
Extra
value for os_data
may differ from its
platform_data
counterpart in order to accurately describe the
running operating system.
platform_data since release 4.1,read-only,volatile
The value is a term platform(Family,Name,Extra)
describing the
operating system platform for which this version of SICStus was built.
Family describes the family or class of operating
system. Currently documented values are unix
, for UNIX-like systems like
Linux, OS X, Solaris and Android; and
windows
for all supported versions of Microsoft Windows. You should not assume
that these are the only two possibilities.
Name describes the name of the operating system. On UNIX-like
systems this correspond to the (lower case) output from uname
-s
. Currently documented values are linux
, darwin
,
android
and win32nt
.
Note that this implies that some operating systems may have unexpected
names. In particular the name for Apple OS X is darwin
and for
64-bit versions of SICStus on Microsoft Windows it is win32nt
.
Extra
is bound to a list of extra information. Entries may be
added to this list without prior notice.
redefine_warnings
Enable or disable warning messages when:
The possible values are:
on
The default in development systems. The user is queried about what to do in each case.
off
The default in runtime systems, but note that this flag is not volatile. Redefinitions are performed silently, as if the user had accepted them.
reject since release 4.0.3
Redefinitions are refused silently, as if the user had rejected them.
proceed since release 4.0.3
Redefinitions are performed, and warnings are issued.
suppress since release 4.0.3
Redefinitions are refused, and warnings are issued.
single_var_warnings volatile
on
or off
. Enable or disable warning messages when a
sentence (see ref-syn-syn-sen) containing variables not
beginning with ‘_’ occurring once only is compiled or consulted.
Initially on
in development systems, off
in runtime
systems.
source_info volatile
emacs
or on
or off
. If not off
while
source code is being loaded, then information about line numbers
and file names are stored with the loaded code. If the value is
on
while debugging, then this information is used to print the
source code location while prompting for a debugger command. If
the value is on
while printing an uncaught error exception
message, then the information is used to print the source code location
of the culprit goal or one of its ancestors, as far as it
can be determined. If the value is emacs
in any of these cases, then
the appropriate line of code is instead highlighted, and no extra text
is printed. The value is off
initially, and that is its only
available value in runtime systems.
syntax_errors
Controls what action is taken upon syntax errors in
read/[1,2]
.
dec10
The syntax error is reported and the read is repeated.
error
An exception is raised. See ref-ere. (the default).
fail
The syntax error is reported and the read fails.
quiet
The read quietly fails.
system_type read-only,volatile
The value is development
in development
systems and runtime
in runtime systems.
title
The window title. The default value is the same as the boot message ‘SICStus 4.9.0 … Licensed to SICS’. It is currently only used as the window title on the Windows platform.
toplevel_print_options
The value is a list of options for write_term/3
(see ref-iou-tou-wrt), to be used when the top level displays
variable bindings and answer constraints. It is also used when
messages are displayed. The initial value is
[quoted(true),numbervars(true),portrayed(true),max_depth(10)]
.
typein_module
Permitted values are atoms. Controls the current type-in module
(see ref-mod-tyi). Corresponds to the predicate set_module/1
.
unknown ISO
The system can optionally catch calls to predicates that have no
definition. First, the user defined predicate
user:unknown_predicate_handler/3
(see ref-ere) is called. If
undefined or if the call fails, then the action is governed by the state of
the this flag, which can be:
trace
Causes calls to undefined predicates to be reported and the debugger to be entered at the earliest opportunity. Not available in runtime systems.
error ISO
Causes calls to such predicates to raise an exception (the default). See ref-ere.
warning ISO
Causes calls to such predicates to display a warning message and then fail.
fail ISO
Causes calls to such predicates to fail.
user_input volatile
Permitted values are any stream opened for reading. Controls
which stream is referenced by user_input
and
SP_stdin
. It is initially set to a stream connected to UNIX
stdin
.
user_output volatile
Permitted values are any stream opened for writing.
Controls which stream is referenced by
user_output
and SP_stdout
. It is initially set to a stream
connected to UNIX stdout
.
user_error volatile
Permitted values are any stream opened for writing.
Controls which stream is referenced by
user_error
and SP_stderr
. It is initially set to a stream
connected to UNIX stderr
.
version read-only,volatile
The value is an atom containing the banner text
displayed on startup, such as
'SICStus 4.1.0 (i386-darwin-9.8.0): Wed Oct 14 14:43:58 CEST 2009'
.
Also see the Prolog flag version_data
, below.
version_data since release 4.1,read-only,volatile
The value is a term sicstus(Major,Minor,Revision,Beta,Extra)
with
integer major, minor, revision, and beta version.
Extra
is bound to a list of extra information. Entries may be
added to this list without prior notice.
Also see the Prolog flag dialect
, above.
You can use prolog_flag/2
to enumerate all the FlagNames that
the system currently understands, together with their current values.
Use prolog_flag/2
to make queries, prolog_flag/3
to
make changes.