Prolog state

8.22 Prolog state

8.22.1 set_prolog_flag/2

Templates

: set_prolog_flag(+flag, +term)

Description

set_prolog_flag(Flag, Value) sets the value of the Prolog flag Flag to Value.

Prolog flags: a Prolog flag is an atom which is associated with a value that is either implementation defined or defined by the user. Each flag has a permitted range of values; any other value is a domain_error. The following two tables present available flags, the possible values, a description and if they are ISO or an extension. The first table presents unchangeable flags while the second one the changeable flags. For flags whose default values is machine independent, this value is underlined.

Unchangeable flags:

Flag	Values	Description	ISO
prolog_name	an atom	name of the Prolog system	N
prolog_version	an atom	version number of the Prolog system	N
prolog_date	an atom	date of the Prolog system	N
prolog_copyright	an atom	copyright message of the Prolog system	N
dialect	an atom	fixed to gprolog	N
version	an integer	Major * 10000 + Minor * 100 + Patch	N
version_data	a structure	gprolog(Major,Minor,Patch,Extra)	N
bounded	true / false	are integers bounded ?	Y
max_integer	an integer	greatest integer	Y
min_integer	an integer	smallest integer	Y
integer_rounding_function	toward_zero down	rnd(X) = integer part of X rnd(X) = ⌊X⌋ (section 8.6.1)	Y
max_arity	an integer	maximum arity for compound terms (255)	Y
max_atom	an integer	maximum number of atoms	N
max_unget	an integer	maximum number of successive ungets	N
home	an atom	GNU Prolog home directory	N
host_os	an atom	Operating System identifier	N
host_vendor	an atom	Operating System vendor	N
host_cpu	an atom	processor identifier	N
host	an atom	a combination of the OS-vendor-cpu	N
arch	an atom	a combination of the OS-cpu	N
address_bits	an integer	address size of the machine (32 or 64)	N
unix	on/off	is the architecture an Unix-like OS ?	N
compiled_at	an atom	compilation date using __DATE__ and __TIME__ C compiler macros	N
c_cc	an atom	C compiler used to compile GNU Prolog (gcc, cc, clang, cl,...)	N
c_cc_version_data	a structure	c_cc(Major,Minor,Patch,Extra)	N
c_cflags	an atom	CFLAGS used to compile GNU Prolog	N
c_ldflags	an atom	LDFLAGS used to compile GNU Prolog	N
argv	a list of atoms	list of command-line arguments	N

Changeable flags:

Flag	Values	Description	ISO
char_conversion	on / off	is character conversion activated ?	Y
singleton_warning	on / off	warn about named singleton variables ?	N
suspicious_warning	on / off	warn about suspicious predicate ?	N
multifile_warning	on / off	warn about unsupported multifile directive ?	N
strict_iso	on / off	strict ISO behavior ?	N
debug	on / off	is the debugger activated ?	Y
double_quotes	atom chars codes atom_no_escape chars_no_escape codes_no_escape	a double quoted constant is returned as: an atom a list of characters a list of character codes as atom but ignore escape sequences as chars but ignore escape sequences as code but ignore escape sequences	Y N
back_quotes	atom chars codes atom_no_escape chars_no_escape codes_no_escape	a back quoted constant is returned as: an atom a list of characters a list of character codes as atom but ignore escape sequences as chars but ignore escape sequences as code but ignore escape sequences	N
unknown	error warning fail	a predicate calls an unknown procedure: an existence_error is raised a message is displayed then fails quietly fails	Y
syntax_error	error warning fail	a predicate causes a syntax error: a syntax_error is raised a message is displayed then fails quietly fails	N
os_error	error warning fail	a predicate causes an O.S. error: a system_error is raised a message is displayed then fails quietly fails	N

The strict_iso flag is introduced to allow a compatibility with other Prolog systems. When turned off the following relaxations apply:

built-in predicates are found by current_predicate/1 (section 8.8.1).
the term parser (read/1 and friends) is more indulgent, e.g. 0’’ is accepted and returns 39, the escape sequence \s (space) and \e (escape) are accepted.
the following arithmetic rounding functions: ceiling, floor, round, truncate also accept integers (section 8.6.1).

Errors


Flag is a variable		instantiation_error

Value is a variable		instantiation_error

Flag is neither a variable nor an atom		type_error(atom, Flag)

Flag is an atom but not a valid flag		domain_error(prolog_flag, Flag)

Value is inappropriate for Flag		domain_error(flag_value, Flag+Value)

Value is appropriate for Flag but flag Flag is not modifiable		permission_error(modify, flag, Flag)

Portability

ISO predicate. All ISO flags are implemented.

8.22.2 current_prolog_flag/2

Templates

: current_prolog_flag(?flag, ?term)

Description

current_prolog_flag(Flag, Value) succeeds if there exists a Prolog flag that unifies with Flag and whose value unifies with Value. This predicate is re-executable on backtracking.

Errors


Flag is neither a variable nor an atom		type_error(atom, Flag)

Flag is an atom but not a valid flag		domain_error(prolog_flag, Flag)

Portability

ISO predicate.

8.22.3 set_bip_name/2

Templates

: set_bip_name(+atom, +arity)

Description

set_bip_name(Functor, Arity) initializes the context of the error (section 6.3.1) with Functor and Arity (if Arity < 0 only Functor is significant).

Errors


Functor is a variable		instantiation_error

Arity is a variable		instantiation_error

Functor is neither a variable nor an atom		type_error(atom, Functor)

Arity is neither a variable nor an integer		type_error(integer, Arity)

Portability

GNU Prolog predicate.

8.22.4 current_bip_name/2

Templates

: current_bip_name(?atom, ?arity)

Description

current_bip_name(Functor, Arity) succeeds if Functor and Arity correspond to the context of the error (section 6.3.1) (if Arity < 0 only Functor is significant).

Errors


Functor is neither a variable nor an atom		type_error(atom, Functor)

Arity is neither a variable nor an integer		type_error(integer, Arity)

Portability

GNU Prolog predicate.

8.22.5 write_pl_state_file/1, read_pl_state_file/1

Templates

: write_pl_state_file(+source_sink)
read_pl_state_file(+source_sink)

Description

write_pl_state_file(FileName) writes onto FileName all information that influences the parsing of a term (section 8.14). This allows a sub-process written in Prolog to read this file and then process any Prolog term as done by the parent process. This file can also be passed as argument of the --pl-state option when invoking gplc (section 4.4.3). More precisely the following elements are saved:

all operator definitions (section 8.14.10).
the character conversion table (section 8.14.12).
the value of char_conversion, double_quotes, back_quotes, singleton_warning, suspicious_warning and multifile_warning Prolog flags (section 8.22.1).

read_pl_state_file(FileName) reads (restores) from FileName all information previously saved by write_pl_state_file/1.

Errors


FileName is a variable		instantiation_error

FileName is neither a variable nor an atom		type_error(atom, FileName)

an operating system error occurs and the value of the os_error Prolog flag is error (section 8.22.1)		system_error(atom explaining the error)

Portability

GNU Prolog predicate.