Types and modes

6.2 Types and modes

The templates part defines, for each argument of the concerned built-in predicate, its mode and type. The mode specifies whether or not the argument must be instantiated when the built-in predicate is called. The mode is encoded with a symbol just before the type. Possible modes are:

+: the argument must be instantiated.
-: the argument must be a variable (will be instantiated if the built-in predicate succeeds).
?: the argument can be instantiated or a variable.

The type of an argument is defined by the following table:

Type Description

TYPE_list a list whose the type of each element is TYPE

TYPE1_or_TYPE2 a term whose type is either TYPE1 or TYPE2

atom an atom

atom_property an atom property (section 8.19.11)

boolean the atom true or false

byte an integer ≥ 0 and ≤ 255

callable_term an atom or a compound term

character a single character atom

character_code an integer ≥ 1 and ≤ 255

clause a clause (fact or rule)

close_option a close option (section 8.10.7)

compound_term a compound term

evaluable an arithmetic expression (section 8.6.1)

fd_bool_evaluable a boolean FD expression (section 9.7.1)

fd_labeling_option an FD labeling option (section 9.9.1)

fd_evaluable an arithmetic FD expression (section 9.6.1)

fd_variable an FD variable

flag a Prolog flag (section 8.22.1)

float a floating point number

head a head of a clause (atom or compound term)

integer an integer

in_byte an integer ≥ 0 and ≤ 255 or -1 (for the end-of-file)

in_character a single character atom or the atom end_of_file (for the end-of-file)

in_character_code an integer ≥ 1 and ≤ 255 or -1 (for the end-of-file)

io_mode an atom in: read, write or append

list the empty list [] or a non-empty list [_|_]

nonvar any term that is not a variable

number an integer or a floating point number

operator_specifier an operator specifier (section 8.14.10)

os_file_property an operating system file property (section 8.27.11)

predicate_indicator a term Name/Arity where Name is an atom and Arity an integer ≥ 0. A callable term can be given if the strict_iso Prolog flag is switched off (section 8.22.1)

predicate_property a predicate property (section 8.8.2)

read_option a read option (section 8.14.1)

socket_address a term of the form ’AF_UNIX’(A) or ’AF_INET’(A,N) where A is an atom and N an integer

socket_domain an atom in: ’AF_UNIX’ or ’AF_INET’

source_sink an atom identifying a source or a sink

stream a stream-term: a term of the form ’$stream’(N) where N is an integer ≥ 0

stream_option a stream option (section 8.10.6)

stream_or_alias a stream-term or an alias (atom)

stream_position a stream position: a term ’$stream_position’(I1, I2, I3, I4) where I1, I2, I3 and I4 are integers

stream_property a stream property (section 8.10.10)

stream_seek_method an atom in: bof, current or eof

term any term

var_binding_option a variable binding option (section 8.5.3)

write_option a write option (section 8.14.6)

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