ignore (ignore the attribute), dots
(write the attributes as {...}), write (simply
hand the attributes recursively to write_term/2)
and portray (hand the attributes to attr_portray_hook/2).string causes string
objects to be printed between back quotes and symbol_char
causes the backquote to be printed unquoted. In all other cases the
backquote is printed as a quoted atom.true (default), write {}(X) as {X}.
See also
dotlists and ignore_ops.portray,
portray/1
is called for each blob encountered. See section
12.4.10.true and quoted(true) is active, special
characters in quoted atoms and strings are emitted as ISO escape
sequences. Default is taken from the reference module (see below).true and character_escapes(true) and
quoted(true) are active escapted characters are written
using
\uXXXX or \UXXXXXXXX syntax. The default
depends on the Prolog flag character_escapes_unicodetrue (default), cyclic terms are written as
@(Template, Substitutions), where Substitutions
is a list
Var = Value. If cycles is false,
max_depth is not given, and Term is cyclic, write_term/2
raises a domain_error.108The
cycles option and the cyclic term representation using the @-term are
copied from SICStus Prolog. However, the default in SICStus is set to false
and SICStus writes an infinite term if not protected by, e.g., the depth_limit
option. See also the cycles option in
read_term/2.true (default false), write lists using the
dotted term notation rather than the list notation.109Copied
from ECLiPSe. Note that as of version 7, the list
constructor is
'[|]'. Using dotlists(true), write_term/2
writes a list using‘.’as constructor. This is intended for
communication with programs such as other Prolog systems, that rely on
this notation. See also the option no_lists(true) to use
the actual SWI-Prolog list functor.true (default false), add a fullstop token
to the output. The dot is preceded by a space if needed and followed by
a space (default) or newline if the nl(true) option is also
given.110Compatible with ECLiPSeformat(Atom, [Float]). The default is ~h.
This option is compatible with SICStus. See format/2
for valid format specifiers and the
integer_format option for additional comments.true, the generic term representation (<functor>(<args>
... )) will be used for all terms. Otherwise (default), operators will
be used where appropriate.111In
traditional systems this flag also stops the syntactic sugar notation
for lists and brace terms. In SWI-Prolog, these are controlled by the
separate options dotlists and brace_terms.format(Atom, [Int]). The default is ~d.
This allows to print integers using an alternative radix, using
e.g. ~16r or 0x~16r or to use digit grouping
using e.g. ~D. Note that the user is reponsible to provide
a format that produces valid Prolog syntax if the term must be readable
by Prolog. The format must accept exactly one argument. If that is not
satisfied, printing an integer results in an exception. See format/2
for for valid format specifiers.
?- write_term(a(s(s(s(s(0)))), [a,b,c,d,e,f]),
[max_depth(3)]).
a(s(s(...)), [a, b|...])
true.
Used by the top level and debugger to limit screen output. See also the Prolog flags answer_write_options and debugger_write_options.
user). This defines
the default value for the character_escapes
option as well as the operator definitions to use. If Module
does not exist it is
not created and the user module is used. See also op/3
and read_term/2,
providing the same option.fullstop option.dotlists(true),
but uses the SWI-Prolog list functor, which is by default '[|]'
instead of the ISO Prolog '.'. Used by display/1.true, terms of the format $VAR(N), where N
is an integer that fits in 64-bit,112Larger
integers are ignored. As no term that fits into memory can have that
many variables, this is not a restriction. will be written
as a variable name. For N in 0..25 it emits A..Z. For higher
numbers it emits An..Zn, where
n is N//26. For negative numbers it emits S_N,
which is used for representing shared sub-terms and cyclic terms.
If N is an atom that is syntactically a valid variable it is written without quotes. This extension allows for writing variables with user-provided names.
The default for this flag is false unless the
portrayed option is enabled. See also numbervars/3
and the option variable_names.
true (default false), do not reset the
logic that inserts extra spaces that separate tokens where needed. This
is intended to solve the problems with the code below. Calling write_value(.)
writes .., which cannot be read. By adding partial(true)
to the option list, it correctly emits . .. Similar
problems appear when emitting operators using multiple calls to write_term/3.
write_value(Value) :-
write_term(Value, [partial(true)]),
write('.'), nl.
In addition, if the priority is not 1200 or 999 this assumes we are printing an operant of an operator. If Term is an atom that is also an operator it will always be embraced.113If the priority is 1200 it is assumed to be a toplevel term and if the priority is 999 it is assumed to be a list element or argument of a compound term.
portrayed(Bool). Deprecated.portray(true), but calls Goal rather
than the predefined hook portray/1. Goal
is called through call/3,
where the first argument is Goal, the second is the term to
be printed and the 3rd argument is the current write option list. The
write option list is copied from the write_term call, but the list is
guaranteed to hold an option priority that reflects the
current priority.true, the hook portray/1
is called before printing a term that is not a variable. If portray/1
succeeds, the term is considered printed. See also print/1.
The default is false. This option is an extension to the
ISO write_term options. If this option is set, the numbervars
option defaults to true.
format('~w = ', [VarName]),
write_term(Value, [quoted(true), priority(699)])
true, atoms and strings that need quotes will be quoted.
The default is false. If character_escapes
is
true (default) characters in the quoted atom or string are
escaped using backslash (\\u0020)
are escaped. For those characters for which an ISO Prolog single
character escape, e.g.,
\t is defined, this is used. Otherwise the output depends
on the option character_escapes_unicode. If this flag
applies(default) the widely accepted \uXXXX or \UXXXXXXXX
is used. Otherwise the ISO Prolog \x<hex>\ syntax is
used.standard, adding only space
where needed for proper tokenization by read_term/3.
Currently, the only other value is next_argument, adding a
space after a comma used to separate arguments in a term or list.
The implementation binds the variables from List to a term
'$VAR'(Name). Like write_canonical/1,
terms that where already bound to '$VAR'(X)
before write_term/2
are printed normally, unless the option numbervars(true) is
also provided. If the option numbervars(true) is used, the
user is responsible for avoiding collisions between assigned names and
numbered names. See also the variable_names option of
read_term/2.
Possible variable attributes (see section 8.1) are ignored. In most cases one should use copy_term/3 to obtain a copy that is free of attributed variables and handle the associated constraints as appropriate for the use-case.