SWI-Prolog -- json

Availability::- use_module(library(http/json)).

[det]json_write(+Stream, +Term)

[det]json_write(+Stream, +Term, +Options)

Write a JSON term to Stream. The JSON object is of the same format as produced by json_read/2, though we allow for some more flexibility with regard to pairs in objects. All of Name=Value, Name-Value and Name(Value) produce the same output.

Values can be of the form #(Term), which causes Term to be stringified if it is not an atom or string. Stringification is based on term_string/2.

Rational numbers are emitted as floating point numbers. The hook json_write_hook/4 can be used to realize domain specific alternatives.

The version 7 dict type is supported as well. Optionally, if the dict has a tag, a property "type":"tag" can be added to the object. This behaviour can be controlled using the tag option (see below). For example:

?- json_write(current_output, point{x:1,y:2}).
{
  "x":1,
  "y":2
}

?- json_write(current_output, point{x:1,y:2}, [tag(type)]).
{
  "type":"point",
  "x":1,
  "y":2
}

In addition to the options recognised by json_read/3, we process the following options are recognised:

width(+Width): Width in which we try to format the result. Too long lines switch from horizontal to vertical layout for better readability. If performance is critical and human readability is not an issue use Width = 0, which causes a single-line output.
step(+Step): Indentation increnment for next level. Default is 2.
tab(+TabDistance): Distance between tab-stops. If equal to Step, layout is generated with one tab per level.
serialize_unknown(+Boolean): If true (default false), serialize unknown terms and print them as a JSON string. The default raises a type error. Note that this option only makes sense if you can guarantee that the passed value is not an otherwise valid Prolog reporesentation of a Prolog term.

If a string is emitted, the sequence </ is emitted as <\/. This is valid JSON syntax which ensures that JSON objects can be safely embedded into an HTML <script> element.