json.md

Supporting JSON {#jsonsupport}

From http://json.org, " JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language."

Although JSON is nowadays used a lot outside the context of web applications, SWI-Prolog's support for JSON started life as part of the HTTP package. SWI-Prolog supports two Prolog representations for JSON terms. The first and oldest map JSON objects to a term json(PropertyList) and use the @ functor to disambiguate e.g. null from the string "null", leading to @(null). As of SWI-Prolog version 7, JSON objects may be represented using dict objects and JSON strings using Prolog strings. Predicates following this convention are suffixed with _dict, e.g. json_read_dict/2. For example, given the JSON document

{ "name": "Bob", "children": ["Mary", "John"], "age":42, "married": true }

we get either (using json_read/2):

json([name='Bob', children=['Mary', 'John'], age=42, married= @(true)]).

or (using json_read_dict/2):

_{age:42, children:["Mary", "John"], married:true, name:"Bob"}

The SWI-Prolog JSON interface consists of three libraries:

* library(http/json) provides support for the core JSON object
  serialization and parsing.
* library(http/json_convert) converts between the primary
  representation of JSON terms in Prolog and more application
  oriented Prolog terms.  E.g. point(X,Y) vs. object([x=X,y=Y]).
* library(http/http_json) hooks the conversion libraries into
  the HTTP client and server libraries.

[[library(http/json)]]
[[library(http/json_convert)]]
[[library(http/http_json)]]