guile-json is a JSON module for Guile. It supports parsing and building JSON documents according to the http://json.org specification. These are the main features:

• Strictly complies to http://json.org specification.
• Build JSON documents programmatically via macros.
• Basic unicode support for strings.
• Allows JSON pretty printing.

guile-json is freely available for download under the terms of the GNU Lesser General Public License version 3 (LGPLv3+).

Download the latest tarball and untar it:

• guile-json-0.5.0.tar.gz

Then, run the typical sequence:

$ ./configure --prefix=<guile-prefix>
$ make
$ sudo make install

Where <guile-prefix> should preferably be the same as your system Guile installation directory (e.g. /usr).

If everything installed successfully you should be up and running:

$ guile
scheme@(guile-user)> (use-modules (json))
scheme@(guile-user)> (scm->json (json (array 1 2 3)))
[1, 2, 3]

It might be that you installed guile-json somewhere differently than your system’s Guile. If so, you need to indicate Guile where to find guile-json, for example:

$ GUILE_LOAD_PATH=/usr/local/share/guile/site guile

A pkg-list.scm file is also provided for users of the Guildhall/Dorodango packaging system.

guile-json provides a few procedures to parse and build a JSON document. A JSON document is transformed into or from native Guile values according to the following table:

To start using guile-json procedures and macros you first need to load the module:

scheme@(guile-user)> (use-modules (json))

• (json->scm #:optional port) : Reads a JSON document from the given port, or from the current input port if none is given.
  • port : is optional, it defaults to the current input port.
• (json-string->scm str) : Reads a JSON document from the given string.
• (scm->json native #:optional port #:key escape pretty) : Creates a JSON document from the given native Guile value. The JSON document is written into the given port, or to the current output port if non is given.
  • port : it defaults to the current output port.
  • escape : if true, the slash (/ solidus) character will be escaped.
  • pretty : if true, the JSON document will be pretty printed.
• (scm->json-string native #:key escape pretty) : Creates a JSON document from the given native Guile value into a string.
  • escape : if true, the slash (/ solidus) character will be escaped.
  • pretty : if true, the JSON document will be pretty printed.

A json-invalid exception is thrown if an error is found during the JSON parsing. Since version 0.2.0, the json-invalid exception has a single parser argument (see predicate and accessors below). The line or column where the error occured can be easily obtained from the parser port (calling port-line or port-column on the port).

• (json-parser? parser) : Tells whether the given argument is a JSON parser record type.
• (json-parser-port parser) : Get the port that the parser was reading from.

It is also possible to build JSON documents programmatically using the main json macro (and object and array). Here are some examples:

• Build the string “hello world”:

  scheme@(guile-user)> (scm->json (json "hello world"))
  "hello world"
      

• Build the [1, 2, 3] array:

  scheme@(guile-user)> (scm->json (json (array 1 2 3)))
  [1, 2, 3]
      

• Build the [1, 2, 3, 4] array using unquote-splicing:

  scheme@(guile-user)> (define values '(2 3))
  scheme@(guile-user)> (scm->json (json (array 1 ,@values 4)))
  [1, 2, 3, 4]
      

• Build the object { “project” : “foo”, “author” : “bar” }:

  scheme@(guile-user)> (scm->json (json (object ("project" "foo")
                                                ("author" "bar"))))
  {"author" : "bar", "project" : "foo"}
      

• Build the object { “values” : [ 234, 98.56 ] }:

  scheme@(guile-user)> (scm->json (json (object ("values" (array 234 98.56)))))
  {"values" : [234, 98.56]}
      

• Build the object { “values” : [ 234, 98.56 ] } again, this time using a variable:

  scheme@(guile-user)> (define values '(234 98.56))
  scheme@(guile-user)> (scm->json (json (object ("values" ,values))))
  {"values" : [1, 2, 3]}