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<clix:documentation xmlns:clix="http://bknr.net/clixdoc"
                    xmlns="http://www.w3.org/1999/xhtml">

  <clix:title>YASON - A JSON encoder/decoder for Common Lisp</clix:title>

  <clix:short-description>
    YASON is a JSON encoding and decoding library for Common Lisp.  It
    provides for functions to read JSON strings into Lisp data
    structures and for serializing Lisp data structures as JSON
    strings.
  </clix:short-description>

  <clix:abstract>
    YASON is a Common Lisp library for encoding and decoding data in
    the <a href="http://json.org/">JSON</a> interchange format.  JSON
    is used as a lightweight alternative to XML.  YASON has the sole
    purpose of encoding and decoding data and does not impose any
    object model on the Common Lisp application that uses it.
  </clix:abstract>

  <clix:contents/>

  <clix:chapter name="intro" title="Introduction">
    <p>
      <a href="http://json.org/">JSON</a> is an established
      alternative to XML as a data interchange format for web
      applications.  YASON implements reading and writing of JSON
      formatted data in Common Lisp.  It does not attempt to provide a
      mapping between CLOS objects and YASON, but can be used to
      implement such mappings.
    </p>
    <p>
      <a href="http://common-lisp.net/project/cl-json/">CL-JSON</a> is
      another Common Lisp package that can be used to work with JSON
      encoded data.  It takes a more integrated approach, providing
      for library internal mappings between JSON objects and CLOS
      objects.  YASON was created as a lightweight, documented
      alternative with a minimalistic approach and extensibilty.
    </p>
  </clix:chapter>

  <clix:chapter name="install" title="Download and Installation">
    <p>
      YASON has its permanent home at <a
      href="https://github.com/hanshuebner/yason/">GitHub</a>.
      It can be obtained by downloading the <a
      href="https://github.com/downloads/hanshuebner/yason/yason.tar.gz">release
      tarball</a>.  The current release is <clix:current-release/>.
    </p>
    <p>
      You may also check out the current development version from its
      <a href="http://github.com/hanshuebner/yason/">git
      repository</a>.  If you have suggestions regarding YASON, please
      email me at <i>hans.huebner@gmail.com</i>.
    </p>
    <p>
      YASON is written in ANSI Common Lisp.  It depends on UNIT-TEST,
      TRIVIAL-GRAY-STREAMS and ALEXANDRIA open source libraries.  The
      recommended way to install YASON and its dependencies is through
      the excellent <a href="http://www.quicklisp.org/">Quicklisp</a>
      library management system.
    </p>
    <p>
      YASON lives in the <b>:yason</b> package and creates a package
      nickname <b>:json</b>.  Applications will not normally
      <b>:use</b> this package, but rather use qualified names to
      access YASON's symbols.  For that reason, YASON's symbols do not
      contain the string "JSON" themselves.  See below for usage
      samples.
    </p>
  </clix:chapter>
  
  <clix:chapter name="test" title="Running Tests">
    <p>
      To run tests, load the system and run this in the REPL:
      <pre>CL-USER&gt; (asdf:test-system :yason)</pre>
    </p>
  </clix:chapter>

  <clix:chapter name="json-package" title="Using JSON as package name">
    Versions of YASON preceding the v0.6.0 release provided a package
    nickname "JSON" for the "YASON" package.  This made it impossible
    to load both YASON and CL-JSON into the same image, because
    CL-JSON uses the "JSON" package name as well.

    <p>
      As CL-JSON's use of "JSON" as package name has a much longer
      history and loading of both CL-JSON and YASON into the same
      image has become more common, the "JSON" nickname was removed
      from the YASON package with the v0.6.0 release.  Users will need
      to change their applications so that the "JSON" nickname is no
      longer used to refer to the "YASON" package.  It is understood
      that this is a disruptive change, but as there is no
      all-encompassing workaround, this step was felt to be the right
      one to make
    </p>
  </clix:chapter>

  <clix:chapter name="mapping" title="Mapping between JSON and CL datatypes">
    By default, YASON performs the following mappings between JSON and
    CL datatypes:
    <table border="1">
      <thead>
        <tr>
          <th>JSON<br/>datatype</th>
          <th>CL<br/>datatype</th>
          <th>Notes</th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <td>object</td>
          <td>hash-table<br/>:test&#x00A0;#'equal</td>
          <td>
            Keys are strings by default (see
            <clix:ref>*parse-object-key-fn*</clix:ref>).  Set
            <clix:ref>*parse-object-as*</clix:ref> to <b>:alist</b> in
            order to have YASON parse objects as alists or to
            <b>:plist</b> to parse them as plists.  When using plists,
            you probably want to also set
            <clix:ref>*parse-object-key-fn*</clix:ref> to a function
            that interns the object's keys to symbols.
          </td>
        </tr>
        <tr>
          <td>array</td>
          <td>list</td>
          <td>
            Can be changed to read to vectors (see
            <clix:ref>*parse-json-arrays-as-vectors*</clix:ref>).
          </td>
        </tr>
        <tr>
          <td>string</td>
          <td>string</td>
          <td>
            JSON escape characters are recognized upon reading.  Upon
            writing, known escape characters are used, but non-ASCII
            Unicode characters are written as is.
          </td>
        </tr>
        <tr>
          <td>number</td>
          <td>number</td>
          <td>
            Parsed with READ, printed with PRINC.  This is not a
            faithful implementation of the specification.
          </td>
        </tr>
        <tr>
          <td>true</td>
          <td>t</td>
          <td>
	    Can be changed to read as TRUE (see
	    <clix:ref>*parse-json-booleans-as-symbols*</clix:ref>).
	  </td>
        </tr>
        <tr>
          <td>false</td>
          <td>nil</td>
          <td>
	    Can be changed to read as FALSE (see
	    <clix:ref>*parse-json-booleans-as-symbols*</clix:ref>).
	  </td>
        </tr>
        <tr>
          <td>null</td>
          <td>nil</td>
          <td></td>
        </tr>
      </tbody>
    </table>
  </clix:chapter>

  <clix:chapter name="parsing" title="Parsing JSON data">
    <p>
      JSON data is always completely parsed into an equivalent
      in-memory representation.  Upon reading, some translations are
      performed by default to make it easier for the Common Lisp
      program to work with the data; see <clix:ref>mapping</clix:ref>
      for details.  If desired, the parser can be configured to
      preserve the full semantics of the JSON data read.
    </p>

    For example

    <pre>CL-USER> (defvar *json-string* "[{\"foo\":1,\"bar\":[7,8,9]},2,3,4,[5,6,7],true,null]")
*JSON-STRING*
CL-USER&gt; (let* ((result (yason:parse *json-string*)))
           (print result)
           (alexandria:hash-table-plist (first result)))

(#&lt;HASH-TABLE :TEST EQUAL :COUNT 2 {5A4420F1}&gt; 2 3 4 (5 6 7) T NIL)
("bar" (7 8 9) "foo" 1)
CL-USER&gt; (defun maybe-convert-to-keyword (js-name)
           (or (find-symbol (string-upcase js-name) :keyword)
               js-name))
MAYBE-CONVERT-TO-KEYWORD
CL-USER&gt; :FOO ; intern the :FOO keyword
:FOO
CL-USER&gt; (let* ((yason:*parse-json-arrays-as-vectors* t)
                (yason:*parse-json-booleans-as-symbols* t)
                (yason:*parse-object-key-fn* #'maybe-convert-to-keyword)
                (result (yason:parse *json-string*)))
           (print result)
           (alexandria:hash-table-plist (aref result 0)))

#(#&lt;HASH-TABLE :TEST EQUAL :COUNT 2 {59B4EAD1}&gt; 2 3 4 #(5 6 7) YASON:TRUE NIL)
("bar" #(7 8 9) :FOO 1)</pre>

    <p>
      The second example modifies the parser's behaviour so that JSON
      arrays are read as CL vectors, JSON booleans will be read as the
      symbols TRUE and FALSE and JSON object keys will be looked up in
      the <b>:keyword</b> package.  Interning strings coming from an
      external source is not recommended practice.
    </p>

    <clix:subchapter name="parser-dict" title="Parser dictionary">
      <clix:function name="parse">
        <clix:lambda-list>input &amp;key (object-key-fn
        *parse-object-as-key-fn*) (object-as *parse-object-as*)
        (json-arrays-as-vectors *parse-json-arrays-as-vectors*)
        (json-booleans-as-symbols *parse-json-booleans-as-symbols*)
        (json-nulls-as-keyword *parse-json-null-as-keyword*)</clix:lambda-list>
        <clix:returns>object</clix:returns>
        <clix:description>
          Parse <clix:arg>input</clix:arg>, which must be a string or
          a stream, as JSON.  Returns the Lisp representation of the
          JSON structure parsed.
          <p>
            The keyword arguments <clix:arg>object-key-fn</clix:arg>,
            <clix:arg>object-as</clix:arg>,
            <clix:arg>json-arrays-as-vectors</clix:arg>,
            <clix:arg>json-booleans-as-symbols</clix:arg>, and
            <clix:arg>json-null-as-keyword</clix:arg> may be used
            to specify different values for the parsing parameters
            from the current bindings of the respective special
            variables.
          </p>
        </clix:description>
      </clix:function>

      <clix:special-variable name="*parse-json-arrays-as-vectors*">
        <clix:description>
          If set to a true value, JSON arrays will be parsed as
          vectors, not as lists. NIL is the default.
        </clix:description>
      </clix:special-variable>

      <clix:special-variable name="*parse-object-as*">
        <clix:description>
          Can be set to <b>:hash-table</b> to parse objects as hash
          tables, <b>:alist</b> to parse them as alists or
          <b>:plist</b> to parse them as plists.  <b>:hash-table</b>
          is the default.
        </clix:description>
      </clix:special-variable>

      <clix:special-variable name="*parse-json-booleans-as-symbols*">
        <clix:description>
          If set to a true value, JSON booleans will be read as the
          symbols TRUE and FALSE instead of T and NIL, respectively.
          NIL is the default.
        </clix:description>
      </clix:special-variable>

      <clix:special-variable name="*parse-json-null-as-keyword*">
        <clix:description>
          If set to a true value, JSON null will be read as the
          keyword :NULL, instead of NIL.
          NIL is the default.
        </clix:description>
      </clix:special-variable>

      <clix:special-variable name="*parse-object-key-fn*">
        <clix:description>
          Function to call to convert a key string in a JSON object to
          a key in the CL hash produced. IDENTITY is the default.
        </clix:description>
      </clix:special-variable>

    </clix:subchapter>

	<p>
		To avoid <a href="https://bishopfox.com/blog/json-interoperability-vulnerabilities">security issues</a>
        in Common Lisp code and/or downstream, on parsing JSON duplicate keys
		are rejected. If allowing that is a real use case, please send a patch
		providing a restart.
	</p>
  </clix:chapter>

  <clix:chapter name="encoding" title="Encoding JSON data">
    YASON provides two distinct modes to encode JSON data:
    applications can either create an in-memory representation of the
    data to be serialized, then have YASON convert it to JSON in one
    go, or they can use a set of macros to serialize the JSON data
    element-by-element, allowing fine-grained control over the layout
    of the generated data.

    <p>
      Optionally, the JSON that is produced can be indented.
      Indentation requires the use of a
      <clix:ref>JSON-OUTPUT-STREAM</clix:ref> as serialization target.
      With the stream serializer, such a stream is automatically used.
      If indentation is desired with the DOM serializer, such a stream
      can be obtained by calling the
      <clix:ref>MAKE-JSON-OUTPUT-STREAM</clix:ref> function with the
      target output string as argument.  Please be aware that indented
      output not requires more space, but is also slower and should
      not be enabled in performance critical applications.
    </p>

    <clix:subchapter name="dom-encoder" title="Encoding a JSON DOM">
      <p>
        In this mode, an in-memory structure is encoded in JSON
        format.  The structure must consist of objects that are
        serializable using the <clix:ref>ENCODE</clix:ref> function.
        YASON defines a number of encoders for standard data types
        (see <clix:ref>MAPPING</clix:ref>), but the application can
        define additional methods (e.g. for encoding CLOS objects).
      </p>
      For example:
      <pre>CL-USER&gt; (yason:encode
          (list (alexandria:plist-hash-table
                 '("foo" 1 "bar" (7 8 9))
                 :test #'equal)
                2 3 4
                '(5 6 7)
                t nil)
          *standard-output*)
[{"foo":1,"bar":[7,8,9]},2,3,4,[5,6,7],true,null]
(#&lt;HASH-TABLE :TEST EQUAL :COUNT 2 {59942D21}&gt; 2 3 4 (5 6 7) T NIL)</pre>

      <clix:subchapter name="dom-encoder-dict" title="DOM encoder dictionary">
        <clix:function name="encode" generic="true">
          <clix:lambda-list>object &amp;optional
          stream</clix:lambda-list>
          <clix:returns>object</clix:returns>
          <clix:description>
            Encode <clix:arg>object</clix:arg> in JSON format and
            write to <clix:arg>stream</clix:arg>.  May be specialized
            by applications to perform specific rendering. Stream
            defaults to *STANDARD-OUTPUT*.
          </clix:description>
        </clix:function>

	<clix:function name="encode-alist">
	  <clix:lambda-list>object &amp;optional (stream
	  *standard-output*)</clix:lambda-list>
	  <clix:returns>object</clix:returns>
	  <clix:description>
	    Encodes <clix:arg>object</clix:arg>, an alist, in JSON
	    format and write to <clix:arg>stream</clix:arg>.
	  </clix:description>
	</clix:function>

	<clix:function name="encode-plist">
	  <clix:lambda-list>object &amp;optional (stream
	  *standard-output*)</clix:lambda-list>
	  <clix:returns>object</clix:returns>
	  <clix:description>
	    Encodes <clix:arg>object</clix:arg>, a plist, in JSON
	    format and write to <clix:arg>stream</clix:arg>.
	  </clix:description>
	</clix:function>

        <clix:function name="make-json-output-stream">
          <clix:lambda-list>stream &amp;key (indent t)</clix:lambda-list>
          <clix:returns>stream</clix:returns>
          <clix:description>
            Creates a <clix:ref>json-output-stream</clix:ref> instance
            that wraps the supplied <clix:arg>stream</clix:arg> and
            optionally performs indentation of the generated JSON
            data.  The <clix:arg>indent</clix:arg> argument is
            described in <clix:ref>WITH-OUTPUT</clix:ref>.  Note that
            if the <clix:arg>indent</clix:arg> argument is NIL, the
            original stream is returned in order to avoid the
            performance penalty of the indentation algorithm.
          </clix:description>
        </clix:function>

      <clix:special-variable name="*list-encoder*">
        <clix:description>
          Function to call to translate a CL list into JSON data.
		  <clix:arg>'YASON:ENCODE-PLAIN-LIST-TO-ARRAY</clix:arg> is the default;
		  <clix:arg>'YASON:ENCODE-PLIST</clix:arg> and
		  <clix:arg>'YASON:ENCODE-ALIST</clix:arg> are available to produce
		  JSON objects.
		  <p>
			  This is useful to translate a deeply recursive structure in a single
			  <clix:arg>YASON:ENCODE</clix:arg> call.
          </p>
        </clix:description>
      </clix:special-variable>


      <clix:special-variable name="*symbol-encoder*">
        <clix:description>
          Function to call to translate a CL symbol into a JSON string.
		  The default is to error out, to provide backwards-compatible behaviour.
		  <p>
			  A useful function that can be bound to this variable is 
			  <clix:ref>YASON:ENCODE-SYMBOL-AS-LOWERCASE.</clix:ref>
		  </p>
        </clix:description>
      </clix:special-variable>


		<clix:special-variable name="*symbol-key-encoder*">
          <clix:description>
			  Defines the policy to encode symbols as keys (eg. in hash tables).
			  The default is to error out, to provide backwards-compatible behaviour.
			  <p>
				  A useful function that can be bound to this variable is 
				  <clix:ref>YASON:ENCODE-SYMBOL-AS-LOWERCASE.</clix:ref>
			  </p>
          </clix:description>
        </clix:special-variable>
      </clix:subchapter>
    </clix:subchapter>

    <clix:subchapter name="stream-encoder" title="Encoding JSON in streaming mode">
      <p>
        In this mode, the JSON structure is generated in a stream.
        The application makes explicit calls to the encoding library
        in order to generate the JSON structure.  It provides for more
        control over the generated output, and can be used to generate
        arbitary JSON without requiring that there exists a directly
        matching Lisp data structure.  The streaming API uses the
        <clix:ref>encode</clix:ref> function, so it is possible to
        intermix the two (see <clix:ref>app-encoders</clix:ref> for an
        example).
      </p>
      For example:
      <pre>CL-USER&gt; (yason:with-output (*standard-output*)
           (yason:with-array ()
             (dotimes (i 3)
               (yason:encode-array-element i))))
[0,1,2]
NIL
CL-USER&gt; (yason:with-output (*standard-output*)
           (yason:with-object ()
             (yason:encode-object-element "hello" "hu hu")
             (yason:with-object-element ("harr")
               (yason:with-array ()
                 (dotimes (i 3)
                   (yason:encode-array-element i))))))
{"hello":"hu hu","harr":[0,1,2]}
NIL</pre>

      <clix:subchapter name="stream-encoder-dict" title="Streaming encoder dictionary">
        <clix:function name="with-output" macro="true">
          <clix:lambda-list>(stream &amp;key indent) &amp;body body</clix:lambda-list>
          <clix:returns>result*</clix:returns>
          <clix:description>
            Set up a JSON streaming encoder context on
            <clix:arg>stream</clix:arg>, then evaluate
            <clix:arg>body</clix:arg>.  <clix:arg>indent</clix:arg>
            can be set to T to enable indentation with a default
            indentation width or to an integer specifying the desired
            indentation width.  By default, indentation is switched
            off.
          </clix:description>
        </clix:function>

        <clix:function name="with-output-to-string*" macro="true">
          <clix:lambda-list>(&amp;key indent stream-symbol) &amp;body body</clix:lambda-list>
          <clix:returns>result*</clix:returns>
          <clix:description>
			  Set up a JSON streaming encoder context on 
			  <clix:arg>stream-symbol</clix:arg> (by default 
			  a gensym), then evaluate
            <clix:arg>body</clix:arg>.  Return a string with the
            generated JSON output.  See
            <clix:ref>WITH-OUTPUT</clix:ref> for the description of
            the <clix:arg>indent</clix:arg> keyword argument.
          </clix:description>
        </clix:function>

        <clix:condition name="no-json-output-context">
          <clix:description>
            This condition is signalled when one of the stream
            encoding functions is used outside the dynamic context of
            a <clix:ref>WITH-OUTPUT</clix:ref> or
            <clix:ref>WITH-OUTPUT-TO-STRING*</clix:ref> body.
          </clix:description>
        </clix:condition>

        <clix:function name="with-array" macro="true">
          <clix:lambda-list>() &amp;body body</clix:lambda-list>
          <clix:returns>result*</clix:returns>
          <clix:description>
            Open a JSON array, then run <clix:arg>body</clix:arg>.
            Inside the body, <clix:ref>ENCODE-ARRAY-ELEMENT</clix:ref>
            must be called to encode elements to the opened array.
            Must be called within an existing JSON encoder context
            (see <clix:ref>WITH-OUTPUT</clix:ref> and
            <clix:ref>WITH-OUTPUT-TO-STRING*</clix:ref>).
          </clix:description>
        </clix:function>

        <clix:function name="encode-array-element">
          <clix:lambda-list>object</clix:lambda-list>
          <clix:returns>object</clix:returns>
          <clix:description>
            Encode <clix:arg>object</clix:arg> as next array element to
            the last JSON array opened
            with <clix:ref>WITH-ARRAY</clix:ref> in the dynamic
            context.  <clix:arg>object</clix:arg> is encoded using the
            <clix:ref>ENCODE</clix:ref> generic function, so it must be of
            a type for which an <clix:ref>ENCODE</clix:ref> method is
            defined.
          </clix:description>
        </clix:function>

	<clix:function name="encode-array-elements">
	  <clix:lambda-list>&amp;rest objects</clix:lambda-list>
	  <clix:returns>result*</clix:returns>
	  <clix:description>
	    Encode <clix:arg>objects</clix:arg>, a series of JSON
	    encodable objects, as the next array elements in a JSON
	    array opened with
	    <clix:ref>WITH-ARRAY</clix:ref>. ENCODE-ARRAY-ELEMENTS
	    uses <clix:ref>ENCODE-ARRAY-ELEMENT</clix:ref>, which must
	    be applicable to each object in the list
	    (i.e. <clix:ref>ENCODE</clix:ref> must be defined for each
	    object type). Additionally, this must be called within a
	    valid stream context.
	  </clix:description>
	</clix:function>

        <clix:function name="with-object" macro="true">
          <clix:lambda-list>() &amp;body body</clix:lambda-list>
          <clix:returns>result*</clix:returns>
          <clix:description>
            Open a JSON object, then run <clix:arg>body</clix:arg>.
            Inside the body,
            <clix:ref>ENCODE-OBJECT-ELEMENT</clix:ref> or
            <clix:ref>WITH-OBJECT-ELEMENT</clix:ref> must be called to
            encode elements to the object.  Must be called within an
            existing JSON encoder
            <clix:ref>WITH-OUTPUT</clix:ref> and
            <clix:ref>WITH-OUTPUT-TO-STRING*</clix:ref>.
          </clix:description>
        </clix:function>

        <clix:function name="with-object-element" macro="true">
          <clix:lambda-list>(key) &amp;body body</clix:lambda-list>
          <clix:returns>result*</clix:returns>
          <clix:description>
            Open a new encoding context to encode a JSON object
            element.  <clix:arg>key</clix:arg> is the key of the
            element.  The value will be whatever
            <clix:arg>body</clix:arg> serializes to the current JSON
            output context using one of the stream encoding functions.
            This can be used to stream out nested object structures.
          </clix:description>
        </clix:function>

        <clix:function name="encode-object-element">
          <clix:lambda-list>key value</clix:lambda-list>
          <clix:returns>value</clix:returns>
          <clix:description>
            Encode <clix:arg>key</clix:arg> and
            <clix:arg>value</clix:arg> as object element to the last
            JSON object opened with <clix:ref>WITH-OBJECT</clix:ref>
            in the dynamic context.  <clix:arg>key</clix:arg> and
            <clix:arg>value</clix:arg> are encoded using the
            <clix:ref>ENCODE</clix:ref> generic function, so they both
            must be of a type for which an <clix:ref>ENCODE</clix:ref>
            method is defined.
          </clix:description>
        </clix:function>

	<clix:function name="encode-object-elements">
	  <clix:lambda-list>&amp;rest elements</clix:lambda-list>
	  <clix:returns>result*</clix:returns>
	  <clix:description>
	    Encodes the parameters into JSON in the last object opened
	    with <clix:ref>WITH-OBJECT</clix:ref> using
	    <clix:ref>ENCODE-OBJECT-ELEMENT</clix:ref>. The parameters
	    should consist of alternating key/value pairs, and this
	    must be called within a valid stream context.
	  </clix:description>
	</clix:function>

	<clix:function name="encode-object-slots">
		<clix:lambda-list>object slots</clix:lambda-list>
		<clix:returns>result*</clix:returns>
		<clix:description>
			Encodes each slot in SLOTS for OBJECT in the last object
			opened with <clix:ref>WITH-OBJECT</clix:ref> using
			<clix:ref>ENCODE-OBJECT-ELEMENT</clix:ref>. The key is the
			slot name, and the value is the slot value for the slot on
			OBJECT. It is equivalent to
			<pre>(loop for slot in slots
    do (encode-object-element (string slot)
                              (slot-value object slot)))
			</pre>
		</clix:description>
	</clix:function>

	<clix:function name="encode-slots">
	  <clix:lambda-list>object</clix:lambda-list>
	  <clix:returns>result*</clix:returns>
	  <clix:description>
            Generic function to encode object slots. There is no default
            implementation.
            It should be called in an object encoding context. It uses
            PROGN combinatation with MOST-SPECIFIC-LAST order, so that
            base class slots are encoded before derived class slots.
	  </clix:description>
	</clix:function>

	<clix:function name="encode-object">
	  <clix:lambda-list>object</clix:lambda-list>
	  <clix:returns>result*</clix:returns>
	  <clix:description>
            Generic function to encode an object. The default implementation
            opens a new object encoding context and calls
            <clix:ref>ENCODE-SLOTS</clix:ref> on the argument.
	  </clix:description>
	</clix:function>

        <clix:class name="json-output-stream">
          <clix:description>
            Instances of this class are used to wrap an output stream
            that is used as a serialization target in the stream
            encoder and optionally in the DOM encoder if indentation
            is desired.  The class name is not exported, use
            <clix:ref>make-json-output-stream</clix:ref> to create a
            wrapper stream if required.
          </clix:description>
        </clix:class>
      </clix:subchapter>
    </clix:subchapter>

    <clix:subchapter name="app-encoders" title="Application specific encoders">

      Suppose your application uses structs to represent its data and
      you want to encode these structs using JSON in order to send
      them to a client application.  Suppose further that your structs
      also include internal information that you do not want to send.
      Here is some code that illustrates how one could implement a
      serialization function:

      <pre>CL-USER&gt; (defstruct user name age password)
USER
CL-USER&gt; (defmethod yason:encode ((user user) &amp;optional (stream *standard-output*))
           (yason:with-output (stream)
             (yason:with-object ()
               (yason:encode-object-element "name" (user-name user))
               (yason:encode-object-element "age" (user-age user)))))
#&lt;STANDARD-METHOD YASON:ENCODE (USER) {5B40A591}&gt;
CL-USER&gt; (yason:encode (list (make-user :name "horst" :age 27 :password "puppy")
                            (make-user :name "uschi" :age 28 :password "kitten")))
[{"name":"horst","age":27},{"name":"uschi","age":28}]
(#S(USER :NAME "horst" :AGE 27 :PASSWORD "puppy")
 #S(USER :NAME "uschi" :AGE 28 :PASSWORD "kitten"))</pre>

      As you can see, the streaming API and the DOM encoder can be
      used together.  <clix:ref>ENCODE</clix:ref> invokes itself
      recursively, so any application defined method will be called
      while encoding in-memory objects as appropriate.

      <p>For an example of the interplay between
      <clix:ref>ENCODE-OBJECT</clix:ref> and
      <clix:ref>ENCODE-SLOTS</clix:ref>, suppose you have the following
      CLOS class heirarchy:

      <pre>(defclass shape ()
  ((color :reader color)))

(defclass square (shape)
  ((side-length :reader side-length)))

(defclass circle (shape)
  ((radius :reader radius)))</pre>

      In order to implement encoding of circles and squares without
      duplicating code you can specialize
      <clix:ref>ENCODE-SLOTS</clix:ref> for all three classes

      <pre>(defmethod yason:encode-slots progn ((shape shape))
  (yason:encode-object-element "color" (color shape)))

(defmethod yason:encode-slots progn ((square square))
  (yason:encode-object-element "side-length" (side-length square)))

(defmethod yason:encode-slots progn ((circle circle))
  (yason:encode-object-element "radius" (radius circle)))</pre>

      and then use <clix:ref>ENCODE-OBJECT</clix:ref>:

      <pre>CL-USER&gt; (yason:with-output-to-string* ()
           (yason:encode-object (make-instance 'square :color "red" :side-length 3)))
"{\"color\":\"red\",\"side-length\":3}"
CL-USER&gt; (yason:with-output-to-string* ()
           (yason:encode-object (make-instance 'circle :color "blue" :side-length 5)))
"{\"color\":\"blue\",\"radius\":5}"</pre>
      </p>
	  <p>Alternatively, you can use the shortcut <clix:ref>ENCODE-OBJECT-SLOTS</clix:ref>
	  if you want the keys to be the slot names. For example:
	  <pre>(defclass person ()
  ((name :reader name :initarg :name)
   (address :reader address :initarg :address)
   (phone-number :reader phone-number :initarg :phone)
   (favorite-color :reader favorite-color :initarg :color)))

(defmethod yason:encode-slots progn ((person person))
  (yason:encode-object-slots person '(name address phone-number favorite-color)))</pre>
  and then:

  <pre>CL-USER&gt; (yason:with-output-to-string* ()
       (yason:encode-object (make-instance 'person :name "John Doe"
                                                   :address "123 Main St."
                                                   :phone "(123)-456-7890"
                                                   :color "blue")))
"{\"NAME\":\"John Doe\",\"ADDRESS\":\"123 Main St.\",\"PHONE-NUMBER\":\"(123)-456-7890\",
\"FAVORITE-COLOR\":\"blue\"}"</pre>
	  </p>
    </clix:subchapter>
  </clix:chapter>

  <clix:chapter name="index" title="Symbol index">
    <clix:index/>
  </clix:chapter>

  <clix:chapter name="license" title="License">
    <pre class="none">Copyright (c) 2008-2014 Hans Hübner and contributors
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

  - Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.

  - Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in
    the documentation and/or other materials provided with the
    distribution.

  - Neither the name BKNR nor the names of its contributors may be
    used to endorse or promote products derived from this software
    without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
</pre>
  </clix:chapter>

  <clix:chapter name="ack" title="Acknowledgements">
    Thanks go to Edi Weitz for being a great inspiration.  This
    documentation as been generated with a hacked-up version of his <a
    href="http://weitz.de/documentation-template/">DOCUMENTATION-TEMPLATE</a>
    software.  Thanks to David Lichteblau for coining YASON's name.
  </clix:chapter>

</clix:documentation>