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<document>
  <properties>
    <title>Commons JEXL Syntax</title>
  </properties>

  <body>
    <section name="Overview">
      <p>
        This reference is split up into the following sections:
        <ol>
          <li><a href="#Language Elements">Language Elements</a></li>
          <li><a href="#Literals">Literals</a></li>
          <li><a href="#Functions">Functions</a></li>
          <li><a href="#Operators">Operators</a></li>
          <li><a href="#Conditional">Conditional Statements</a></li>
        </ol>
      </p>
      <p>
        For more technical information about the JEXL Grammar, you can find the
        <a href="https://javacc.dev.java.net/">JavaCC</a> grammar for JEXL
        here: <a href="http://svn.apache.org/viewcvs.cgi/jakarta/commons/proper/jexl/trunk/src/java/org/apache/commons/jexl/parser/Parser.jj?view=markup">Parser.jj</a>
      </p>
    </section>
    <section name="Language Elements">
      <table>
        <tr><th width="15%">Item</th><th>Description</th></tr>
        <tr>
          <td>Comments</td>
          <td>
            Specified using <code>##</code> and extend to the end of line, e.g.
            <source>## This is a comment</source>
          </td>
        </tr>
        <tr>
          <td>Identifiers / variables</td>
          <td>
            Must start with <code>a-z</code>, <code>A-Z</code>, <code>_</code> or <code>$</code>.
            Can then be followed by <code>0-9</code>, <code>a-z</code>, <code>A-Z</code>, <code>_</code> or <code>$</code>.
            e.g.
            <ul>
              <li>Valid: <code>var1</code>,<code>_a99</code>,<code>$1</code></li>
              <li>Invalid: <code>9v</code>,<code>!a99</code>,<code>1$</code></li>
            </ul>
            <p>
              JEXL also supports <code>ant-style</code> variables, e.g. <source>my.dotted.var</source>
              is a valid variable name.
            </p>
            <p>
              <strong>NOTE:</strong> JEXL does not support variables with hyphens in them, e.g.
              <source>commons-logging</source> is not a valid variable, but instead is treated as a
              subtraction of the variable <code>logging</code> from the variable <code>commons</code>
            </p>
          </td>
        </tr>
        <tr>
          <td>Scripts</td>
          <td>
            A script in Jexl is made up of zero or more statements. Scripts can be read from a String, File or URL.
          </td>
        </tr>
        <tr>
          <td>Statements</td>
          <td>
            A statement can be the empty statement, the semicolon (<code>;</code>) ,  block, assignment or an expression.
            Statements are optionally terminated with a semicolon.
          </td>
        </tr>
        <tr>
          <td>Block</td>
          <td>
            A block is simply multiple statements inside curly braces (<code>{, }</code>).
          </td>
        </tr>
      </table>
    </section>
    <section name="Literals">
      <table>
        <tr><th width="15%">Item</th><th>Description</th></tr>
        <tr>
          <td>Integer Literals</td>
          <td>1 or more digits from <code>0</code> to <code>9</code></td>
        </tr>
        <tr>
          <td>Floating point Literals</td>
          <td>
            1 or more digits from <code>0</code> to <code>9</code>, followed
            by a decimal point and then one or more digits from
            <code>0</code> to <code>9</code>. 
          </td>
        </tr>
        <tr>
          <td>String literals</td>
          <td>
            Can start and end with either <code>'</code> or <code>"</code>, e.g.
            <source>"Hello world"</source> and
            <source>'Hello world'</source> are equivalent.
          </td>
        </tr>
        <tr>
          <td>Boolean literals</td>
          <td>
            The literals <code>true</code> and <code>false</code> can be used, e.g.
            <source>val1 == true</source>
          </td>
        </tr>
        <tr>
          <td>Null literal</td>
          <td>
            The null value is represented as in java using the literal <code>null</code>, e.g.
            <source>val1 == null</source>
          </td>
        </tr>
      </table>
    </section>
    <section name="Functions">
      <table>
        <tr><th width="15%">Function</th><th>Description</th></tr>
        <tr>
          <td>empty</td>
          <td>
            Returns true if the expression following is either:
            <ol>
              <li><code>null</code></li>
              <li>An empty string</li>
              <li>An array of length zero</li>
              <li>A collection of size zero</li>
              <li>An empty map</li>
            </ol>
            <source>empty(var1)</source>
          </td>
        </tr>
        <tr>
          <td>size</td>
          <td>
            Returns the information about the expression:
            <ol>
              <li>Length of an array</li>
              <li>Size of a List</li>
              <li>Size of a Map</li>
              <li>Size of a Set</li>
              <li>Length of a string</li>
            </ol>
            <source>size("Hello")</source> returns 5.
          </td>
        </tr>
      </table>
    </section>
    <section name="Operators">
      <table>
        <tr><th width="15%">Operator</th><th>Description</th></tr>
        <tr>
          <td>Boolean <code>and</code></td>
          <td>
            The usual <code>&amp;&amp;</code> operator can be used as well as the word <code>and</code>, e.g.
            <source>cond1 and cond2</source> and
            <source>cond1 &amp;&amp; cond2</source> are equivalent
          </td>
        </tr>
        <tr>
          <td>Boolean <code>or</code></td>
          <td>
            The usual <code>||</code> operator can be used as well as the word <code>or</code>, e.g.
            <source>cond1 or cond2</source> and
            <source>cond1 || cond2</source> are equivalent
          </td>
        </tr>
        <tr>
          <td>Boolean <code>not</code></td>
          <td>
            The usual <code>!</code> operator can be used as well as the word <code>not</code>, e.g.
            <source>!cond1</source> and
            <source>not cond1</source> are equivalent
          </td>
        </tr>
        <tr>
          <td>Bitwise <code>and</code></td>
          <td>
            The usual <code>&amp;</code> operator is used, e.g. 
            <source>33 &amp; 4</source>, 0010 0001 &amp; 0000 0100 = 0.
          </td>
        </tr>
        <tr>
          <td>Bitwise <code>or</code></td>
          <td>
            The usual <code>|</code> operator is used, e.g.
            <source>33 | 4</source>, 0010 0001 | 0000 0100 = 0010 0101 = 37.
          </td>
        </tr>
        <tr>
          <td>Bitwise <code>xor</code></td>
          <td>
            The usual <code>^</code> operator is used, e.g.
            <source>33 ^ 4</source>, 0010 0001 ^ 0000 0100 = 0010 0100 = 37.
          </td>
        </tr>
        <tr>
          <td>Bitwise <code>complement</code></td>
          <td>
            The usual <code>~</code> operator is used, e.g.
            <source>~33</source>, ~0010 0001 = 1101 1110 = -34.
          </td>
        </tr>
        <tr>
          <td>Equality</td>
          <td>
            The usual <code>==</code> operator can be used as well as the abbreviation <code>eq</code>.
            For example 
            <source>val1 == val2</source> and
            <source>val1 eq val2</source> are equivalent.
            <ol>
              <li>
                <code>null</code> is only ever equal to null, that is if you compare null
                to any non-null value, the result is false.
              </li>
              <li>Equality uses the java <code>equals</code> method</li>
            </ol>
          </td>
        </tr>
        <tr>
          <td>Inequality</td>
          <td>
            The usual <code>!=</code> operator can be used as well as the abbreviation <code>ne</code>.
            For example
            <source>val1 != val2</source> and
            <source>val1 ne val2</source> are equivalent.
          </td>
        </tr>
        <tr>
          <td>Less Than</td>
          <td>
            The usual <code>&lt;</code> operator can be used as well as the abbreviation <code>lt</code>.
            For example
            <source>val1 &lt; val2</source> and
            <source>val1 lt val2</source> are equivalent.
          </td>
        </tr>
        <tr>
          <td>Less Than Or Equal To</td>
          <td>
            The usual <code>&lt;=</code> operator can be used as well as the abbreviation <code>le</code>.
            For example
            <source>val1 &lt;= val2</source> and
            <source>val1 le val2</source> are equivalent.
          </td>
        </tr>
        <tr>
          <td>Greater Than</td>
          <td>
            The usual <code>&gt;</code> operator can be used as well as the abbreviation <code>gt</code>.
            For example
            <source>val1 &gt; val2</source> and
            <source>val1 gt val2</source> are equivalent.
          </td>
        </tr>
        <tr>
          <td>Greater Than Or Equal To</td>
          <td>
            The usual <code>&gt;=</code> operator can be used as well as the abbreviation <code>ge</code>.
            For example
            <source>val1 &gt;= val2</source> and
            <source>val1 ge val2</source> are equivalent.
          </td>
        </tr>
        <tr>
          <td>Addition</td>
          <td>
            The usual <code>+</code> operator is used.
            For example
            <source>val1 + val2</source>
          </td>
        </tr>
        <tr>
          <td>Subtraction</td>
          <td>
            The usual <code>-</code> operator is used.
            For example
            <source>val1 - val2</source>
          </td>
        </tr>
        <tr>
          <td>Multiplication</td>
          <td>
            The usual <code>*</code> operator is used.
            For example
            <source>val1 * val2</source>
          </td>
        </tr>
        <tr>
          <td>Division</td>
          <td>
            The usual <code>/</code> operator is used.
            For example
            <source>val1 / val2</source>
          </td>
        </tr>
        <tr>
          <td>Integer Division</td>
          <td>
            The <code>div</code> operator is used.
            For example
            <source>4 div 3</source> gives 1.
          </td>
        </tr>
        <tr>
          <td>Modulus (or remainder)</td>
          <td>
            The <code>%</code> operator is used. An alternative is the <code>mod</code>
            operator.
            For example
            <source>5 mod 2</source> gives 1 and is equivalent to <source>5 % 2</source>
          </td>
        </tr>
        <tr>
          <td>Negation</td>
          <td>
            The unary <code>-</code> operator is used.
            For example
            <source>-12</source>
          </td>
        </tr>
        <tr>
          <td>Array access</td>
          <td>
            Array elements may be accessed using either square brackets or a dotted numeral, e.g.
            <source>arr1[0]</source> and <source>arr1.0</source> are equivalent
          </td>
        </tr>
      </table>
    </section>
    <section name="Conditional">
      <table>
        <tr><th width="15%">Operator</th><th>Description</th></tr>
        <tr>
          <td>if</td>
          <td>
            Classic, if/else statement, e.g.
            <code>if ((x * 2) == 5) {y = 1;} else {y = 2;}</code>
          </td>
        </tr>
        <tr>
          <td>foreach</td>
          <td>
            Loop through items of an Array, Collection, Map, Iterator or Enumeration, e.g.
            <code>foreach (item in list) { x = x + item; }</code>
            Where <code>item</code> and <code>list</code> are variables.
          </td>
        </tr>
        <tr>
          <td>while</td>
          <td>
            Loop until a condition is satisfied, e.g.
            <code>while (x lt 10) { x = x + 2; }</code>
          </td>
        </tr>
      </table>
    </section>

  </body>
</document>
    