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  <refentry id="function.create-function">
   <refnamediv>
    <refname>create_function</refname>
    <refpurpose>Create an anonymous (lambda-style) function</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>string</type><methodname>create_function</methodname>
      <methodparam><type>string</type><parameter>args</parameter></methodparam>
      <methodparam><type>string</type><parameter>code</parameter></methodparam>
     </methodsynopsis>
    <para>
     Creates an anonymous function from the parameters passed, and
     returns a unique name for it. Usually the
     <parameter>args</parameter> will be passed as a single quote
     delimited string, and this is also recommended for the
     <parameter>code</parameter>. The reason for using single quoted
     strings, is to protect
     the variable names from parsing, otherwise, if you use double
     quotes there will be a need to escape the variable names, e.g. 
     <literal>\$avar</literal>.
    </para>
    <para>
     You can use this function, to (for example) create a function
     from information gathered at run time:
    </para>
    <para>
     <example>
      <title>
       Creating an anonymous function with <function>create_function</function>
      </title>
      <programlisting role="php">
<![CDATA[
<?php
$newfunc = create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);');
echo "New anonymous function: $newfunc\n";
echo $newfunc(2, M_E) . "\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>
]]>
      </programlisting>
     </example>
    </para>
    <para>
     Or, perhaps to have general handler function that can apply a set
     of operations to a list of parameters:
    </para>
    <para>
     <example>
      <title>
       Making a general processing function with
       <function>create_function</function>
      </title>
      <programlisting role="php">
<![CDATA[
<?php
function process($var1, $var2, $farr) 
{
    foreach ($farr as $f) {
        echo $f($var1, $var2) . "\n";
    }
}

// create a bunch of math functions
$f1 = 'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}';
$f2 = "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);";
$f3 = 'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }';
$farr = array(
    create_function('$x,$y', 'return "some trig: ".(sin($x) + $x*cos($y));'),
    create_function('$x,$y', 'return "a hypotenuse: ".sqrt($x*$x + $y*$y);'),
    create_function('$a,$b', $f1),
    create_function('$a,$b', $f2),
    create_function('$a,$b', $f3)
    );

echo "\nUsing the first array of anonymous functions\n";
echo "parameters: 2.3445, M_PI\n";
process(2.3445, M_PI, $farr);

// now make a bunch of string processing functions
$garr = array(
    create_function('$b,$a', 'if (strncmp($a, $b, 3) == 0) return "** \"$a\" '.
    'and \"$b\"\n** Look the same to me! (looking at the first 3 chars)";'),
    create_function('$a,$b', '; return "CRCs: " . crc32($a) . " , ".crc32(b);'),
    create_function('$a,$b', '; return "similar(a,b) = " . similar_text($a, $b, &$p) . "($p%)";')
    );
echo "\nUsing the second array of anonymous functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>
]]>
      </programlisting>
      <para>
       and when you run the code above, the output will be:
      </para>
      <screen>
<![CDATA[
Using the first array of anonymous functions
parameters: 2.3445, M_PI
some trig: -1.6291725057799
a hypotenuse: 3.9199852871011
b*a^2 = 4.8103313314525
min(b^2+a, a^2,b) = 8.6382729035898
ln(a/b) = 0.27122299212594

Using the second array of anonymous functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: -725381282 , 1908338681
similar(a,b) = 11(45.833333333333%)
]]>
      </screen>
     </example>
    </para>
    <para>
     But perhaps the most common use for of lambda-style (anonymous) functions
     is to create callback functions, for example when using
     <function>array_walk</function> or <function>usort</function>
    </para>
    <para>
     <example>
      <title>Using anonymous functions as callback functions</title>
      <programlisting role="php">
<![CDATA[
<?php
$av = array("the ", "a ", "that ", "this ");
array_walk($av, create_function('&$v,$k', '$v = $v . "mango";'));
print_r($av); 
?>
]]>
      </programlisting>
      <para>
       outputs:
      </para>
      <screen>
<![CDATA[
Array
(
  [0] => the mango
  [1] => a mango
  [2] => that mango
  [3] => this mango
)
]]>
      </screen>
      <para>
       an array of strings ordered from shorter to longer
      </para>
      <programlisting role="php">
<![CDATA[
<?php

$sv = array("small", "larger", "a big string", "it is a string thing");
print_r($sv);

?>
]]>
      </programlisting>
      <para>
       outputs:
      </para>
      <screen>
<![CDATA[
Array
(
  [0] => small
  [1] => larger
  [2] => a big string
  [3] => it is a string thing
)
]]>
      </screen>
      <para>
       sort it from longer to shorter
      </para>
      <programlisting role="php">
<![CDATA[
<?php

usort($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);

?>
]]>
      </programlisting>
      <para>
       outputs:
      </para>
      <screen>
<![CDATA[
Array
(
  [0] => it is a string thing
  [1] => a big string
  [2] => larger
  [3] => small
)
]]>
      </screen>
     </example>
    </para>
   </refsect1>
  </refentry>

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