(PECL runkit >= 0.7.0)
runkit_function_copy — Copy a function to a new function name
$funcname
   , string $targetname
   )
funcnameName of existing function
targetnameName of new function to copy definition to
   Returns TRUE on success or FALSE on failure.
  
Example #1 A runkit_function_copy() example
<?php
function original() {
  echo "In a function\n";
}
runkit_function_copy('original','duplicate');
original();
duplicate();
?>
The above example will output:
In a function In a function