public function addFunction(Compiler $compiler, FunctionDefinition $func, $statement = null)
{
$compiler->addFunction($func, $statement);
$funcName = strtolower($func->getInternalName());
if (isset($this->_functionDefinitions[$funcName])) {
throw new CompilerException("Function '" . $func->getName() . "' was defined more than one time (in the same file)", $statement);
}
$this->_functionDefinitions[$funcName] = $func;
}