public function next()
    {
        $operation   = $this->operation;
        $this->value = $operation($this->value);
        $this->elementsGenerated++;
    }
public function next()
    {
        $operation   = $this->operation;
        $this->value = $operation($this->value);
        $this->elementsGenerated++;
    }
public function next ( ) { $ operation = $ this -> operation ; $ this -> value = $ operation ( $ this -> value ) ; $ this -> elementsGenerated ++ ; }
generates next value
generates next value