original_string: public static function forSum(callable $num): self {
          return new self(
                  function() { return 0; },
                  function(&$result, $element) use($num) { $result+= $num($element); }
          );
      }
code: public static function forSum(callable $num): self {
          return new self(
                  function() { return 0; },
                  function(&$result, $element) use($num) { $result+= $num($element); }
          );
      }
code_tokens: public static function forSum ( callable $ num ) : self { return new self ( function ( ) { return 0 ; } , function ( & $ result , $ element ) use ( $ num ) { $ result += $ num ( $ element ) ; } ) ; }
docstring: returns a collector to sum up elements
  
  @api
  @param   callable  $num  callable which retrieves a number from a given element
  @return  \stubbles\sequence\Collector
docstring_tokens: returns a collector to sum up elements