code: def bind(proc=nil, &block)
        return self if failure?
        return concat(proc) if proc.is_a? Either
  
        begin
          Either(call(proc, block))
        rescue StandardError => error
          Failure(error)
        end
      end
docs: Allows privileged access to the +Either+'s inner value from within a block.
   This block should return a +Success+ or +Failure+ itself. It will be coerced into #Either
   @return [Success, Failure]