class Haml::Exec::Generic

def process_result

so they can run their respective programs.
This is meant to be overridden by subclasses

to appropriate IO streams.
In particular, sets `@options[:input]` and `@options[:output]`
Processes the options set by the command-line arguments. 
def process_result
  input, output = @options[:input], @options[:output]
  args = @args.dup
  input ||=
    begin
      filename = args.shift
      @options[:filename] = filename
      open_file(filename) || $stdin
    end
  output ||= open_file(args.shift, 'w') || $stdout
  @options[:input], @options[:output] = input, output
end