15.4.908  src/lib/src/io-with.pkg

## io-with.pkg

# Compiled by:
#     src/lib/std/standard.lib



###             "My method is to take the utmost trouble
###              to find the right thing to say.
###
###             "And then say it with the utmost levity."
###
###                         -- George Bernard Shaw



stipulate
    package fil =  file__premicrothread;        # file__premicrothread          is from   src/lib/std/src/posix/file--premicrothread.pkg
herein

    package   io_with
    : (weak)  Io_With           # Io_With       is from   src/lib/src/io-with.api
    {
        Input_Stream  =  fil::Input_Stream;
        Output_Stream =  fil::Output_Stream;

        fun swap_instream (s, s')
            =
            fil::get_instream  s
            then
                fil::set_instream (s, s');

        fun with_input_file (s, f) x
            =
            result
            where
                old_strm
                    =
                    swap_instream
                      ( fil::stdin,
                        fil::get_instream (fil::open_for_read s)
                      );

                fun clean_up ()
                    =
                    fil::pur::close_input
                        #
                        (swap_instream (fil::stdin, old_strm));

                result
                    =
                    (f x)
                    except
                        x = {   clean_up ();
                                raise exception x;
                            };

                clean_up();
            end;

        #
        fun with_instream (stream, f) x
            =
            {   old_strm =   swap_instream (fil::stdin, fil::get_instream stream);
                #
                fun clean_up ()
                    =
                    fil::set_instream (stream, swap_instream (fil::stdin, old_strm));

                result
                    =
                    (f x)
                    except
                        ex =  {   clean_up ();
                                  raise exception ex;
                              };

                clean_up();

                result;
            };

        fun swap_outstrm (s, s')
            =
            fil::get_outstream  s
            then
                fil::set_outstream (s, s');


        fun with_output_file (s, f) x
            =
            {   old_strm
                    =
                    swap_outstrm
                      ( fil::stdout,
                        fil::get_outstream (fil::open_for_write s)
                      );

                fun clean_up ()
                    =
                    fil::pur::close_output (swap_outstrm (fil::stdout, old_strm));

                result =    (f x)
                            except
                                x = {   clean_up ();
                                        raise exception x;
                                    };

                clean_up();

                result;
            };

        fun with_outstream (stream, f) x
            =
            {   old_strm
                    =
                    swap_outstrm
                      ( fil::stdout,
                        fil::get_outstream stream
                      );

                fun clean_up ()
                    =
                    fil::set_outstream (stream, swap_outstrm (fil::stdout, old_strm));

                result =    f x
                            except
                                x = {   clean_up ();
                                        raise exception x;
                                    };

                clean_up ();

                result;
            };

    };                          # package io_with 
end;