5.3.1.5 The save-task-list function

The code for save-task-list is shown below. Because this function does not use any DUIM code, it is described only briefly.

define function save-task-list
    (task-list :: <task-list>, #key filename)
 => (saved? :: <boolean>)
  let filename = filename | task-list-filename(task-list);
  with-open-file (stream = filename, direction: #"output")
    for (task in task-list.task-list-tasks)
      format(stream, "%s\n%s\n",
             task.task-name, as(<string>, task.task-priority))
    end
  end;
  task-list.task-list-modified? := #f;
  task-list.task-list-filename := filename;
  #t
end function save-task-list;

Add this code to task-list.dylan.

The function save-task-list takes an instance of <task-list> as an argument, and optionally a filename. It then attempts to save the instance of <task-list> to the file specified by filename. It returns a boolean value that indicates whether the file was successfully saved or not. If filename is not passed as an argument to save-task-list (in the case where the user has chosen File > Save or clicked the Save button when working with a task list file that has previously been saved), then the task-list-filename slot of the <task-list> is used instead.

Like load-task-list, this function uses the Streams library to save information to a file. For full information about this library, please refer to the I/O and Networks Library Reference. It also uses the format function from the Format library, which is described in the same reference.

The file is opened for saving using the with-open-file macro (just like load-task-list, but in the opposite direction), A for loop is used to save each element in each task to the file. The format function then writes each element to the file, separated by a newline character. Note how the as method is used to convert the task-priority symbol to a string when saving each priority value: this is the reverse situation to load-task-list, where a method for as was used to convert the string to a symbol.

Once every element in the file has been saved, the task-list-modified slot of the <task-list> is reset to #f, and the task-list-filename slot of the <task-list> is set to the filename used by save-task-list. This last step is necessary to allow for the case where the user has chosen the File > Save As command to save the file under a different name.

Finally, save-task-list returns #t to indicate that the file has been successfully saved.

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Building Applications Using DUIM - 26 May 1999