Temporary Files And Directories in Prolog

Our program demonstrates how to work with temporary files and directories in Prolog. Here’s the full source code:

:- use_module(library(system)).
:- use_module(library(process)).

main :-
    % Create a temporary file
    tmp_file_stream(text, TempFile, Stream),
    write(Stream, [1, 2, 3, 4]),
    close(Stream),
    format('Temp file name: ~w~n', [TempFile]),

    % Clean up the file after we're done
    catch(delete_file(TempFile), _, true),

    % Create a temporary directory
    tmp_directory(TempDir),
    format('Temp dir name: ~w~n', [TempDir]),

    % Create a file in the temporary directory
    atomic_list_concat([TempDir, '/file1'], FileName),
    open(FileName, write, FileStream),
    write(FileStream, [1, 2]),
    close(FileStream),

    % Clean up the directory after we're done
    catch(delete_directory_and_contents(TempDir), _, true).

% Helper predicate to delete a directory and its contents
delete_directory_and_contents(Dir) :-
    directory_files(Dir, Files),
    delete_files(Files, Dir),
    delete_directory(Dir).

delete_files([], _).
delete_files([File|Rest], Dir) :-
    File \= '.',
    File \= '..',
    atomic_list_concat([Dir, '/', File], FullPath),
    (exists_directory(FullPath) ->
        delete_directory_and_contents(FullPath)
    ;   delete_file(FullPath)
    ),
    delete_files(Rest, Dir).

In Prolog, we use the system and process libraries to handle file and directory operations. Let’s break down the code:

1. We create a temporary file using tmp_file_stream/3. This predicate creates a file with a unique name and opens a stream to it.

2. We write some data to the file using write/2.

3. We display the name of the temporary file using format/2.

4. We use catch/3 to attempt to delete the file after we’re done with it.

5. To create a temporary directory, we use tmp_directory/1. This predicate creates a directory with a unique name.

6. We display the name of the temporary directory.

7. We create a file inside the temporary directory by constructing its path using atomic_list_concat/2.

8. We write some data to this file.

9. Finally, we clean up by deleting the temporary directory and its contents using our custom delete_directory_and_contents/1 predicate.

The delete_directory_and_contents/1 predicate recursively deletes a directory and all its contents. It first lists all files in the directory, then deletes each file or subdirectory, and finally deletes the directory itself.

To run the program, you can save it as temp_files_and_dirs.pl and use the Prolog interpreter:

$ swipl -s temp_files_and_dirs.pl -g main -t halt
Temp file name: /tmp/swipl_tmp_file_2135_1
Temp dir name: /tmp/swipl_tmp_dir_2135_0

This program demonstrates how to create and manage temporary files and directories in Prolog, which can be useful for various tasks that require temporary storage during program execution.