Directories in Prolog

% Our first program will demonstrate working with directories in Prolog.
% We'll use the SWI-Prolog's built-in predicates for file system operations.

% Helper predicate to handle errors
check_error(Error) :-
    (   Error == true
    ->  true
    ;   throw(Error)
    ).

% Main predicate
main :-
    % Create a new sub-directory in the current working directory
    make_directory('subdir'),

    % When creating temporary directories, it's good practice to clean them up afterwards
    catch(
        (   % Create files and subdirectories
            create_empty_file('subdir/file1'),
            make_directory_path('subdir/parent/child'),
            create_empty_file('subdir/parent/file2'),
            create_empty_file('subdir/parent/file3'),
            create_empty_file('subdir/parent/child/file4'),

            % List directory contents
            writeln('Listing subdir/parent'),
            directory_files('subdir/parent', Files),
            maplist(print_file_info('subdir/parent'), Files),

            % Change current working directory
            working_directory(_, 'subdir/parent/child'),

            % List contents of current directory
            writeln('Listing subdir/parent/child'),
            directory_files('.', ChildFiles),
            maplist(print_file_info('.'), ChildFiles),

            % Change back to the original directory
            working_directory(_, '../../..'),

            % Visit directory recursively
            writeln('Visiting subdir'),
            directory_walk('subdir', visit)
        ),
        Error,
        (check_error(Error), delete_directory_and_contents('subdir'))
    ),
    delete_directory_and_contents('subdir').

% Helper predicate to create an empty file
create_empty_file(Name) :-
    open(Name, write, Stream),
    close(Stream).

% Helper predicate to print file information
print_file_info(Dir, File) :-
    (File \= '.' , File \= '..' ->
        atomic_list_concat([Dir, '/', File], FullPath),
        (exists_directory(FullPath) ->
            format(' ~w true~n', [File])
        ;
            format(' ~w false~n', [File])
        )
    ; true).

% Predicate to visit files and directories recursively
visit(Path) :-
    (exists_directory(Path) ->
        format(' ~w true~n', [Path])
    ;
        format(' ~w false~n', [Path])
    ).

% Predicate to walk through a directory recursively
directory_walk(Dir, Predicate) :-
    directory_files(Dir, Files),
    maplist(process_file(Dir, Predicate), Files).

process_file(Dir, Predicate, File) :-
    (File \= '.' , File \= '..' ->
        atomic_list_concat([Dir, '/', File], FullPath),
        call(Predicate, FullPath),
        (exists_directory(FullPath) ->
            directory_walk(FullPath, Predicate)
        ; true)
    ; true).

% Helper predicate to delete a directory and its contents
delete_directory_and_contents(Dir) :-
    (exists_directory(Dir) ->
        directory_files(Dir, Files),
        maplist(delete_file_or_dir(Dir), Files),
        delete_directory(Dir)
    ; true).

delete_file_or_dir(Dir, File) :-
    (File \= '.' , File \= '..' ->
        atomic_list_concat([Dir, '/', File], FullPath),
        (exists_directory(FullPath) ->
            delete_directory_and_contents(FullPath)
        ;
            delete_file(FullPath)
        )
    ; true).

To run this Prolog program:

Save the code in a file named directories.pl.
Open SWI-Prolog console.
Load the file with [directories].
Run the main predicate with main.

The output will be similar to:

Listing subdir/parent
 child true
 file2 false
 file3 false
Listing subdir/parent/child
 file4 false
Visiting subdir
 subdir true
 subdir/file1 false
 subdir/parent true
 subdir/parent/child true
 subdir/parent/child/file4 false
 subdir/parent/file2 false
 subdir/parent/file3 false

This Prolog program demonstrates various directory operations:

Creating directories and files.
Listing directory contents.
Changing the current working directory.
Walking through a directory structure recursively.
Cleaning up temporary directories and files.

Note that Prolog doesn’t have built-in functions for all these operations, so we’ve used SWI-Prolog’s file system predicates and created helper predicates to mimic the functionality of the original Go program.

The main/0 predicate wraps all operations in a catch/3 to handle errors and ensure cleanup. The delete_directory_and_contents/1 predicate is used to remove the temporary directory and its contents at the end of the program.

Remember that Prolog is a logic programming language, so the approach to file system operations is quite different from imperative languages like Go. However, this example shows how similar functionality can be achieved in Prolog.

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Directories in Prolog