API for accessing hierarchical file systems. Clients use Paths to obtain Resources representing files or directories.

Path contains many useful operations for manipulating paths:

value path = parsePath("/Users/Trompon/Documents");
value child = path.childPath("hello.txt");
value sibling = child.siblingPath("goodbye.txt");
value parent = path.parent;

The attribute resource of Path is used to obtain a Resource. It is usually necessary to narrow a Resource to one of the following enumerated subtypes before performing operations on it:

• a File contains data,
• a Directory contains other resources,
• a Link is a symbolic link to another resource, or
• a Nil is an unoccupied location in the filesystem where a resource may safely be created.

To create a file named hello.txt in the home directory, we could do the following:

value filePath = home.childPath("hello.txt");
if (is Nil loc = filePath.resource) {
    value file = loc.createFile();
    try (writer = file.Overwriter()) {
        writer.writeLine("Hello, World!");
    }
}
else {
    print("file already exists");
}

Note the difference between a File.Overwriter, which destroys the existing contents of the file, if any, and a File.Appender, which leaves them intact.

To print the contents of the file we just created, we could do this:

value filePath = home.childPath("hello.txt");
if (is File file = filePath.resource) {
    try (reader = file.Reader()) {
        print(reader.readLine());
    }
}
else {
    print("file does not exist");
}

Now, to rename the file:

value filePath = home.childPath("hello.txt");
if (is File file = filePath.resource) {
    value newPath = filePath.siblingPath("goodbye.txt");
    if (is Nil loc = newPath.resource) {
       file.move(loc);
    }
    else {
        print("target file already exists");
    }
}
else {
    print("source file does not exist");
}

To list the contents of a directory, we have two possibilities. We can list just the direct contents:

if (is Directory dir = home.resource) {
    for (path in dir.childPaths()) {
        print(path);
    }
}
else {
    print("directory does not exist");
}

Alternatively, we can create a Visitor that walks the whole directory tree rooted at a given path:

object visitor extends Visitor() {
    file(File file) => print(file.path);
}
home.visit(visitor);

File systems other than the default file system are supported. For example, a file system for a zip file may be created using the convenience function createZipFileSystem().

value zipPath = home.childPath("myzip.zip");
if (is Nil|File loc = zipPath.resource) {
    value zipSystem = createZipFileSystem(loc);
    value entryPath = zipSystem.parsePath("/hello.txt");
    if (is Nil entry = entryPath.resource) {
        value filePath = home.childPath("hello.txt");
        if (is File file = filePath.resource) {
            file.copy(entry);
        }
        else {
            print("source file does not exist");
        }
    }
    else {
        print("entry already exists");
    }
    zipSystem.close();
}