Files

1 min read

Use File to read or write a whole file, inspect a path, or manage directories. Methods that wait for work are async and return Result values. Handle the error when the file cannot be accessed.

Import: import system.io;

Whole-file helpers are async and return Result. Call them from async fun main().

import system;
import system.io;

async fun main(): void {
    File.write("notes.txt", "hello\n").await;
    let text = (File.read("notes.txt").await).unwrap_or("");
    System.println(text);
}

Runtime	Where files live
Native / Node	Real disk
Browser	In-memory, gone on reload

Explore this topic

• Read and write streams
• Work with file paths

Whole file (File)

Call	Meaning
File.write.await / append	UTF-8 text
File.read.await / read_bytes / read_lines	whole file
File.write_bytes.await / write_lines	binary / lines
File.copy.await / rename	copy a file; same-volume move
File.delete.await	remove a file
File.remove_dir.await / remove_dir_all	empty dir / recursive
File.create_dir.await / create_dir_all	directories
File.list(path).await / list_paths	names, or joined paths
File.exists / size / is_dir / is_file / stat	sync probes
FileHandle.open / FileHandle.open_async.await	a FileHandle

File.stat returns FileStats (size, mtime_millis / ctime_millis / atime_millis, mode, kind) with is_file / is_dir / is_symlink. With import system;, modified() / created() yield DateTime.

Async File / FileHandle methods take an optional last token: Option<CancellationToken>; a cancelled token yields IoError with code ECANCELLED.