Open a file for a block

with open(path)? as file makes a stream available inside the indented block. It closes on exit, including on return, ?, break, or continue. The stream reference cannot escape the block.

open(path) opens an existing file for reading. open(path, "w") creates or truncates a file, and open(path, "a") creates or appends. Each returns Result[File, IoError]. Files move on assignment and cannot be copied.

read() returns text from the current position through EOF, translating CRLF and bare CR to LF and validating UTF-8. At EOF it returns an empty string.

Run this in a scratch directory: it replaces plenty-reading.txt.

def read_example() -> Result[str, IoError]:
    write_text("plenty-reading.txt", "hello\r\nworld")?
    with open("plenty-reading.txt")? as file:
        return Ok(file.read()?)

def main() -> Result[(), IoError]:
    print(read_example()?)?
    Ok(())

hello
world

The returned text owns its storage and survives closing the file. Read errors may consume input before failing. File I/O requires Linux.