Standard streams and arguments

Output

write_stdout(text: str) -> Result[i64, IoError] and write_stderr(text) observe text and write its exact UTF-8 bytes without adding a newline. Success returns the Unicode-scalar count. Errors can follow partial output. Stderr writes go straight to descriptor 2, so a closed or read-only stderr is IoError.System(9) (EBADF). Stdout writes are buffered by the Rust standard library, which reports EBADF as success; a closed or read-only stdout discards output without an error.

print(values...) -> Result[(), IoError] formats supported values separated by spaces and adds a newline; no arguments produce an empty line; see formatting for allocation and Result restrictions. flush_stdout() and flush_stderr() return Result[(), IoError], exposing deferred buffered-write errors. These operations retain the process-owned stream handles. Success and flushing do not imply durable storage.

Input

input() -> Result[Option[str], IoError] reads one stdin line, removing LF or CRLF and preserving other characters. Some("") is an empty line; Nothing is EOF. Decoding is strict UTF-8.

Buffer growth and result construction are recoverable. Failure may consume a prefix or complete line; the reader does not read ahead into the next line. The current Unix backend reads the process descriptor directly. Prompt arguments, bare-CR newline translation and buffered stream objects are unsupported. Use input_bytes for binary records without newline conversion.

Arguments

args() -> Result[list[str], IoError] snapshots all executable arguments, including the invocation name at index zero. Each call produces an independent list with fallible text construction. Invalid UTF-8 is rejected rather than replaced or escaped; failed construction releases partial output. OS argument storage is only borrowed during construction. Use args_bytes for lossless Unix arguments and paths.