std/io

Import with import std/io.

Exports

Modules

• IO

Types

• IOError

module IO

IOError

enum IOError {
    NotFound { path: String }
    Other { reason: String }
}

Distinguishable filesystem error variants returned by read_file and write_file. NotFound carries the path so callers can decide whether to treat absence as expected (e.g., first run of an app that creates its data file on demand). Other wraps any other failure with its raw error message.

print

fn print<'T>(value: 'T): Unit where 'T: Display

Prints a value’s user-facing representation to stdout, followed by a newline. The argument may be any value whose type implements Display — via an impl Display for T block or derive Display — and is stringified via Display.to_string. String implements Display as the identity, so IO.print("hello") prints hello unchanged; no need to pre-stringify other values. Use IO.inspect for the developer-facing Debug form.

IO.print("hello")   // prints: hello
IO.print(42)        // prints: 42

inspect

fn inspect<'T>(value: 'T): Unit

Prints a value’s runtime representation to stdout via Debug.inspect. Debug is universal — every value is inspectable with no derive/impl required (a structural impl is auto-synthesized for any type that doesn’t supply its own; opaque types render <opaque T>), so inspect carries no Debug bound. Write an explicit impl Debug implementation only to customize the rendering. Use dbg when you want to inspect a value while preserving it in an expression or pipeline.

IO.inspect([1, 2, 3])   // prints: [1, 2, 3]

read_line

fn read_line(): Result<String, String>

Reads a line from stdin. Returns Ok(line) with the newline stripped, or Err(“eof”) when stdin is closed.

case IO.read_line() {
  Ok(line) -> IO.print("got: " + line)
  Err(_) -> IO.print("done")
}

read_file

fn read_file(path: String): Result<String, IOError>

Reads the entire contents of path into a String.

IO.read_file("notes.txt")   // Ok("...") or Err(IO.IOError.NotFound{...})

write_file

fn write_file(path: String, content: String): Result<Unit, IOError>

Writes content to path, replacing any existing file. The parent directory must exist; missing parents do not get auto-created.

IO.write_file("notes.txt", "hello")